假设我正在使用后台工作器,并且我有以下方法:
private void bw_DoWork(object sender, DoWorkEventArgs e)
{
finalData = MyWork(sender as BackgroundWorker, e);
}
private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
int i = e.ProgressPercentage; // Missused for i
Debug.Print("BW Progress Changed Begin, i: " + i + ", ThreadId: " + Thread.CurrentThread.ManagedThreadId);
// I use this to update a table and an XY-Plot, so that the user can see the progess.
UpdateGUI(e.UserState as MyData);
Debug.Print("BW Progress Changed End, i: " + i + ", ThreadId: " + Thread.CurrentThread.ManagedThreadId);
}
private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if ((e.Cancelled == true))
{
// Cancelled
}
else if (!(e.Error == null))
{
MessageBox.Show(e.Error.Message);
}
else
{
Debug.Print("BW Run Worker Completed Begin, ThreadId: " + Thread.CurrentThread.ManagedThreadId);
// I use this to update a table and an XY-Plot,
// so that the user can see the final data.
UpdateGUI(finalData);
Debug.Print("BW Run Worker Completed End, ThreadId: " + Thread.CurrentThread.ManagedThreadId);
}
}
现在我假设在调用bw_RunWorkerCompleted
方法之前,bw_ProgressChanged
方法已经完成了。但事实并非如此,我不明白为什么。
我收到以下输出:
Worker, i: 0, ThreadId: 27
BW Progress Changed Begin, i: 0, ThreadId: 8
BW Progress Changed End, i: 0, ThreadId: 8
Worker, i: 1, ThreadId: 27
BW Progress Changed Begin, i: 1, ThreadId: 8
BW Progress Changed End, i: 1, ThreadId: 8
Worker, i: 2, ThreadId: 27
BW Progress Changed Begin, i: 2, ThreadId: 8
BW Run Worker Completed Begin, ThreadId: 8
BW Run Worker Completed End, ThreadId: 8
A first chance exception of type 'System.InvalidOperationException' occurred in mscorlib.dll
ERROR <-- Collection was modified; enumeration operation may not execute.
ERROR <-- NationalInstruments.UI.WindowsForms.Graph.ClearData()
MagagedID 8是
主线程
,27是一个工作线程
。我可以在Debug / Windows / Threads中看到这一点。如果我在方法中不调用
UpdateGUI
,则不会发生任何错误。但是用户无法在表格和XY图中看到任何进度。
编辑
MyWork
方法看起来像这样:public MyData[] MyWork(BackgroundWorker worker, DoWorkEventArgs e)
{
MyData[] d = new MyData[n];
for (int i = 0; i < n; i++)
d[i] = null;
for (int i = 0; i < n; i++)
{
if (worker.CancellationPending == true)
{
e.Cancel = true;
break;
}
else
{
d[i] = MyCollectDataPoint(); // takes about 1 to 10 seconds
Debug.Print("Worker, i: " + i + ", ThreadId: " + Thread.CurrentThread.ManagedThreadId)
worker.ReportProgress(i, d);
}
}
return d;
}
UpdateGUI
方法如下:
private void UpdateGUI(MyData d)
{
UpdateTable(d); // updates a DataGridView
UpdateGraph(d); // updates a ScatterGraph (NI Measurement Studio 2015)
}
如果我不调用
UpdateGraph
方法,则结果符合预期。因此ProgressChanged
方法已在执行RunWorkerCompleted
之前完成。所以我猜问题出在NI Measurement Studio 2015的
ScatterGraph
和BackgroundWorker
的组合上。但我不明白为什么会这样?
UpdateGraph
方法如下:private void UpdateGraph(MyData d)
{
plot.ClearData();
plot.Plots.Clear(); // The error happens here (Collection was modified; enumeration operation may not execute).
int n = MyGetNFromData(d);
for (int i = 0; i < n; i++)
{
ScatterPlot s = new ScatterPlot();
double[] xi = MyGetXiFromData(d, i);
double[] yi = MyGetYiFromData(d, i);
s.XAxis = plot.XAxes[0];
s.YAxis = plot.YAxes[0];
s.LineWidth = 2;
s.LineColor = Colors[i % Colors.Length];
s.ProcessSpecialValues = true;
s.PlotXY(xi, yi);
plot.Plots.Add(s);
}
}
编辑2
如果我在bw_RunWorkerCompleted
方法中设置一个断点,那么调用堆栈看起来像这样:
bw_RunWorkerCompleted
[External Code]
UpdateGraph // Line: plot.ClearData()
UpdateGUI
bw_ProgressChanged
[External Code]
Program.Main
并且第一个[外部代码]
块:
System.dll!System.ComponentModel.BackgroundWorker.OnRunWorkerCompleted(System.ComponentModel.RunWorkerCompletedEventArgs e) Unknown
[Native to Managed Transition]
mscorlib.dll!System.Delegate.DynamicInvokeImpl(object[] args) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbackDo(System.Windows.Forms.Control.ThreadMethodEntry tme) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(object obj) Unknown
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx) Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx) Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallback(System.Windows.Forms.Control.ThreadMethodEntry tme) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbacks() Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.MarshaledInvoke(System.Windows.Forms.Control caller, System.Delegate method, object[] args, bool synchronous) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.Invoke(System.Delegate method, object[] args) Unknown
System.Windows.Forms.dll!System.Windows.Forms.WindowsFormsSynchronizationContext.Send(System.Threading.SendOrPostCallback d, object state) Unknown
NationalInstruments.Common.dll!NationalInstruments.Restricted.CallbackManager.CallbackDispatcher.SynchronousCallbackDispatcher.InvokeWithContext(System.Delegate handler, object sender, System.EventArgs e, System.Threading.SynchronizationContext context, object state) Unknown
NationalInstruments.Common.dll!NationalInstruments.Restricted.CallbackManager.a(NationalInstruments.Restricted.CallbackManager.CallbackDispatcher A_0, object A_1, object A_2, System.EventArgs A_3) Unknown
NationalInstruments.Common.dll!NationalInstruments.Restricted.CallbackManager.RaiseEvent(object eventKey, object sender, System.EventArgs e) Unknown
NationalInstruments.Common.dll!NationalInstruments.ComponentBase.RaiseEvent(object eventKey, System.EventArgs e) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.XYCursor.OnAfterMove(NationalInstruments.UI.AfterMoveXYCursorEventArgs e) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.XYCursor.a(object A_0, NationalInstruments.Restricted.ControlElementCursorMoveEventArgs A_1) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYCursorElement.OnAfterMove(NationalInstruments.Restricted.ControlElementCursorMoveEventArgs e) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYCursorElement.a(NationalInstruments.UI.Internal.CartesianPlotElement A_0, double A_1, double A_2, int A_3, bool A_4) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYCursorElement.MoveCursorFreely(double xValue, double yValue, bool isInteractive, NationalInstruments.UI.Internal.XYCursorElement.Movement movement) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYCursorElement.MoveCursorXY(double xValue, double yValue, bool isInteractive) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYCursorElement.ResetCursor() Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYCursorElement.a(object A_0, NationalInstruments.Restricted.ControlElementEventArgs A_1) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.PlotElement.OnDataChanged(NationalInstruments.Restricted.ControlElementEventArgs e) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.PlotElement.OnDataChanged() Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.CartesianPlotElement.a(object A_0, NationalInstruments.UI.Internal.PlotDataChangedEventArgs A_1) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYDataManager.a(NationalInstruments.UI.Internal.PlotDataChangedEventArgs A_0) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYDataManager.a(NationalInstruments.UI.Internal.PlotDataChangeCause A_0, int A_1) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.XYDataManager.ClearData(bool raiseDataChanged) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.CartesianPlotElement.ClearData(bool raiseDataChanged) Unknown
NationalInstruments.UI.dll!NationalInstruments.UI.Internal.PlotElement.ClearData() Unknown
NationalInstruments.UI.dll!NationalInstruments.Restricted.XYGraphManager.ClearData() Unknown
NationalInstruments.UI.WindowsForms.dll!NationalInstruments.UI.WindowsForms.Graph.ClearData() Unknown
UpdateGUI
是否调用任何异步方法,其中您不等待任务完成? - René Vogti
的哪个值是最后一个进度更改事件)? - René Vogtif (i < n - 1) worker.ReportProgress(i, d);
可以避免错误,但这是一种非常愚蠢的解决方法。我不喜欢那样做。我想要理解它。 - WollmichApplication.ThreadException
处理程序全局捕获异常),而且它并不能真正解释后来的枚举异常。 - René Vogt