How to remove children from with another thread?

Question

mycode :

        Canvas myCanvas = new Canvas();
>       Rectangle myRectangle = new Rectangle();

>                  Task.Factory.StartNew(() =>
>                  {
>                         while(true)
>                          {
>                             myCanvas.Children.Clear();
>                            //do something
>                            for(int i=1;i<=100;i++)
>                            {
>                               myCanvas.Children.Add(myRectangle[i]);
>                            }
                           }
>                  }).ContinueWith(t =>
>                  {
> 
>                  }, System.Threading.CancellationToken.None, TaskContinuationOptions.None,
>                  TaskScheduler.FromCurrentSynchronizationContext());

I still got error : "Specified Visual is already a child of another Visual or the root of a CompositionTarget." what i should do?

This has nothing to do with threading. You are trying to add a control to the canvas when the control is already added to another container. A visual control in WPF cannot have more than one parent. — Abion47, Feb 05 '17 at 22:08
This happens because of the _while(true)_ part in the second loop, when the visual is already in CanvasX. — Ron, Feb 05 '17 at 22:10

score 1 · Accepted Answer · answered Feb 05 '17 at 22:28

1

You might want to use Dispatcher.Invoke method.

while (true)
{
     Dispatcher.Invoke(new Action(() => { myCanvas.Children.Clear(); }));
     for (int i = 1; i <= 100; i++)
     {
         Dispatcher.Invoke(new Action(() => { myCanvas.Children.Add(myRectangle[i]); }));
     }
}

Note that Invoke blocks the calling thread.

answered Feb 05 '17 at 22:28

Ron

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It's work!! Thank you very much. excuse me can you explain to me what different invoke and begininvoke ? – Kittinun Pongsukjai Feb 05 '17 at 22:39
When you use Invoke, the calling thread waits for completion. This is not true for BeginInvoke. See [this link](http://stackoverflow.com/questions/229554/whats-the-difference-between-invoke-and-begininvoke) or google it for other explanations. – Ron Feb 05 '17 at 22:50

How to remove children from with another thread?

1 Answers1