private void OnVisibilityChanged(object sender, VisibilityChangedEventArgs e)
{
if (e.Visible)
{
_imageDecoder?.Start();
}
else if (!e.Visible)
{
_imageDecoder?.Stop(); // Prevent unnecessary work
}
}
private async Task <ImageSource> LoadImageByUri(Uri uriSource, CancellationTokenSource cancellationTokenSource)
{
var randStream = await this.CurrentLoader.LoadImageStream(uriSource, cancellationTokenSource);
if (randStream == null)
{
throw new Exception("stream is null");
}
ImageSource imageSource = null;
bool hasDecoder = false;
//debug模式不允许Decoders,直接采用默认方案
if (!DesignMode.DesignModeEnabled)
{
var decoders = this.CurrentLoader.GetAvailableDecoders();
if (decoders.Count > 0)
{
int maxHeaderSize = decoders.Max(x => x.HeaderSize);
if (maxHeaderSize > 0)
{
byte[] header = new byte[maxHeaderSize];
var readStream = randStream.AsStreamForRead();
readStream.Position = 0;
await readStream.ReadAsync(header, 0, maxHeaderSize);
readStream.Position = 0;
var decoder = decoders.FirstOrDefault(x => x.IsSupportedFileFormat(header));
if (decoder != null)
{
var source = await decoder.InitializeAsync(this.Dispatcher, randStream,
cancellationTokenSource);
imageSource = source.ImageSource;
this.PixelHeight = source.PixelHeight;
this.PixelWidth = source.PixelWidth;
if (!cancellationTokenSource.IsCancellationRequested)
{
_imageDecoder?.Dispose();
Interlocked.Exchange(ref _imageDecoder, decoder);
if (_isControlLoaded)
{
_imageDecoder.Start();
}
}
hasDecoder = true;
}
}
}
}
if (!hasDecoder)
{
var bitmapImage = new BitmapImage();
await bitmapImage.SetSourceAsync(randStream).AsTask(cancellationTokenSource.Token);
this.PixelHeight = bitmapImage.PixelHeight;
this.PixelWidth = bitmapImage.PixelWidth;
imageSource = bitmapImage;
}
return(imageSource);
}