How do I use Dispatcher.BeginInvoke properly?

Question

I have searched almost everywhere on the internet, and I have googled so many times and found so many results, but I still can't find the solution to my problem. I am busy converting an old `WinForms` application to a new WPF application but I am having trouble with some of the commands. In the Winforms application they use `Control.BeginInvoke()` and store this in an IAsyncResult object. I have read that the `Dispatcher.BeginInvoke()` is the `WPF` equivalent to the `Control.BeginInvoke()` for `WinForms` but I get this error when I use Dispatcher.BeginInvoke(): "Cannot implicitly convert type 'System.Windows.Threading.DispatcherOperation' to 'System.IAsyncResult'. An explicit conversion exists (are you missing a cast?)". Any help will be appreciated. Here is the code that I am trying to convert. This is the original `WinForms` code. I am able to convert everything except the BeginInvoke part. ``` private eSkan.api.TeSkanAPI feSkanAPI = null; private void MessageFilter_AddRemove_Invoke…

Accepted Answer

That's because `Dispatcher.BeginInvoke`, though it may be the equivalent logical operation, doesn't return an `IAsyncResult`, it returns a `DispatcherOperation`. Have a look at this blog post and you'll see a good example on how the `Dispatcher` works. I have copied the relevant code example into here to ensure it exists later.

```
public Window1()
{
  InitializeComponent();

CheckBox myCheckBox = new CheckBox();
  myCheckBox.Content = "A Checkbox";

System.Threading.Thread thread = new System.Threading.Thread(
    new System.Threading.ThreadStart(
      delegate()
      {
        System.Windows.Threading.DispatcherOperation
          dispatcherOp = myCheckBox.Dispatcher.BeginInvoke(
          System.Windows.Threading.DispatcherPriority.Normal,
          new Action(
            delegate()
            {
              myCheckBox.IsChecked = true;
            }
        ));

dispatcherOp.Completed += new EventHandler(dispatcherOp_Completed);
      }
  ));

thread.Start();
}

void dispatcherOp_Completed(object sender, EventArgs e)
{
  Console.WriteLine("The checkbox has finished being updated!");
}
```

Take note to this line:

```
dispatcherOp.Completed += new EventHandler(dispatcherOp_Completed);
```

that's how you're going to know when it's completed - it's going to call back to you via that event.

How do I use Dispatcher.BeginInvoke properly?

Solution

Problem