I am attempting to learn Xamarin Forms and MVVM (using MVVM Light) and i'm struggling to get off the ground w/ list view data binding using XAML. I have the following models.

public class MainMenuModel : GalaSoft.MvvmLight.ObservableObject
{
    private ObservableCollection<Models.Menus.Objects.MainMenuGroup> _groups;

    #region Properties
    public ObservableCollection<Models.Menus.Objects.MainMenuGroup> Groups { get { return this._groups; } }
    #endregion

    #region Constructor
    public MainMenuModel()
    {
        this._groups = new ObservableCollection<Objects.MainMenuGroup>();
    }
    #endregion
}

public class MainMenuGroup : GalaSoft.MvvmLight.ObservableObject
    {
        private string _name;
        private ObservableCollection<MainMenuItem> _menuitems;

        #region Properties
        public string Name
        {
            get
            {
                return this._name;
            }
            set
            {
                this._name = value;
                if (this._name != value)
                {
                    base.RaisePropertyChanged("Name");
                }
            }
        }

        public ObservableCollection<MainMenuItem> MenuItems
        {
            get
            {
                return this._menuitems;
            }
        }
        #endregion

        #region Constructors
        public MainMenuGroup()
        {
            this._menuitems = new ObservableCollection<MainMenuItem>();
        }
        #endregion
    }

public class MainMenuItem :  GalaSoft.MvvmLight.ObservableObject
    {
        private string _name;
        private string _image;
        private string _description;

        #region Properties
        public string Name
        {
            get
            {
                return this._name;
            }
            set
            {
                this._name = value;
                base.RaisePropertyChanged("Name");
            }
        }

        public string Image
        {
            get
            {
                return this._image;
            }
            set
            {
                this._image = value;
                base.RaisePropertyChanged("Image");
            }
        }

        public string Description
        {
            get
            {
                return this._description;
            }
            set
            {
                this._description = value;
                base.RaisePropertyChanged("Description");
            }
        }
        #endregion
    }

And the following ViewModel

public class MainMenuViewModel : MainViewModel
    {
        private Models.Menus.MainMenuModel _mainmenumodel;

        #region Constructor
        public MainMenuViewModel(INavigationService NavigationService)
        {
            this._mainmenumodel = new Models.Menus.MainMenuModel();
        }

        #endregion

        #region Properties
        public Models.Menus.MainMenuModel MainMenu
        {
            get
            {
                return _mainmenumodel;
            }
        }
        #endregion
    }

I'm trying to bind to the MainMenu.Groups ObservableCollection and display the MainMenu.Groups.MenuItems ObservableCollection for each group. I set the BindingContext in the Code Behind to the MainMenuViewModel object and I have the following XAML.

  <ListView
        x:Name="lstMainMenu"
        ItemsSource="{Binding MainMenu.Groups}" 
        IsGroupingEnabled="true" GroupDisplayBinding="{Binding Name}" >
    <ListView.ItemTemplate>
      <DataTemplate>
        <ImageCell ImageSource="{Binding Image}" Text="{Binding Name}"/>
      </DataTemplate>
    </ListView.ItemTemplate>
  </ListView>

The groups show up in my ListView, however the MenuItems do not.

I really could use some help. I'm tired of googling...

I have a TabbedPage which contains two other pages as it's children:

ChatsTabbedPage.xaml:

<TabbedPage 
        xmlns="http://xamarin.com/schemas/2014/forms" 
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
        xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms" 
        prism:ViewModelLocator.AutowireViewModel="True" 
        xmlns:local="clr-namespace:One;assembly=One"
        xmlns:v="clr-namespace:One.Views;assembly=One"
        xmlns:i18n="clr-namespace:One;assembly=One"
        x:Class="One.Views.ChatsTabbedPage"
        Title="Chats"
        BarBackgroundColor="{StaticResource navBarBackgroundColor}" x:Name="TabPage" >
    <TabbedPage.Children>
            <v:ChatsPhonePage 
                Title="Chats"
                Icon="ic_chat.png"
                Appearing="Handle_Appearing"
                >
            </v:ChatsPhonePage>
            <v:KontaktePage Title="{i18n:Translate Text=kontakte}"
                Icon="ic_contacts.png">
            </v:KontaktePage>
    </TabbedPage.Children>
</TabbedPage>

The other two pages ChatsPhonePage and KontaktePage are a ContentPage. I will only show the code of one page because they have a lot code...

KontaktePage:

<ContentPage 
    xmlns="http://xamarin.com/schemas/2014/forms" 
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
    xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms" 
    xmlns:i18n="clr-namespace:One;assembly=One"
    xmlns:local="clr-namespace:One;assembly=One"
    xmlns:controls="clr-namespace:ImageCircle.Forms.Plugin.Abstractions;assembly=ImageCircle.Forms.Plugin.Abstractions"
    prism:ViewModelLocator.AutowireViewModel="True" 
    x:Class="One.Views.KontaktePage"
    Title="{i18n:Translate Text=kontakte}">
    <ContentPage.Resources>
        <ResourceDictionary>
            <local:OneImageConverter x:Key="OneImageConverter" />
        </ResourceDictionary>
    </ContentPage.Resources>
    <ContentPage.Content>
        <StackLayout>
            <Entry Placeholder="{i18n:Translate Text=kontakte_suchen}"
                Margin="10"
                HorizontalOptions="FillAndExpand"
                Text="{Binding Suchtext}"
                TextChanged="Handle_TextChanged"
                Style="{StaticResource entryStyle}">
            </Entry>
            <ListView CachingStrategy="RecycleElement"
                Margin="10"
                x:Name="listViewUsers"
                ItemsSource="{Binding Users}"
                IsRefreshing="{Binding IsRefreshing}"
                IsPullToRefreshEnabled="true"
                RefreshCommand="{Binding RefreshDataCommand}"
                HasUnevenRows="true"
                ItemSelected="Handle_ItemSelected">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <ViewCell>
                            <Grid ColumnSpacing="2" Padding="5">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="40"></ColumnDefinition>
                                    <ColumnDefinition Width="*"></ColumnDefinition>
                                </Grid.ColumnDefinitions>
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="*"></RowDefinition>
                                    <RowDefinition Height="Auto"></RowDefinition>
                                </Grid.RowDefinitions>
                                <controls:CircleImage
                                    Grid.Row="0"
                                    Grid.Column="0" 
                                    HorizontalOptions="Center"
                                    VerticalOptions="Center"
                                    Source="{Binding image, Converter={StaticResource OneImageConverter}, ConverterParameter=placeholder_image.png}">
                                </controls:CircleImage>
                                <Label 
                                    Grid.Row="0"
                                    Grid.Column="1"
                                    Text="{Binding name}"
                                    TextColor="{StaticResource listFontColor}"
                                    Style="{StaticResource labelStyle}">
                                </Label>
                                <Label
                                    Grid.Row="1"
                                    Grid.Column="1"
                                    Style="{StaticResource labelSmallStyle}"
                                    Text="{Binding status}"
                                    TextColor="{Binding statusColor}">
                                </Label>
                            </Grid>
                        </ViewCell>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

When I start my app, everthing is fine and I can see ChatsPhonePage:

However, if I click on "Kontakte", it should show KontaktePage. Instead, nothing happens. It doesn't even change the TextColor of "Kontakte" to white. It just looks exactly like in the screenshot above.

If I click on "Chats" (no matter if I clicked on "Kontakte" before or not), the page completely dissapears, leaving it blank white:

This is only an issue in UWP. It's working in iOS and Android. Any ideas?

Hi,

i have a requirement to display image in the gallery application.

in android, i could easily done using below piece of code

Intent intent = new Intent();
            intent.AddFlags (ActivityFlags.NewTask);
            intent.SetAction(Intent.ActionView);
            intent.SetDataAndType(Android.Net.Uri.Parse(imageURL), "image/*");
            Application.Context.StartActivity ( intent );

is there any similar way in ios ?

thanks in advance.

Hi,
I'm experiencing the following problem:

• Clean Xamarin.Forms Shared Project in Visual Studio using ReSharper (intellisense working)
• Adding Xamarin.Forms ContentPage XAML to the project from Visual Studio template => Intellisense not working (e.g. "cannot resolve symbol 'System'")

I already searched through google and numerous Xamarin forums. All solutions presented there were futile:

• setting the Build Action of the XAML file to "Embedded Resource" => it was already set.
• setting the Custom Tool of the XAML file form "Build" to "UpdateDesignTimeXaml" => it already was set.
• correcting the namespace of the x:Class in the XAML file => it already was correct.
• updating Xamarin.Forms and everything else => it is uptodate (Xamarin.Forms 2.3.2.127)
• cleaning ReSharper cache
• deleting and restarting obj, and bin dirs in solution
• deleting .suo file

The only thing that helped so for until the restart of Visual Studio was to change the Build Action of the XAML to something else and back to "Embedded Resource". But after a restart the intellisense again did not work.

For the moment I solved the Problem by deleting the XAML file again but that cannot be the solution. Can anyone help me with this problem? It is quiet a dealbreaker for Xamarin.Forms.

Best Regards!

Hello everyone,

I've been working on a project requiring Trusted Platform Modules on Windows 8 and Windows 10 (UWP) for a moment. I would like to use the Non-Volatile storage functionality of those chips in order to store some cryptographic keys.

I wasn't able to find any implementations of TPM on Xamarin so i am using an abstract class and platform specific code.

I use TSS.MSR library in order to perform actions with a TPM however my TPM is blocking some commands like NvDefineStorage or even Hash.

Exception raised by NvDefineStorage on UWP project

Tpm2Lib.TpmException: Error {None} was returned for command NvDefineSpace.
Details:
[Code=TpmRc.None],[RawCode=0x80280400,2150106112]
[ErrorEntity=Unknown], [ParmNum=0]
[ParmName=Unknown]
at Tpm2Lib.Tpm2.ProcessError(TpmSt responseTag, UInt32 responseParamSize, TpmRc resultCode, TpmStructureBase inParms)
at Tpm2Lib.Tpm2.DispatchMethod(TpmCc ordinal, TpmStructureBase inParms, Type expectedResponseType, TpmStructureBase& outParms, Int32 > numInHandlesNotUsed, Int32 numOutHandlesNotUsed)
at Tpm2Lib.Tpm2.NvDefineSpace(TpmHandle authHandle, Byte[] auth, NvPublic publicInfo)
at TestNvStorage.App.StoreData(Byte[] data)

It looks like some commands are blocked by Windows or GroupPolicies (https://technet.microsoft.com/en-us/library/cc771635(v=ws.11).aspx) so i specified in those policies to ignore the local blocked command list and also ignore the default blocked list (there is no command in the list of blocked commands).

I'm not able to access to command management in tpm.msc (if you have any idea why, it could help)

I also don't have TPM registry key in HKEY_LOCAL_MACHINE\SOFTWARE\Policies\WindowsTPM so it also can be a reason to my issues.

Now the TPM commands shouldn't be blocked anymore nevertheless i'm still not able to perform those commands.

There is my UWP code:

UWP application (Not Working with TPM)

using System;
using System.Diagnostics;
using System.Linq;
using Windows.ApplicationModel;
using Windows.ApplicationModel.Activation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;
using Tpm2Lib;

namespace TestNvStorage
{
sealed partial class App : Application
{
public static int indexTMPSlot = 3001;
public static AuthValue nvAuthValue = new AuthValue(new byte[] { 3, 4, 5, 6, 7, 8, 9 });

    public static void StoreData(byte[] data)
    {
        Tpm2Device tpmDevice;
        tpmDevice = new TbsDevice();
        tpmDevice.Connect();
        var tpm = new Tpm2(tpmDevice);

        var ownerAuth = new AuthValue();
        TpmHandle nvHandle = TpmHandle.NV(indexTMPSlot);
        tpm[ownerAuth]._AllowErrors().NvUndefineSpace(TpmHandle.RhOwner, nvHandle);

        AuthValue nvAuth = nvAuthValue;

        tpm[ownerAuth].NvDefineSpace(TpmHandle.RhOwner, nvAuth,
        new NvPublic(nvHandle, TpmAlgId.Sha1,
            NvAttr.Authwrite | NvAttr.Authread,
            new byte[0], 32));

        tpm[nvAuth].NvWrite(nvHandle, nvHandle, data, 0);
        tpm.Dispose();
        Debug.WriteLine(String.Format("Data Stored:\t{0}", Convert.ToBase64String(data)));
    }

    public static byte[] ReadData(int tailleData)
    {
        Tpm2Device tpmDevice;
        tpmDevice = new TbsDevice();
        tpmDevice.Connect();
        var tpm = new Tpm2(tpmDevice);

        TpmHandle nvHandle = TpmHandle.NV(indexTMPSlot);

        AuthValue nvAuth = nvAuthValue;

        byte[] newData = tpm[nvAuth].NvRead(nvHandle, nvHandle, (ushort)tailleData, 0);

        tpm.Dispose();
        Debug.WriteLine(String.Format("Data retreived:\t{0}", Convert.ToBase64String(newData)));
        return newData;
    }

    public static void ClearTpmNvSpace()
    {
        Tpm2Device tpmDevice;
        tpmDevice = new TbsDevice();
        tpmDevice.Connect();
        var tpm = new Tpm2(tpmDevice);

        TpmHandle nvHandle = TpmHandle.NV(indexTMPSlot);
        var ownerAuth = new AuthValue();
        tpm[ownerAuth]._AllowErrors().NvUndefineSpace(TpmHandle.RhOwner, nvHandle);
        tpm.Dispose();
        Debug.WriteLine("TPM cleaned");
    }

   public App()
    {
        this.InitializeComponent();

        byte[] nvData = new byte[] { 10, 1, 22, 33, 14, 55, 6, 37, 8, 200, 1, 2, 3, 4, 5, 6, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6, 2, 3, 4, 5, 6 };
        StoreData(nvData);
        byte[] newBytes = ReadData(nvData.Length);
        Debug.WriteLine(String.Format("Data Matching:\t{0}", nvData.SequenceEqual(newBytes)));
        ClearTpmNvSpace();
    }

}

}

I had some advices from Paul England to add Shared User Certificates in my UWP manifest capabilities so i followed the instructions. I also tried to run Visual studio to run my debug as Administrator but still not able to make it work on my UWP project.

Funny thing is i'm able to run my code (exactly the same) on a basic Windows console application flawlessly.

Windows Console application (Working with TPM)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Tpm2Lib;

namespace TestNvStorageConsole
{
class Program
{
public static int indexTMPSlot = 3001;
public static AuthValue nvAuthValue = new AuthValue(new byte[] { 3, 4, 5, 6 ,7,8,9});

    public static void StoreData(byte[] data)
    {
        Tpm2Device tpmDevice;
        tpmDevice = new TbsDevice();
        tpmDevice.Connect();
        var tpm = new Tpm2(tpmDevice);

        var ownerAuth = new AuthValue();
        TpmHandle nvHandle = TpmHandle.NV(indexTMPSlot);
        tpm[ownerAuth]._AllowErrors().NvUndefineSpace(TpmHandle.RhOwner, nvHandle);

        AuthValue nvAuth = nvAuthValue;

        tpm[ownerAuth].NvDefineSpace(TpmHandle.RhOwner, nvAuth,
        new NvPublic(nvHandle, TpmAlgId.Sha1,
            NvAttr.Authwrite | NvAttr.Authread,
            new byte[0], 32));

        tpm[nvAuth].NvWrite(nvHandle, nvHandle, data, 0);
        tpm.Dispose();
        Debug.WriteLine(String.Format("Data Stored:\t{0}", Convert.ToBase64String(data)));
    }

    public static byte[] ReadData(int tailleData)
    {
        Tpm2Device tpmDevice;
       tpmDevice = new TbsDevice();
        tpmDevice.Connect();
        var tpm = new Tpm2(tpmDevice);
        
        TpmHandle nvHandle = TpmHandle.NV(indexTMPSlot);

        AuthValue nvAuth = nvAuthValue;
        
        byte[] newData = tpm[nvAuth].NvRead(nvHandle, nvHandle, (ushort)tailleData, 0);

        tpm.Dispose();
        Debug.WriteLine(String.Format("Data retreived:\t{0}", Convert.ToBase64String(newData)));
        return newData;
    }

    public static void ClearTpmNvSpace()
    {
        Tpm2Device tpmDevice;
        tpmDevice = new TbsDevice();
        tpmDevice.Connect();
        var tpm = new Tpm2(tpmDevice);

        TpmHandle nvHandle = TpmHandle.NV(indexTMPSlot);
        var ownerAuth = new AuthValue();
        tpm[ownerAuth]._AllowErrors().NvUndefineSpace(TpmHandle.RhOwner, nvHandle);
        tpm.Dispose();
        Debug.WriteLine("TPM cleaned");
    }

    static void Main(string[] args)
    {
        byte[] nvData = new byte[] {10, 1, 22, 33, 14, 55, 6, 37, 8, 200, 1,2,3,4,5,6,2,3,4,5,1,2,3,4,5,6,2,3,4,5,6};
        StoreData(nvData);
        byte[] newBytes = ReadData(nvData.Length);
        Debug.WriteLine(String.Format("Data Matching:\t{0}",nvData.SequenceEqual(newBytes)));
        ClearTpmNvSpace();
    }
}

}

If anyone does have an idea to solve this issue or maybe another method to use TPM with Xamarin, I'm open to suggestions.

Tanguy

I'm trying to implement a listview that has a image in it where the image is bound to a thumbnail property as using the raw photos just kills performance of the listview. This thumbnail property resizes the main picture and then adds it to a thumbnail cache - therefore when the thumbnail property is called again for any photo - if it exists - it just grabs it from the cache. This works how I expect when the list loads up (and there are images already on the device) - however when I add an image to the list via the camera - the thumbnail property fires - it doesn't find it in the cache and goes through the resizing routine.. but the resizing routine for some reason creates an empty byte[] from the stream its passed in and therefore the thumbnail never shows.

What I've seen is that when the image is added to the list, the property fires off, but the resizing routine only fires when the image comes into view - that is fine, but what happens is that when the user attempts to look at the thumbnail of the photo straight after creating it, the thumbnail is not created - so to me it sounds like the image hasn't finished creating itself (before it attempts to resize it). If you wait a few seconds before scrolling to the new item in the list, the thumbnail appears everytime. I can't figure out where I'm going wrong!

This is my property that I'm binding to in my listview with the resizing routine:

private ImageSource thumbnailImage;

        public ImageSource thumbnail
        {
          get
          {
            if (thumbnailImage == null)
            {
                // Get photo from filesystem
                thumbnailImage = ImageSource.FromStream(() => getImage(Image.details).Result);
              }
            }

            return thumbnailImage;
          }
        }

        private async Task<Stream> getImage(string imgFileName)
        {
          if (!thumbnailCache.ContainsKey(Image))
          {
            var imgFile = await FileSystem.Current.LocalStorage.GetFileAsync(imgFileName);
            byte[] fileContents;
            using (Stream x = await imgFile.OpenAsync(FileAccess.Read))
            {
              fileContents = DependencyService.Get<IMediaService>().ResizeImage(x, 100, 100);
            }
            thumbnailCache.Add(Image, fileContents);
            return new MemoryStream(fileContents);
          }
          else
            return new MemoryStream(thumbnailCache[Image]);
        }

Hello, i'm new to Xamarin and i need some tips , i'm trying to figure it out how to start to develop XF for UWP.

The UI its very similar to a Masterdetailpage but i don't know if i can put buttons on the top and side bar. Can i do this with Grid?

What do you think is the best way forward?

I am using xamarin.forms light theme but I didnt like something about it. textcolor of the elements is white. it is a big conflict when theme is light and textcolor of label is white, you dont see the text. I want to extend it for some font and textcolor for each element. So how can I set for example all labels textcolor as black for entire app?

I have a problem with prism.forms and propertychanged.

I have settingsmodel,settingsviewmodel and settingspage that shown code below,

SettingsModel

public class SettingsModel: BindableBase
{
    public string Url { get; set; }
    public bool IsEnabled{get;set;}
    public string ApiUrl { get; set; }


    public SettingsModel()
    {
        this.Url = string.Empty;
        this.IsEnabled = false;
        this.ApiUrl = string.Empty;
    }
}

SettingsViewModel

[ImplementPropertyChanged]
public class SettingsPageViewModel : ViewModelBase
{

    readonly INavigationService _navigationService;
    readonly IUserDialogs _userDialogs;
    readonly IProductService _productService;

    #region Constructor

    public SettingsPageViewModel(INavigationService navigationService,
                              IUserDialogs userDialogs, IProductService productService)
    {
        _navigationService = navigationService;
        _userDialogs = userDialogs;
        _productService = productService;

        this.Settings = new SettingsModel();

        SaveCommand = new DelegateCommand(Save).ObservesCanExecute((vm) => Settings.IsEnabled);

    }

    #endregion


    #region Model


    SettingsModel _settingsModel;
    public SettingsModel Settings
    {
        get { return _settingsModel; }
        set { 

             if (_settingsModel != null)
                _settingsModel.PropertyChanged -= MyPersonOnPropertyChanged;

            SetProperty(ref _settingsModel, value); 


             if (_settingsModel != null)
                _settingsModel.PropertyChanged += MyPersonOnPropertyChanged;

            Validation();
        }
    }


    public bool IsLoading { get; set; }

    public DelegateCommand SaveCommand { get; set; }
    #endregion


    void MyPersonOnPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
    {
        Validation();
    }

    #region Methods

    async void Save()
    {

        var result = await _productService.GetProducts(Priority.UserInitiated,"","","");

    }

    void Validation()
    {
        Settings.IsEnabled = !string.IsNullOrEmpty(Settings.ApiUrl) ? true : false;
    }




    #endregion
}

And SettingsPage XAML

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" 
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
    xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms" 
    prism:ViewModelLocator.AutowireViewModel="True" 
    x:Class="XXX.Warehouse.SettingsPage">

<Entry Text="{Binding Settings.ApiUrl}" Margin="0,5,0,5"
       Placeholder="www.example.com" HorizontalOptions="FillAndExpand" />
<Button Text="Save"
        FontSize="16"
        BorderRadius="5"
        TextColor="White"
        BackgroundColor ="#578A17"
        IsEnabled="{Binding Settings.IsEnabled}"
        Command="{Binding SaveCommand}" />

I want to do when user enter url than IsEnabled property will true, when Url is empty than IsEnabled property will false and save button if IsEnabled is false, button not enabled.

My main problem is, i write Entry url but propertychanged event not fired?

How can i solve this?

Thank you.

Hello everyone, i found something strange in my application, in 1/30 (ios) and 1/1000 (android) i got strange exception in this 2 lines :

StackLayoutName.Children.Insert(StackLayoutName.Children.IndexOf(elementToRemove), temp);                               
    StackLayoutName.Children.Remove(elementToRemove);

I checked everything, no nulls in variables, no index out of range, no any mistake that i can't found, but i get exception.
Can anyone help me with it?

Сообщение: Object reference not set to an instance of an object
Тип: System.NullReferenceException
  at Xamarin.Forms.BindableObject.GetContext (Xamarin.Forms.BindableProperty property) [0x00013] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:489 
  at Xamarin.Forms.BindableObject.GetValue (Xamarin.Forms.BindableProperty property) [0x0000e] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\BindableObject.cs:54 
  at Xamarin.Forms.Layout.get_Padding () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:84 
  at Xamarin.Forms.Layout.GetSizeRequest (System.Double widthConstraint, System.Double heightConstraint) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:111 
  at Xamarin.Forms.VisualElement.Measure (System.Double widthConstraint, System.Double heightConstraint, Xamarin.Forms.MeasureFlags flags) [0x00054] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\VisualElement.cs:527 
  at Xamarin.Forms.StackLayout.CalculateNaiveLayout (Xamarin.Forms.StackLayout+LayoutInformation layout, Xamarin.Forms.StackOrientation orientation, System.Double x, System.Double y, System.Double widthConstraint, System.Double heightConstraint) [0x00236] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:185 
  at Xamarin.Forms.StackLayout.CalculateLayout (Xamarin.Forms.StackLayout+LayoutInformation layout, System.Double x, System.Double y, System.Double widthConstraint, System.Double heightConstraint, System.Boolean processExpanders) [0x00058] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:110 
  at Xamarin.Forms.StackLayout.OnSizeRequest (System.Double widthConstraint, System.Double heightConstraint) [0x00019] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:67 
  at Xamarin.Forms.VisualElement.OnMeasure (System.Double widthConstraint, System.Double heightConstraint) [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\VisualElement.cs:593 
  at Xamarin.Forms.VisualElement.GetSizeRequest (System.Double widthConstraint, System.Double heightConstraint) [0x00053] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\VisualElement.cs:469 
  at Xamarin.Forms.Layout.GetSizeRequest (System.Double widthConstraint, System.Double heightConstraint) [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:110 
  at Xamarin.Forms.VisualElement.Measure (System.Double widthConstraint, System.Double heightConstraint, Xamarin.Forms.MeasureFlags flags) [0x00054] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\VisualElement.cs:527 
  at Xamarin.Forms.StackLayout.CalculateNaiveLayout (Xamarin.Forms.StackLayout+LayoutInformation layout, Xamarin.Forms.StackOrientation orientation, System.Double x, System.Double y, System.Double widthConstraint, System.Double heightConstraint) [0x000a8] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:150 
  at Xamarin.Forms.StackLayout.CalculateLayout (Xamarin.Forms.StackLayout+LayoutInformation layout, System.Double x, System.Double y, System.Double widthConstraint, System.Double heightConstraint, System.Boolean processExpanders) [0x00058] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:110 
  at Xamarin.Forms.StackLayout.OnSizeRequest (System.Double widthConstraint, System.Double heightConstraint) [0x00019] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:67 
  at Xamarin.Forms.VisualElement.OnMeasure (System.Double widthConstraint, System.Double heightConstraint) [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\VisualElement.cs:593 
  at Xamarin.Forms.VisualElement.GetSizeRequest (System.Double widthConstraint, System.Double heightConstraint) [0x00053] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\VisualElement.cs:469 
  at Xamarin.Forms.Layout.GetSizeRequest (System.Double widthConstraint, System.Double heightConstraint) [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:110 
  at Xamarin.Forms.VisualElement.Measure (System.Double widthConstraint, System.Double heightConstraint, Xamarin.Forms.MeasureFlags flags) [0x00054] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\VisualElement.cs:527 
  at Xamarin.Forms.StackLayout.CalculateNaiveLayout (Xamarin.Forms.StackLayout+LayoutInformation layout, Xamarin.Forms.StackOrientation orientation, System.Double x, System.Double y, System.Double widthConstraint, System.Double heightConstraint) [0x000a8] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:150 
  at Xamarin.Forms.StackLayout.CalculateLayout (Xamarin.Forms.StackLayout+LayoutInformation layout, System.Double x, System.Double y, System.Double widthConstraint, System.Double heightConstraint, System.Boolean processExpanders) [0x00058] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:110 
  at Xamarin.Forms.StackLayout.LayoutChildren (System.Double x, System.Double y, System.Double width, System.Double height) [0x0005b] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\StackLayout.cs:44 
  at Xamarin.Forms.Layout.UpdateChildrenLayout () [0x000c7] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:229 
  at Xamarin.Forms.Layout.OnSizeAllocated (System.Double width, System.Double height) [0x0000f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:194 
  at Xamarin.Forms.VisualElement.SizeAllocated (System.Double width, System.Double height) [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\VisualElement.cs:629 
  at Xamarin.Forms.Layout.ForceLayout () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:104 
  at Xamarin.Forms.Layout.InvalidateLayout () [0x00016] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:174 
  at Xamarin.Forms.Layout.OnInternalAdded (Xamarin.Forms.View view) [0x0002d] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:404 
  at Xamarin.Forms.Layout.InternalChildrenOnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00089] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Layout.cs:392 
  at (wrapper delegate-invoke) <Module>:invoke_void_object_NotifyCollectionChangedEventArgs (object,System.Collections.Specialized.NotifyCollectionChangedEventArgs)
  at System.Collections.ObjectModel.ObservableCollection

1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedAction action, System.Object item, System.Int32 index) [0x00000] in /Users/builder/data/lanes/3818/ad1cd42d/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/referencesource/System/compmod/system/collections/objectmodel/observablecollection.cs:351 
  at System.Collections.ObjectModel.ObservableCollection

1[T].Insert (System.Int32 index, T item) [0x00038] in /Users/builder/data/lanes/3818/ad1cd42d/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/referencesource/mscorlib/system/collections/objectmodel/collection.cs:103 
  at Xamarin.Forms.ObservableWrapper

Hello ppl! I am working with XF and i wonder how can i run my project to an iOS 10 simulator!

Hi,

I am trying to implement localization as descibed here: https://developer.xamarin.com/guides/xamarin-forms/advanced/localization/ for my xamarin forms project (Anroid, iOS, WindowsPhone).

For Windows Phone I had to add a class like this:

`
using System;
using Xamarin.Forms;
using System.Threading;
using System.Globalization;

[assembly: Dependency(typeof(OM_App.WinPhone.Localize))]

namespace MY_App.WinPhone
{
public class Localize : MY_App.ILocalize
{
public void SetLocale(CultureInfo ci) { }
public System.Globalization.CultureInfo GetCurrentCultureInfo()
{
return System.Threading.Thread.CurrentThread.CurrentUICulture;
}
}
}
`

I get a error on this line:

return System.Threading.Thread.CurrentThread.CurrentUICulture;

Fehler CS0234 Der Typ- oder Namespacename "Thread" ist im Namespace "System.Threading" nicht vorhanden. (Möglicherweise fehlt ein Assemblyverweis.)

which is german and roughly translates to:

Error CS0234 The Type- or Namespace-Name "Thread" is not available in the Namespace "System.Threading" (Maybe an Assemblyverweis is missing)

What is wrong?
Thanks!

Hi there

My phone (Android) has its locale set to en-us, but time on my phone is displayed in 24 hour format (as configured on the phone). This is respected by every single app on my phone.

However, I noticed today that when displaying a TimePicker on my Xamarin Forms app, Xamarin displays a 12 hr time picker (probably according to the system locale).

That's the first problem. Next is to actually render the time on the UI. Here again, Xamarin fails with a ToString("t") - not surprisingly since this is just based on the UI CultureInfo. So I would need a device-specific time formatting method or the device configuration.

Showing a picker and displaying something as typical as time on a UI is a feature I would expect to just work out of the box. Is there anything in Xamarin Forms I overlooked? And if not, is this a known issue (that hopefully will be fixed soon)?

Thanks,
Philipp

I am trying to update Xamarin.Forms from version="2.1.0.6529" to "2.2.0.31"
After the nuget update I get a bunch of error from Xlabs in the Resource.Designer.cs

Here are my packages

<package id="Acr.DeviceInfo" version="3.0.0" targetFramework="monoandroid5" />
  <package id="ExifLib.PCL" version="1.0.1" targetFramework="monoandroid5" />
  <package id="FreshMvvm" version="0.0.5" targetFramework="monoandroid51" />
  <package id="Newtonsoft.Json" version="7.0.1" targetFramework="monoandroid5" />
  <package id="Xamarin.Android.Support.Animated.Vector.Drawable" version="23.3.0" targetFramework="monoandroid60" />
  <package id="Xamarin.Android.Support.Design" version="23.3.0" targetFramework="monoandroid60" />
  <package id="Xamarin.Android.Support.v4" version="23.3.0" targetFramework="monoandroid60" />
  <package id="Xamarin.Android.Support.v7.AppCompat" version="23.3.0" targetFramework="monoandroid60" />
  <package id="Xamarin.Android.Support.v7.CardView" version="23.3.0" targetFramework="monoandroid60" />
  <package id="Xamarin.Android.Support.v7.MediaRouter" version="23.3.0" targetFramework="monoandroid60" />
  <package id="Xamarin.Android.Support.v7.RecyclerView" version="23.3.0" targetFramework="monoandroid60" />
  <package id="Xamarin.Android.Support.Vector.Drawable" version="23.3.0" targetFramework="monoandroid60" />
  <package id="Xamarin.Forms" version="2.2.0.31" targetFramework="monoandroid60" />
  <package id="Xamarin.GooglePlayServices.Base" version="25.0.0.0" targetFramework="monoandroid5" />
  <package id="Xamarin.GooglePlayServices.Location" version="25.0.0.0" targetFramework="monoandroid5" />
  <package id="Xamarin.GooglePlayServices.Maps" version="25.0.0.0" targetFramework="monoandroid5" />
  <package id="XLabs.Core" version="2.0.5782" targetFramework="monoandroid60" />
  <package id="XLabs.Forms" version="2.0.5782" targetFramework="monoandroid60" />
  <package id="XLabs.IoC" version="2.0.5782" targetFramework="monoandroid60" />
  <package id="XLabs.Platform" version="2.0.5782" targetFramework="monoandroid60" />
  <package id="XLabs.Serialization" version="2.0.5782" targetFramework="monoandroid60" />
  <package id="XLabs.Serialization.JSON" version="2.0.5782" targetFramework="monoandroid60" />

My Compile and Target are Android 6.0. Any ideas?

1>Resources\Resource.Designer.cs(2016,124,2016,150): error CS0117: 'Resource.Attribute' does not contain a definition for 'mediaRouteSettingsDrawable'
1>Resources\Resource.Designer.cs(2178,118,2178,146): error CS0117: 'Resource.Color' does not contain a definition for 'design_textinput_error_color'
1>Resources\Resource.Designer.cs(2291,121,2291,144): error CS0117: 'Resource.Dimension' does not contain a definition for 'design_fab_content_size'
1>Resources\Resource.Designer.cs(2301,135,2301,172): error CS0117: 'Resource.Dimension' does not contain a definition for 'design_navigation_padding_top_default'
1>Resources\Resource.Designer.cs(2314,118,2314,138): error CS0117: 'Resource.Dimension' does not contain a definition for 'design_tab_min_width'
1>Resources\Resource.Designer.cs(2315,123,2315,148): error CS0117: 'Resource.Dimension' does not contain a definition for 'dialog_fixed_height_major'
1>Resources\Resource.Designer.cs(2316,123,2316,148): error CS0117: 'Resource.Dimension' does not contain a definition for 'dialog_fixed_height_minor'
1>Resources\Resource.Designer.cs(2317,122,2317,146): error CS0117: 'Resource.Dimension' does not contain a definition for 'dialog_fixed_width_major'
1>Resources\Resource.Designer.cs(2318,122,2318,146): error CS0117: 'Resource.Dimension' does not contain a definition for 'dialog_fixed_width_minor'
1>Resources\Resource.Designer.cs(2324,138,2324,178): error CS0117: 'Resource.Dimension' does not contain a definition for 'mr_media_route_controller_art_max_height'
1>Resources\Resource.Designer.cs(2414,111,2414,126): error CS0117: 'Resource.Drawable' does not contain a definition for 'ic_setting_dark'
1>Resources\Resource.Designer.cs(2415,112,2415,128): error CS0117: 'Resource.Drawable' does not contain a definition for 'ic_setting_light'
1>Resources\Resource.Designer.cs(2426,115,2426,134): error CS0117: 'Resource.Drawable' does not contain a definition for 'mr_ic_settings_dark'
1>Resources\Resource.Designer.cs(2427,116,2427,136): error CS0117: 'Resource.Drawable' does not contain a definition for 'mr_ic_settings_light'
1>Resources\Resource.Designer.cs(2447,87,2447,90): error CS0117: 'Resource.Id' does not contain a definition for 'art'
1>Resources\Resource.Designer.cs(2451,91,2451,98): error CS0117: 'Resource.Id' does not contain a definition for 'buttons'
1>Resources\Resource.Designer.cs(2468,105,2468,126): error CS0117: 'Resource.Id' does not contain a definition for 'default_control_frame'
1>Resources\Resource.Designer.cs(2470,94,2470,104): error CS0117: 'Resource.Id' does not contain a definition for 'disconnect'
1>Resources\Resource.Designer.cs(2496,109,2496,134): error CS0117: 'Resource.Id' does not contain a definition for 'media_route_control_frame'
1>Resources\Resource.Designer.cs(2497,100,2497,116): error CS0117: 'Resource.Id' does not contain a definition for 'media_route_list'
1>Resources\Resource.Designer.cs(2498,109,2498,134): error CS0117: 'Resource.Id' does not contain a definition for 'media_route_volume_layout'
1>Resources\Resource.Designer.cs(2499,109,2499,134): error CS0117: 'Resource.Id' does not contain a definition for 'media_route_volume_slider'
1>Resources\Resource.Designer.cs(2509,94,2509,104): error CS0117: 'Resource.Id' does not contain a definition for 'play_pause'

Hoping to get some insight on this. I am trying to utilize Xamarin's ListView Recycling Cache strategy. Here is my XAML

<ListView x:Name="gridList" CachingStrategy="RecycleElement">
      <ScrollView x:Name="listScroller">
        <ListView.ItemTemplate>
          <DataTemplate>
            <ViewCell>
              <StackLayout>
                <Image Source="{Binding Image}"/>
              </StackLayout>
            </ViewCell>
          </DataTemplate>
        </ListView.ItemTemplate>
      </ScrollView>
    </ListView>

In my "code behind" (I say code behind because thats the term typically used in .NET) for this xaml page, I initialize the ItemsSource to a datatemplate using a custom cell that I made as such:

gridList.ItemTemplate = new DataTemplate(typeof(Classes.CustomGridCell));
gridList.ItemsSource = cells;
Content = gridList;

Here is my CustomGridCell implementation:

   Xamarin.Forms.Image cellImage;
    public CustomGridCell()
    {
        cellImage = new Xamarin.Forms.Image();
        View = cellImage;
    }

    protected override void OnBindingContextChanged()
    {
        base.OnBindingContextChanged();
        var item = BindingContext as XamarinMobile.ViewModels.GridCellViewModel;

        if (item == null)
            return;

        cellImage.Source = Xamarin.Forms.ImageSource.FromUri(new System.Uri(item.Image));

    }

And when I receive data, I iterate through my list of objects and add cells as such:

var stories = gridViewModel.GridList;
            foreach (MobileObjects.GridListStory story in stories.StoryList)
            {
                cells.Add(new ViewModels.GridCellViewModel { Image = story.SquareImageURL });
            }

What seems to be happening is, the first iteration of my collection of stories.StoryList hits the cells.Add line. In turn, I see my CustomGridCell OnBindingContextChanged method being hit. The problem is, it hits the first time and then never gets hit again. After putting a breakpoint on my cells.Add... code, I can see that this never gets called again. As if there's some type of exception which is never fired. Checking the ouput, I do not see any kind of errors. But the foreach is essentially being thrown out after the first iteration and I don't even see that image.

When I change my CachingStrategy to RetainElement everything works fine and the iterations happen as they should. Hoping someone sees an immediate problem with what I am doing. I took most of this from Xamarin website itself, but it's possible I missed something.

I have upgraded my project from Visual Studio 2013 to Visual Studio 2015 and now I get this error.
_Severity Code Description Project File Line Suppression State
Error Exception while loading assemblies: System.IO.FileNotFoundException: Could not load assembly 'Xamarin.GooglePlayServices.Tasks, Version=1.0.0.0, Culture=neutral, PublicKeyToken='. Perhaps it doesn't exist in the Mono for Android profile?
File name: 'Xamarin.GooglePlayServices.Tasks.dll'
at Java.Interop.Tools.Cecil.DirectoryAssemblyResolver.Resolve(AssemblyNameReference reference, ReaderParameters parameters)
at Xamarin.Android.Tasks.ResolveAssemblies.AddAssemblyReferences(ICollection`1 assemblies, AssemblyDefinition assembly, Boolean topLevel)
at Xamarin.Android.Tasks.ResolveAssemblies.Execute() Test.Droid
_

I am not even using any Google Play features so don't understand why I am getting this error, any idea what I need to do to resolve this.

Thanks

Hello!

I am running into an issue (one that I could probably resolve a different way, but I wanted to make sure this is an issue) where when OnAppearing gets called is different for Android and iOS.

As an example, I have a root TabbedPage, and then I PushModalAsync a LoginPage (ContentPage) on top of it, and afterwards PopModalAsync. For iOS, the OnAppearing method for the TabbedPage seems to get called when the TabbedPage gets created, as well as when the LoginPage gets popped. This makes sense to some extent according to the documentation as the TabbedPage is probably "visible" initially that I can't actually see, then LoginPage is pushed immediately, then when popped, the TabbedPage is visible again. (Just FYI, the documentation for OnAppearing says "When overridden, allows application developers to customize behavior immediately prior to the Xamarin.Forms.Page becoming visible."

For Android though, the OnAppearing method gets called at the beginning, but not again when after the PopModalAsync. Has anyone else ran into this behavior? Anyone know at least a quick solution for now (as in a way to force call OnAppearing on the TabbedPage from the LoginPage)?

Thank you!

I have an Entry (and an Editor) throwing a Java.Lang.ArrayIndexOutOfBoundsException sometimes. It seems to be thrown when the user types and erases a lot.
The exception is uncatchable and, when it is thrown, the entire application crashes. Bummer.

More info (including code) here: http://stackoverflow.com/questions/40022969/xamarin-forms-entry-throwing-java-lang-arrayindexoutofboundsexception

Any help greatly appreciated. Been pulling my hair for a while already.

Iam getting image source from Camera plugin, then how can i convert image file path to base64 for saving in DB.
getting path like this /storage/emulated/0/Android/data/AvanteGardeCamera.Droid/files/Pictures/Sample/test_29.jpg.

I am trying to figure out how to have dynamic column widths in a grid that is inside a ListView. I have successfully got the row height of the ListView bound but (<ColumnDefinition Width="{Binding PictureWidth}" />) seems to have no affect. If i set it to a hard number (<ColumnDefinition Width="60" />) it works fine...?

<ListView   x:Name="listView" ItemsSource="{Binding ParentPage.Patients.Patients}" RowHeight="{Binding RowHeight}"  >
      <ListView.ItemTemplate>
        <DataTemplate>
          <ViewCell>
            <Grid HorizontalOptions="FillAndExpand">
              <Grid.RowDefinitions>
                <RowDefinition Height="*" />
              </Grid.RowDefinitions>
              <Grid.ColumnDefinitions>
                <ColumnDefinition Width="{Binding PictureWidth}" />
                <ColumnDefinition Width="*" />
              </Grid.ColumnDefinitions>
              <Image  Grid.Row="0" Grid.Column="0"
                 Source="{Binding Picture}"
                  />

              <Label BindingContext="{x:Reference PictureWidthSlider}" TextColor="Green" Text="{Binding Value}"
           HorizontalOptions="Center" />
              <Label BindingContext="{x:Reference RowHeightSlider}" TextColor="Red" Text="{Binding Value}"
           HorizontalOptions="Center" />

              <Label  Grid.Row="0" Grid.Column="1"
                      Text="{Binding FullName}"  />             
            </Grid>     
          </ViewCell>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>