优雅地处理图像负载异常

Question

我正在使用Silverlight 3加载用户图像。一切正常，我可以将文件流设置为 BitmapImage 而且它变得还不错。

问题是，如果我尝试加载不是图像的东西（例如，已重命名为.png的.exe）Silverlight用A崩溃 System.Exception 那就是“灾难性的失败”。 MSDN文档无用地说应该这样做 MSDN链接 我应该听 ImageFailed 事件（永远不会被解雇）。

我在那里缺少某些东西，还是从流中加载时库会损坏？

我已经从源加载图像的代码：

        var openFileDialog = new OpenFileDialog();
        openFileDialog.Filter = "*.jpg;*.jpeg;*.png|*.jpg;*.jpeg;*.png";
        openFileDialog.Multiselect = false;
        var showDialog = openFileDialog.ShowDialog();

        if (showDialog.HasValue && showDialog.Value)
        {
            using (var reader = openFileDialog.File.OpenRead())
            {
                var picture = new BitmapImage();

                picture.DownloadProgress += (o, e) => System.Threading.SynchronizationContext.Current.Send((oo) => System.Windows.Browser.HtmlPage.Window.Alert("Download progress: " + e.Progress), null);
                picture.ImageFailed += (o, e) => System.Threading.SynchronizationContext.Current.Send((oo) => System.Windows.Browser.HtmlPage.Window.Alert("Image failed: " + e.ErrorException), null);
                picture.ImageOpened += (o, e) => System.Threading.SynchronizationContext.Current.Send((oo) => System.Windows.Browser.HtmlPage.Window.Alert("Image opened: " + e.OriginalSource), null);

                picture.SetSource(reader); // BANG! here without any of the alerts showing up
            }
        }

Answer 1

这很奇怪，但是您是对的，即使在Silverlight 4上，它也是如此。

可能有一个更好的选择，但是我发现解决这些异常的一种方法是修改application_unhandledexception（）方法。这对您有用：

private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
{
    // Handle stupid image load exception.  Can't think of a better way to do it -- sorry.
    if (e.ExceptionObject is System.Exception && e.ExceptionObject.Message.Contains("HRESULT") && e.ExceptionObject.Message.Contains("E_UNEXPECTED"))
    {
        Deployment.Current.Dispatcher.BeginInvoke(() =>
            {
                MessageBox.Show("Error loading image.");
            });
        e.Handled = true;
        return;
    }

    // If the app is running outside of the debugger then report the exception using
    // the browser's exception mechanism. On IE this will display it a yellow alert 
    // icon in the status bar and Firefox will display a script error.
    if (!System.Diagnostics.Debugger.IsAttached)
    {

        // NOTE: This will allow the application to continue running after an exception has been thrown
        // but not handled. 
        // For production applications this error handling should be replaced with something that will 
        // report the error to the website and stop the application.
        e.Handled = true;
        Deployment.Current.Dispatcher.BeginInvoke(delegate { ReportErrorToDOM(e); });
    }
}

这是一个黑客，我不喜欢它，但是比未经治疗的例外要好。

顺便说一句，您真的应该就此行为提交一个连接错误。当然，这使“最少惊讶的法律”失败了。请参阅Tim Heuer关于如何提交错误的帖子： http://timheuer.com/blog/archive/2010/05/03/ways-to-give-five-feedback-on-silverlight.aspx