对象引用未设置为object.Windows.forms控件的实例导致此操作
我有一个例外。
我像这样为InitializeComponent（）创建了一个try catch。
try { InitializeComponent(); Auto_Complete(); } catch(Exception ex) { System.Windows.Forms.MessageBox.Show(ex.Message); } 然后我得到一个exception，说“对象引用未设置为对象的实例。”。
我一直在寻找错误的原因。
然后我发现错误是由于我在xaml中添加了一个控件。
xmlns:wf="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms"
这是我添加到xaml中的自动完成function的windows.forms控件。
但是这个例外使得它变得困难。
我创建了一个autocomplete（）函数并连接了文本框：
void Auto_Complete() { txtAutoProductCode.AutoCompleteMode = AutoCompleteMode.SuggestAppend; txtAutoProductCode.AutoCompleteSource = AutoCompleteSource.CustomSource; AutoCompleteStringCollection coll = new AutoCompleteStringCollection(); SqlCeCommand com = new SqlCeCommand("SELECT ProductCode FROM Category_Master(CategoryName)", con); SqlCeDataReader dr; try { dr = com.ExecuteReader(); while (dr.Read()) { string aProduct = dr.GetString(0); coll.Add(aProduct); } } catch (Exception ex) { System.Windows.Forms.MessageBox.Show(ex.Message, System.Windows.Forms.Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error); } txtAutoProductCode.AutoCompleteCustomSource = coll; } public MainWindow() { try { InitializeComponent(); Auto_Complete(); } catch(Exception ex) { System.Windows.Forms.MessageBox.Show(ex.ToString()); } }
这是例外
System.Windows.Markup.XamlParseException was unhandled HResult=-2146233087 Message='Initialization of 'Billing.MainWindow' threw an exception.' Line number '6' and line position '9'. Source=PresentationFramework LineNumber=6 LinePosition=9 StackTrace: at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri) at System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri) at System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream) at System.Windows.Application.LoadBamlStreamWithSyncInfo(Stream stream, ParserContext pc) at System.Windows.Application.LoadComponent(Uri resourceLocator, Boolean bSkipJournaledProperties) at System.Windows.Application.DoStartup() at System.Windows.Application.b__1(Object unused) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.DispatcherOperation.InvokeImpl() at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) 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, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) 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.PushFrameImpl(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.Run() at System.Windows.Application.RunDispatcher(Object ignore) at System.Windows.Application.RunInternal(Window window) at System.Windows.Application.Run(Window window) at System.Windows.Application.Run() at Billing.App.Main() in c:\Users\kamalmohan\Documents\Visual Studio 2012\Projects\Billing\Billing\obj\Debug\App.g.cs:line 0 at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException: System.InvalidOperationException HResult=-2146233079 Message=Cannot have nested BeginInit calls on the same instance. Source=PresentationFramework StackTrace: at System.Windows.FrameworkElement.BeginInit() at MS.Internal.Xaml.Runtime.ClrObjectRuntime.InitializationGuard(XamlType xamlType, Object obj, Boolean begin) InnerException:
这可能有助于您解决问题所在
XAMLParseException是WPF中引发的常见exception。 不幸的是，这不是很有帮助。
为了帮助找出真正的错误，您可以在Visual Studio中更早地打开exception报告。 默认组合键是Ctrl + Alt + E.从那里，选中所有框。
现在，代码中抛出的exception将在调试器中突出显示。