Stop theme started by backgroundworker
I have a window form that uses background work. The funnel launches an object and then executes a method on that object. My problem is that when I use backgroundworker.CancelAsync, the method that is started on the remote object does not stop. In the example below, the dowork method continues to execute after the cancel button is clicked. FYI, dowork loops through the spreadsheet and does some data manipulation based on the rows in the spreadsheet.
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
myObject newObject = new myObject();
newObject.dowork();
if (backgroundWorker1.CancellationPending)
{
e.Cancel = true;
backgroundWorker1.ReportProgress(0);
return;
}
}
private void btnCancel_Click(object sender, EventArgs e)
{
if (backgroundWorker1.IsBusy) backgroundWorker1.CancelAsync();
}
Thoughts?
thank
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As btnCancel_Click
you need to pass your request for cancellation of the work object; otherwise, he will never be notified. BackgroundWorker.CancelAsync()
does nothing, just sets the property BackgroundWorker.CancellationPending
, notifying the BackgroundWorker consumer (the UI, not the completed task) that your task has been canceled.
So what do you need:
MyObject myObject;
// This method is executed on the worker thread. Do not access your controls
// in the main thread from here directly.
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
myObject = new MyObject();
// The following line is a blocking operation in this thread.
// The user acts in the UI thread, not here, so you cannot do here
// anything but wait.
myObject.DoWork();
// Now DoWork is finished. Next line is needed only to notify
// the caller of the event whether a cancel has happened.
if (backgroundWorker1.CancellationPending)
e.Cancel = true;
myObject = null;
}
private void btnCancel_Click(object sender, EventArgs e)
{
if (backgroundWorker1.IsBusy)
{
backgroundWorker1.CancelAsync();
// You must notify your worker object as well.
// Note: Now you access the worker object from the main thread!
// Note2: It would be possible to pass the worker to your object
// and poll the backgroundWorker1.CancellationPending from there,
// but that would be a nasty pattern. BL objects should not
// aware of the UI components.
myObject.CancelWork();
}
}
And how should the notification be implemented:
public class MyObject
{
// normally you should use locks to access fields from different threads
// but if you just set a bool from one thread and read it from another,
// then it is enough to use a volatile field.
private volatile bool isCancelRequested;
// this will be called from the main thread
public void CancelWork()
{
isCancelRequested = true;
}
// This method is called from the worker thread.
public void DoWork()
{
// Make sure you poll the isCancelRequested field often enough to
// react to the cancellation as soon as possible.
while (!isCancelRequested && ...)
{
// ...
}
}
}
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