BackgroundWorker method executing twice

scody

Below is the skeleton code which demonstrates the way I have used the BackgroundWorker class. I followed the example provided in MSDN. For some reason MyTimeConsumingTask executes twice before the bgWorker_RunWorkerCompleted handles it. Any help would be greatly appriciated.

    //Form Class
    void bgWorker\_DoWork(object sender, DoWorkEventArgs e)
    {
        // Get the BackgroundWorker that raised this event.
        BackgroundWorker worker = sender as BackgroundWorker;

        e.Result = MyTimeConsumingTask(e.Argument, worker, e);

    }

    void bgWorker\_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        // First, handle the case where an exception was thrown.
        if (e.Error != null)
        {
            MessageBox.Show(e.Error.Message);
        }
        else if ((bool)e.Result)
        {
            //MyTimeConsumingTask successfully executed
        }
        else
        {
            //MyTimeConsumingTask failed
        }
    }
    //Form Class end


    //Another Class
    internal bool MyTimeConsumingTask(object arg, BackgroundWorker worker, DoWorkEventArgs e)
    {
        //Actual task is performed here, for simplicity sleep has been used.
        Thread.Sleep(10000);
        return true;
    }
    //Another Class end

N a v a n e e t h

Put break points and step into the code to see what is wrong.

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Steve Echols

You're not accidentally adding another handler to DoWork are you? bgWorker.DoWork += new DoWorkEventHandler(bgWorker_DoWork); bgWorker.DoWork += new DoWorkEventHandler(bgWorker_DoWork); If you do that, it will be called twice.

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scody

Checked with break points at every line of code involving this event. Although the e.result of first execution is true, the bgWorker_RunWorkerCompleted doesn't handle it but handles it after second execution. Below is the sequence of the code execution as traced by break points, strange but true...:confused:

BackgroundWorker worker = sender as BackgroundWorker; //bgWorker_DoWork handler
e.Result = MyTimeConsumingTask(e.Argument, worker, e); //bgWorker_DoWork handler

Thread.Sleep(10000); //MyTimeConsumingTask method
return true; //MyTimeConsumingTask mehtod

BackgroundWorker worker = sender as BackgroundWorker; //bgWorker_DoWork handler
e.Result = MyTimeConsumingTask(e.Argument, worker, e); //bgWorker_DoWork handler

Thread.Sleep(10000); //MyTimeConsumingTask method
return true; //MyTimeConsumingTask method

else if ((bool)e.Result) //bgWorker_RunWorkerCompleted handler

scody

Thanks Steve! You were right, I checked the whole project for DoWork and found that the Visual Studio had already added the DoWorkEventHandler in its generated code InitializeComponent() Now after removing it, works as expected. :-D

realJSOP

Try using trace statements instead of watching it through the debugger, and put a breakpoint at the end of the OnCompleted method. When the breakpoint is hit, examine the trace statements.

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