wpf - 强制 WPF BitmapImage 从其 UriSource 重新加载

Question

我正在尝试构建一个基于 Image 的自定义控件，它只是使图像在计时器上重新加载(从相同的 URI)。原始图像显示正常，但似乎没有刷新。

这里是自定义控件:

public class RefreshImage : Image
{
    protected override void OnInitialized(EventArgs e)
    {
        base.OnInitialized(e);
        this.Loaded += RefreshImage_Loaded;
    }

    private void RefreshImage_Loaded(object sender, RoutedEventArgs e)
    {
        var timer = new DispatcherTimer();
        timer.Interval = TimeSpan.FromSeconds(1);
        timer.Tick += RefreshImage_Tick;
        timer.Start();
    }

    private void RefreshImage_Tick(object sender, System.EventArgs e)
    {
        var bm = (BitmapImage) Source;
        bm.InvalidateProperty(BitmapImage.UriSourceProperty);
    }
 }

我是这样使用它的:

  <custom:RefreshImage>
      <Image.Source>
          <BitmapImage UriCachePolicy="NoCacheNoStore"
                       CreateOptions="IgnoreImageCache" CacheOption="None"
                       UriSource="{Binding Uri}"/>
      </Image.Source>
  </custom:RefreshImage>

InvalidateProperty 的文档似乎表明这正是我所需要的:

You can also use InvalidateProperty to force re-evaluation of a binding against a data source that is not able to implement the recommended INotifyPropertyChanged notification mechanism.

在 Uri 上引发 INotifiyPropertyChanged.PropertyChanged 事件也不会触发图像重新加载。

Answer 1

一般来说，BitmapSource 似乎是不可变对象(immutable对象)。一旦它们完成初始化，任何进一步的属性更改都将被忽略。我怀疑这包括 UriSource。

以下阶段在 MSDN post on creating custom ImageSources 中经常重复:

The ISupportInitialize interface is used to snap the values of theproperties when initialization is complete. Further changes to theproperties are ignored.