如何捕获此 WPF 位图加载异常？

Question

我正在开发一个使用 .NET 3.5 sp1 和 C# 从网络加载位图的应用程序。

加载代码如下所示：

        try {
            CurrentImage = pics[unChosenPics[index]];
            bi = new BitmapImage(CurrentImage.URI);
            // BitmapImage.UriSource must be in a BeginInit/EndInit block.
            bi.DownloadCompleted += new EventHandler(bi_DownloadCompleted);
            AssessmentImage.Source = bi;
        }
        catch {
            System.Console.WriteLine("Something broke during the read!");
        }

在 bi_DownloadCompleted 上加载的代码为：

    void bi_DownloadCompleted(object sender, EventArgs e) {
        try {
            double dpi = 96;
            int width = bi.PixelWidth;
            int height = bi.PixelHeight;

            int stride = width * 4; // 4 bytes per pixel
            byte[] pixelData = new byte[stride * height];
            bi.CopyPixels(pixelData, stride, 0);

            BitmapSource bmpSource = BitmapSource.Create(width, height, dpi, dpi, PixelFormats.Bgra32, null, pixelData, stride);

            AssessmentImage.Source = bmpSource;
            Loading.Visibility = Visibility.Hidden;
            AssessmentImage.Visibility = Visibility.Visible;
        }
        catch {
            System.Console.WriteLine("Exception when viewing bitmap.");
        }
    }

每隔一段时间，就会出现一个让读者崩溃的图像。我想这是可以预料的。然而，异常显然不是被这些 try/catch 块中的任何一个捕获，而是被抛出到我可以处理的范围之外。我可以使用全局 WPF 异常来处理它，例如 这个问题。然而，这会严重扰乱我的程序的控制流程，如果可能的话我想避免这种情况。

我必须执行双源分配，因为似乎许多图像在 Microsoft 位图加载器期望的位置缺少宽度/高度参数。因此，第一个分配似乎强制下载，第二个分配使 dpi/图像尺寸正确发生。

我该怎么做才能捕获并处理这个异常？

如果您想复制，请尝试将此图像加载为 uri：

http://i.pbase.com/o2/26/519326/1/123513540.Yub8hciV.Longford12.jpg

异常本身是：

System.ArgumentException in PresentationCore
Value does not fall within the expected range.

内部异常是：

An invalid character was found in text context.

堆栈跟踪：

   at MS.Internal.HRESULT.Check(Int32 hr)
   at System.Windows.Media.Imaging.BitmapFrameDecode.get_ColorContexts()
   at System.Windows.Media.Imaging.BitmapImage.FinalizeCreation()
   at System.Windows.Media.Imaging.BitmapImage.OnDownloadCompleted(Object sender, EventArgs e)
   at System.Windows.Media.UniqueEventHelper.InvokeEvents(Object sender, EventArgs args)
   at System.Windows.Media.Imaging.LateBoundBitmapDecoder.DownloadCallback(Object arg)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Boolean isSingleParameter)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.TranslateAndDispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Application.RunInternal(Window window)
   at LensComparison.App.Main() in C:\Users\Mark64\Documents\Visual Studio 2008\Projects\LensComparison\LensComparison\obj\Release\App.g.cs:line 48
   at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

Answer 1

此异常是图像中包含的颜色配置文件信息“损坏”的结果。如果您不关心此信息（或者想在异常后再次尝试解析），请使用 BitmapCreateOptions.IgnoreColorProfile 标志。

示例：

BitmapImage i = new BitmapImage();
i.BeginInit();
i.CreateOptions |= BitmapCreateOptions.IgnoreColorProfile;
i.UriSource = new Uri(@"http://www.bing.com/fd/hpk2/KiteFestival_EN-US2111991920.jpg");
i.EndInit();

如果您需要了解更多信息，请查看 Scott Hanselman 的帖子。 （今天我们都通过电子邮件就这个问题进行了沟通。）

Answer 2

这似乎有效：

try
{
    frame = BitmapFrame.Create(new Uri("http://i.pbase.com/o2/26/519326/1/123513540.Yub8hciV.Longford12.jpg"));
}
catch
{
    return;
}

BitmapFrame 有一个 DecodeFailed 事件，但我无法挂钩它，因为 BitmapFrame 在创建后被冻结。