我该如何捕获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：

        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上加载的代码如下：

    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.");
        }
    }

有时会出现一些图片会导致读者崩溃。我猜这是可以预料的。但是，异常似乎没有被try/catch块捕获，而是在我无法处理的地方抛出。我可以像这个SO问题中说的那样使用全局的WPF异常来处理它。但是，这将严重干扰程序的控制流，如果可能的话，我想避免这种情况。

我必须进行双重源分配，因为许多图像似乎缺少微软位图加载器需要的宽度/高度参数。所以，第一个分配似乎强制下载，第二个分配则使dpi/图像尺寸正确发生。

我应该怎么做来捕获和处理这个异常呢？

如果您想要复制，尝试将此图像作为URI加载：

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.

内部异常为：

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()

- mmr

---

顶一下...我在使用类似于海报的技术从Flickr加载任意图像时遇到了相同的问题。 - Josh Santangelo

Answer 1

这个异常是由于图像中包含了“损坏”的颜色配置文件信息导致的。如果您不关心此信息（或者想在异常后尝试重新解析），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();

如果你正在寻找更多信息，请查看Scott Hanselman的帖子。（今天我们通过电子邮件就此问题进行了沟通。）

- Rafael Rivera

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，但是我无法挂钩它，因为BitmapFrame在创建后被冻结了。

- Josh Santangelo