如何使用MVVM和Xamarin在XAML中动态更改图像源

Question

I'm trying to change an image source property on a ContentPage . I´m using a binding context to do this. But, even if I change the source in my model view, this don't update the image in my view.

UpdateMethod()
{
    imageSource1 = imageSource[1];
}

public string ImageSource1
{
    get
    {
        return imageSource1;
    }

    set
    {
        imageSource1 = value;
        this.Notify("ImageSource1");
    }
}

The XAML:

<ContentView HorizontalOptions="Center" Grid.Row="0" >
    <Image ClassId = "1" Source="{Binding ImageSource1}" BindingContextChanged="Handle_BindingContextChanged">
        <Image.GestureRecognizers>
            <TapGestureRecognizer  Command="{Binding OnTapGestureRecognizerTappedCommand1}" NumberOfTapsRequired="1" />
        </Image.GestureRecognizers>
    </Image>            
</ContentView>

Answer 1

Image component accepts ImageSource ( FileImageSource , StreamImageSource etc). Luckily ImageSource class have implicit operator against string which creates itself from string regarding format(url or path). Check below Example:

Xaml

<Image Source="{Binding ImagePath}">
  <Image.GestureRecognizers>
    <TapGestureRecognizer Command="{Binding ImageTapCommand}" />
  </Image.GestureRecognizers>
</Image>

ViewModel.cs:

public class SomeViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public ICommand ImageTapCommand { get; set; }


    private string imagePath;
    public string ImagePath
    {
        get { return imagePath; }
        set
        {
            imagePath = value;
            PropertyChanged(this, new PropertyChangedEventArgs("ImagePath"));
        }
    }

    public SomeViewModel()
    {
        ImageTapCommand = new Command(CmdTapImage);
    }


    private void CmdTapImage()
    {
        ImagePath = YourNewImagePath;
    }
}

Answer 2

When you are Binding the ImageSource use the Xamarin.Forms.ImageSource as the return type of your property. Or you can use it's derived classes like FileImageSource if you are specifying a filepath. Also make sure that the path is present in the native projects.

Answer 3

First add de ImageSource in your view model, don´t forget to include Xamarin.Forms dependencys...

    private ImageSource _imageSource;
public ImageSource ImageSource
{
    get { return _imageSource; }
    set
    {
        _imageSource= value;
        PropertyChanged(this, new PropertyChangedEventArgs("ImageSource"));
    }
}

after this, include de source binding in you xaml file:

     <Image Source="{Binding ImageSource}">
        <!--<Image.GestureRecognizers>
            <TapGestureRecognizer Command="{Binding ImageTapCommand}" />
        </Image.GestureRecognizers>-->
    </Image>

Here is a "prism example"

        private ImageSource _imageSource;
    public ImageSource ImageSource
    {
        get { return _imageSource; }
        set { SetProperty(ref _imageSource, value); }
    }