How to invoke on the UI thread of a WinForm Component?
I'm coding a WinForm component where I start a Task to do the actual processing and trap the exception on a continuation. From there I want to show the exception message on a UI element.
Task myTask = Task.Factory.StartNew (() => SomeMethod(someArgs));
myTask.ContinueWith (antecedant => uiTextBox.Text = antecedant.Exception.Message,
TaskContinuationOptions.OnlyOnFaulted);
Now I get a cross-thread exception because the task is trying to update a UI element from a, obviously, non UI thread.
H开发者_如何学Cowever, there is no Invoke or BeginInvoke defined in the Component class.
How to proceed from here?
UPDATE
Also, please note that Invoke/BeginInvoke/InvokeRequired are not available from my Component-derived class since Component doesn't provide them.
You could just add a property to your component, allows the client to set a form reference that you can use to call its BeginInvoke() method.
That can be done automatically as well, preferable so nobody can forget. It requires a bit of design time magic that's fairly impenetrable. I didn't come up with this by myself, I got it from the ErrorProvider component. Trusted source and all that. Paste this into your component source code:
using System.Windows.Forms;
using System.ComponentModel.Design;
...
[Browsable(false)]
public Form ParentForm { get; set; }
public override ISite Site {
set {
// Runs at design time, ensures designer initializes ParentForm
base.Site = value;
if (value != null) {
IDesignerHost service = value.GetService(typeof(IDesignerHost)) as IDesignerHost;
if (service != null) this.ParentForm = service.RootComponent as Form;
}
}
}
The designer automatically sets the ParentForm property when the user drops your component on a form. Use ParentForm.BeginInvoke().
You can use delegates to do this.
delegate void UpdateStatusDelegate (string value);
void UpdateStatus(string value)
{
if (InvokeRequired)
{
// We're not in the UI thread, so we need to call BeginInvoke
BeginInvoke(new UpdateStatusDelegate(UpdateStatus), new object[]{value});
return;
}
// Must be on the UI thread if we've got this far
statusIndicator.Text = value;
}
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