使用INotifyPropertyChanged从BitmapImage变量绑定Image.Source

Question

I want to bind my CurrentWallpaper variable to Image.Source and update the Image control when it changes. That's my code:

public sealed partial class MainPage : Page, INotifyPropertyChanged
{
    public BitmapImage CurrWall = new BitmapImage();
    BitmapImage CurrentWallpaper
    {
        get { return CurrWall; }
        set { CurrWall = value; OnPropertyChanged("CurrentWallpaper"); }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

At the Page tag I've added this DataContext attribute.

DataContext="{Binding RelativeSource={RelativeSource Self}}"

And that is my Image control

<Image x:Name="CurrentWallpaperImage" Source="{x:Bind CurrWall}"/>

When i try to set a new source, the Image control doesn't update.

StorageFile file = await ApplicationData.Current.LocalFolder.GetFileAsync(path);
IRandomAccessStream stream = await file.OpenAsync(FileAccessMode.Read);
await CurrentWallpaper.SetSourceAsync(stream);

Answer 1

You are not actually assigning a new value to the CurrentWallpaper property of your page. So the OnPropertyChanged isn't triggered.

2 options, or you still use the SetSource method but after that line call the OnPropertyChanged("CurrentWallpaper"); yourself to ensure the UI is updated.

Or create a new BitmapImage with the stream you have and fully assing that new bitmapimage to your CurrentWallpaper.

CurrentWallpaper = newBitmapImage;

Answer 2

At first, declare CurrentWallpaper as public property

private BitmapImage currentWall = new BitmapImage();
public BitmapImage CurrentWallpaper
{
    get { return currentWall; }
    set { currentWall= value; OnPropertyChanged("CurrentWallpaper"); }
}

At second, change Binding to OneWay

<Image x:Name="CurrentWallpaperImage" Source="{x:Bind CurrWall, Mode=OneWay}"/>

If it will not work after first or second steps, try to raise event manually

await CurrentWallpaper.SetSourceAsync(stream);
OnPropertyChanged("CurrentWallpaper");