help. i did reuse BackgroundWorker. but the worker occured very strange behavior

Question

help.

i did reuse BackgroundWorker. but the worker occured very strange behavior.

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    //(!)note bw created at class scope, not button1_click.
    BackgroundWorker bw = new BackgroundWorker();

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        bw.DoWork+=new DoWorkEventHandler(bw_DoWork);
        bw.RunWorkerCompleted+=new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
        bw.RunWorkerAsync();
        System.Console.Beep(2000, 200);
    }

    void bw_DoWork(object sender, DoWorkEventArgs e)
    {
        System.Console.Beep(1000, 200);
    }

    void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        System.Console.Beep(2500, 200);
    }

}

it occured very strange behavior.

i expected beep sequence is beep(200,200)-beep(1000,200)-beep(2500,200).

yes. it did. but it's first time only.

*beep(200,200)=A
*beep(1000,200)=B
*beep(2500,200)=C

[when i click then button1 in second time]
A-B-B-C-C

[when i click then button1 in third time]
A-B-B-B-C-C-C

[when i click then button1 in fourth time]
A-B-B-B-B-C-C-C-C

???

what does this?

(*of cause, when i BackgroundWorker bw = new BackgroundWorker(); move to first line of button1_click, it works rightly)

Answer 1

Each time you click the button, you're adding another handler to the DoWork and RunWorkerCompleted events - so those delegates are both getting called one more time when you call RunWorkerAsync.

Personally I'd advise you to create one background worker on each click - but if you must reuse it, just attach the event handlers once (e.g. in the constructor).