我有应用程序应该将其数据库备份并恢复到 SkyDrive。但是,如果我在使用“开始”按钮(快速应用程序切换)向 SkyDrive 上传或下载备份时关闭应用程序,然后使用“返回”按钮返回应用程序,我会捕获未处理的 NullReferenceException:
void RestoreFromSkyDrive() {
ShowProgress();
LiveConnectClient client = new LiveConnectClient(App.Session);
string id = string.Empty;
if (client != null) {
client.GetCompleted += (obj, args) => {
try {
List<object> items;
if (args != null && args.Result != null && args.Result["data"] != null)
items = args.Result["data"] as List<object>;
else
return;
foreach (object item in items) {
Dictionary<string, object> file = item as Dictionary<string, object>;
// fileName is a name of backup-file
if (file != null && file["name"] != null && file["name"].ToString() == fileName) {
id = file["id"].ToString();
if (client != null) client.DownloadCompleted += new EventHandler<LiveDownloadCompletedEventArgs>(client_DownloadCompleted);
if (client != null) client.DownloadAsync(String.Format("{0}/content", id));
break;
}
}
}
catch (Exception ex) {
MessageBox.Show(ex.Message + " restore");
}
};
if (client != null) {
client.GetAsync("me/skydrive/files");
}
}
}
void client_DownloadCompleted(object sender, LiveDownloadCompletedEventArgs e) {
try {
if (e.Error == null) {
Stream stream = e.Result;
using (IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication()) {
var fileToSave = new IsolatedStorageFileStream(Constants.dbName, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None, storage);
stream.CopyTo(fileToSave);
stream.Flush();
stream.Close();
fileToSave.Close();
}
}
else {
MessageBox.Show(e.Error.Message + " dcompleted mb");
}
}
catch (WebException ex) { MessageBox.Show(ex.Message + " dcompleted ex"); }
HideProgress();
}
我插入了很多对 null 的检查,但无论如何我捕获了 NullReferenceException。我不知道我能用它做什么。
PS:启用 CLR 异常的 StackTrace:
System.Net.WebException occurred
Message=WebException
StackTrace:
at System.Net.Browser.ClientHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult)
at System.Net.Browser.ClientHttpWebRequest.<>c__DisplayClass2.<EndGetResponse>b__1(Object sendState)
at System.Net.Browser.AsyncHelper.<>c__DisplayClass4.<BeginOnUI>b__0(Object sendState)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(RuntimeMethodInfo rtmi, Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture, Boolean isBinderDefault, Assembly caller, Boolean verifyAccess, StackCrawlMark& stackMark)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, StackCrawlMark& stackMark)
at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
at System.Delegate.DynamicInvokeOne(Object[] args)
at System.MulticastDelegate.DynamicInvokeImpl(Object[] args)
at System.Delegate.DynamicInvoke(Object[] args)
at System.Windows.Threading.Dispatcher.<>c__DisplayClass4.<FastInvoke>b__3()
at System.Reflection.RuntimeMethodInfo.InternalInvoke(RuntimeMethodInfo rtmi, Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture, Boolean isBinderDefault, Assembly caller, Boolean verifyAccess, StackCrawlMark& stackMark)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, StackCrawlMark& stackMark)
at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
at System.Delegate.DynamicInvokeOne(Object[] args)
at System.MulticastDelegate.DynamicInvokeImpl(Object[] args)
at System.Delegate.DynamicInvoke(Object[] args)
at System.Windows.Threading.DispatcherOperation.Invoke()
at System.Windows.Threading.Dispatcher.Dispatch(DispatcherPriority priority)
at System.Windows.Threading.Dispatcher.OnInvoke(Object context)
at System.Windows.Hosting.CallbackCookie.Invoke(Object[] args)
at System.Windows.Hosting.DelegateWrapper.InternalInvoke(Object[] args)
at System.Windows.RuntimeHost.ManagedHost.InvokeDelegate(IntPtr pHandle, Int32 nParamCount, ScriptParam[] pParams, ScriptParam& pResult)
禁用 CLR 异常的 StackTrace:
System.NullReferenceException was unhandled
Message=NullReferenceException
StackTrace:
at Microsoft.Live.Operations.DownloadOperation.CompleteOperation(Exception error)
at Microsoft.Live.Operations.DownloadOperation.OnCancel()
at Microsoft.Live.Operations.WebOperation.OnGetWebResponse(IAsyncResult ar)
at System.Net.Browser.ClientHttpWebRequest.<>c__DisplayClassa.<InvokeGetResponseCallback>b__8(Object state2)
at System.Threading.ThreadPool.WorkItem.WaitCallback_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadPool.WorkItem.doWork(Object o)
at System.Threading.Timer.ring()