async task - System.InvalidOperationException - Invalid cross-thread operation-CodePudding

everyone,

I have a problem with handling an async task.

I have a timer and separately in a async Task, I wanted to run a state machine. Depending on what time is current, I wanted to run a status and write it to a label to display on the windows form.

I got the error System.InvalidOperationException - Invalid cross-thread operation.

private async void btnStart_Click(object sender, EventArgs e)
{         
    labelTimer.Text = mytimer.ToString(@"hh\:mm\:ss");
    // Timer Start
    timer1.Start();

    // Start StateMachine
    try
    {
        await stateMachine();
    }
    catch (Exception ex) 
    {
        MessageBox.Show(ex.ToString());
    }
    
}

private async Task stateMachine()
{
    await Task.Run(() =>
    {
        while (sMachine)
        {
            switch(labelTimer.Text)
            {
                case "00:00:55":
                    labelConsole.Text = "Works";
                    break;
            }
        }
    });
}

Does anyone have an idea how I can write to the Windows form from an async task?

CodePudding user response：

When you use Task.Run, you're pushing work to a non-UI thread; a non-UI thread cannot talk to to the UI - you need to get back to the UI for that; so instead of labelConsole.Text = "Works";, you'd need to do something like

Invoke((MethodInvoker)delegate{
    labelConsole.Text = "Works";
});

Note, however, that you'd also probably want a pause of some kind - you don't want to loop aggressively millions of times a second.