c# - Windows Phone 8.1 创建 WriteableBiitmap 时出现异常

Question

我正在制作一个 Windows Phone 8.1 应用程序(Windows 运行时，而不是 Silverlight 8.1)，我需要从流创建一个 WriteableBitmap，但是当我尝试这样做时，我得到了这个异常:“类型异常'System.Exception' 发生在 mscorlib.ni.dll 中，但未在用户代码中处理

Additional information: The component cannot be found. (Exception from HRESULT: 0x88982F50)"

我已经尝试了很多东西，但仍然没有运气。我的代码如下:

private async void Button_Click(object sender, RoutedEventArgs e)
{
    var files = await KnownFolders.CameraRoll.GetFilesAsync();
    for(int i=0; i<files.Count; i++)
    {
        var fileStream = await files[i].OpenReadAsync();
        if(fileStream != null)
        {
             WriteableBitmap writeableBmp = await BitmapFactory.New(1, 1).FromStream(fileStream);
        }
    }
}

但是如果我替换了就不会发生这种情况

var fileStream = await files[i].OpenReadAsync();

例如，

var fileStream = await files[0].OpenReadAsync();

有什么想法吗？谢谢。

Answer 1

这很奇怪。我认为您已经检查了 appxmanifest 文件中的“图片库”功能。

这段代码对我有用:

public static async Task<WriteableBitmap> GetWritableBitmapFromStream(Stream stream)
{
    var decoder = await BitmapDecoder.CreateAsync(stream.AsRandomAccessStream());
    var pixelData = await decoder.GetPixelDataAsync(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Ignore, new BitmapTransform(), ExifOrientationMode.IgnoreExifOrientation, ColorManagementMode.DoNotColorManage);
    var pixels = pixelData.DetachPixelData();

    var bmp = new WriteableBitmap((int)decoder.PixelWidth, (int)decoder.PixelHeight);
    using (var bmpStream = bmp.PixelBuffer.AsStream())
    {
        bmpStream.Seek(0, SeekOrigin.Begin);
        await bmpStream.WriteAsync(pixels, 0, (int)bmpStream.Length);
    }
    return bmp;
}

private async void Button_Click(object sender, RoutedEventArgs e)
{
    var files = await KnownFolders.CameraRoll.GetFilesAsync();
    foreach (var file in files)
    {
        // need "using System.IO" for this extension method
        using (var fileStream = await file.OpenStreamForReadAsync())
        {
            WriteableBitmap writeableBmp = await GetWritableBitmapFromStream(fileStream);
            // do something with writableBmp
        }
    }
}