WPF Enable / Disable DragMove delegate

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Hi all!

I got custom window which need to be dragged around but some cases I need to ignore dragging.

At the moment I subcribe delegate in window constructor

MouseLeftButtonDown += delegate { DragMove(); };

Which works fine and enables me to drag my custom window around

When I like to disable drag event I call

MouseLeftButtonDown -= delegate { DragMove(); };

Which does not work, Im still able to drag my custom window..

So how I properly unsubcribe my delegate?

Hope you got idea :)

Cheers!

Posted 20-Oct-11 1:35am

paleGegg0

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Wayne Gaylard · Accepted Answer · 2011-10-20T02:00:00

You should do this by creating a bool varaiable (call it canDrag) as a form level variable and explicitly creating a MouseLeftButtonDown event which will only drag if canDrag = true. Something like this:-

C#

bool canDrag = false;

       public MainWindow()
       {
           InitializeComponent();
           MouseLeftButtonDown +=new System.Windows.Input.MouseButtonEventHandler(MainWindow_MouseLeftButtonDown);
       }

       void MainWindow_MouseLeftButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
       {
           if (canDrag)
           {
               this.DragMove();
           }
       }

You can then set canDrag to true and false in the appropriate places. I used buttons to test like this:-

C#

private void btnDrag_Click(object sender, RoutedEventArgs e)
        {
            canDrag = true;
        }

        private void btnNoDrag_Click(object sender, RoutedEventArgs e)
        {
            canDrag = false ;
        }

Hope this helps

Simon Bang Terkildsen · Accepted Answer · 2011-10-20T02:30:00

Solution 2

The reason it doesn't work is because

C#

delegate { DragMove(); }

and

C#

delegate { DragMove(); }

and not equal thus the delegate is not removed.
You have to store the delegate in order to be able to remove it again, like this:

C#

MouseButtonEventHandler handler = delegate { GetMoreData(); };
MouseLeftButtonDown += handler;
MouseLeftButtonDown -= handler;

Posted 20-Oct-11 2:30am

Simon Bang Terkildsen

Comments

paleGegg0 21-Oct-11 0:25am

Hi! Thanks for your time! Did not knew that delegates work this way, now I know :)