No work await Task.Run():
private async void button2_Click(object sender, EventArgs e)
{
await Task.Run(() => {
monitor_r(label1);
});
}
protected async Task monitor_r(Label L1)
{
MessageBox.Show(L1.Name);
L1.ForeColor = Color.Blue;
L1.Text = "test";
}
These commands
MessageBox.Show(L1.Name);
and
L1.ForeColor = Color.Blue;
works fine but
L1.Text = "test";
does not work.
Can you help, why do not change a Label Text?
Try Control.Invoke: we should run Winform UI in the main thread only
protected async Task monitor_r(Label L1)
{
Action action = () =>
{
MessageBox.Show(L1.Name);
L1.ForeColor = Color.Blue;
L1.Text = "test";
};
if (L1.InvokeRequired)
L1.Invoke(action); // When in different thread
else
action(); // When in the main thread
}
If you're on debug mode, take a look at the output window. It should shows exception message something like this:
System.InvalidOperationException' in System.Windows.Forms.dll.
That because label1 accessed from a thread other than the thread it was created on. And it will causing invalid cross-thread operation.
You can solve this by using Control.Invoke as Dmitry Bychenko already mentioned. Here is simple extension to make thread-safe calls to Winforms Control.
public static void TryInvoke(this Control control, Action<Control> action)
{
if (control.InvokeRequired) control.Invoke(new Action(() => action(control)));
else action(control);
}
Sample usage
label1.TryInvoke(x => x.Text = "test");
label1.TryInvoke(x => x.ForeColor = Color.Blue);
Or
this.TryInvoke(x =>
{
label1.Text = "test";
label1.ForeColor = Color.Blue;
});
Secondly, since you don't await anything at monitor_r, i'd recommend to use void instead of async Task.
Even if you're await something at monitor_r you don't need
await Task.Run(() => {
monitor_r(label1);
});
..because monitor_r itself is a task. So just call await monitor_r(label1);
If you wish to have a separate thread, you can try this using BackgroundWorker. You can implement the ReportProgress if you have a loop.
private void button1_Click(object sender, EventArgs e)
{
BackgroundWorker worker = new BackgroundWorker()
{
WorkerReportsProgress = true,
WorkerSupportsCancellation = true
};
worker.RunWorkerCompleted += Worker_RunWorkerCompleted;
worker.RunWorkerAsync();
}
private void Worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
MessageBox.Show(label1.Name);
label1.ForeColor = Color.Blue;
label1.Text = "test";
}
