Unhandled Exception

[blar58]

I have had little problem with managing threads lately.

Now I get this message which seems to come from the ContextMenu elements that I have added.

The message read like this :

Unhandled exception : Element already has a logical parent. It must be detached from the old parent before it is attached to a new one.

I read the message but can't figure out what it exactly means. Have you gone through this before ?

Thank you

[NinjaTrader_PatrickH]

Hello blar58,

Thank you for your post.

The message indicates the object is already attached to a parent object (such as a button to a grid) and it appears an attempt to assign the object to a new parent object is attempted but the object has not been detached from the prior.

There are several discussions on the web concerning this message but it is specific to the code used. In general the description above is about as basic as it can be made. A quick Google search provides several different use case examples: https://www.google.com/webhp?sourcei...d+to+a+new+one

If you would like us to take a look please attach the relevant NinjaScript object to your response.

[blar58]

OK I found where the problem is but don't know what is wrong.

I took the example you have given on this forum for adding items to the Context Menu.

Here is my code :

Variables declaration :

private System.Windows.Controls.Separator splitSeparator;
private System.Windows.Controls.MenuItem fullContextMenuItem;
private System.Windows.Controls.MenuItem splitContextMenuItem;
private bool doOnce = true;

On state == State.Configure :

splitSeparator = new Separator();
splitContextMenuItem = new System.Windows.Controls.MenuItem() {Header = "Split" };
splitContextMenuItem.Click += splitContextMenuItem_Click;
fullContextMenuItem = new System.Windows.Controls.MenuItem() {Header = "Full" };
fullContextMenuItem.Click += fullContextMenu_Click;

On State == State.Terminated :

if( ChartControl != null )
{		
   if( splitSeparator != null )
      ChartControl.ContextMenu.Items.Remove(splitSeparator);
					
   if( fullContextMenuItem != null )
     ChartControl.ContextMenu.Items.Remove(fullContextMenuItem);
					
   if( splitContextMenuItem != null )
     ChartControl.ContextMenu.Items.Remove(splitContextMenuItem);
}

Now the problem comes here on that final step From OnBarUpdate :

if(doOnce)
{
   if( ChartControl != null )
   {
      ChartControl.Dispatcher.BeginInvoke( new Action(() =>
   {
          ChartControl.ContextMenu.Items.Add(splitSeparator);
          ChartControl.ContextMenu.Items.Add(fullContextMenuItem);
          ChartControl.ContextMenu.Items.Add(splitContextMenuItem);
          doOnce = false;
   }));

  }
}

On the trace file it is said that the error message comes from that final step coming form the OnBarUpdate method.


Thanks

[NinjaTrader_Matthew]

On the trace file it is said that the error message comes from that final step coming form the OnBarUpdate method.


Thanks

Your "DoOnce" flag is being set to false within the async action to OnBarUpdate (through BeginInvoke(), which is causing the action to be called repeatedly.

1. Move the flag outside of the dispatcher action
2. Or you could simplify to only set your property on CurrentBar == 0,
3. Or just do this in State.Historical which is only called once throughout the lifetime of the script.

Solution 1 - Move the flag outside of the dispatcher action

if (doOnce)
{
	if ( ChartControl != null )
	{
		ChartControl.Dispatcher.BeginInvoke( new Action(() =>
		{
			ChartControl.ContextMenu.Items.Add(splitSeparator);
			ChartControl.ContextMenu.Items.Add(fullContextMenuItem);
			ChartControl.ContextMenu.Items.Add(splitContextMenuItem);

		}));
	}
	doOnce = false; // set outside of the dispatcher which action runs ascyrnconsly to OnBarUpdate
}

Solution 2 - Or you could simplify to only set your property on CurrentBar == 0,

if (CurrentBar == 0) // only apply action on first bar on chart
{
	if ( ChartControl != null )
	{
		ChartControl.Dispatcher.BeginInvoke( new Action(() =>
		{
			ChartControl.ContextMenu.Items.Add(splitSeparator);
			ChartControl.ContextMenu.Items.Add(fullContextMenuItem);
			ChartControl.ContextMenu.Items.Add(splitContextMenuItem);
		}));
	}
}

Solution 3 - Or...You can just do this in OnStateChange during State.Historical

else if (State == State.Historical) // only called once throughout indicator lifetime.
{
	if (ChartControl != null)
	{
		ChartControl.Dispatcher.BeginInvoke( new Action(() =>
		{
			ChartControl.ContextMenu.Items.Add(splitSeparator);
			ChartControl.ContextMenu.Items.Add(fullContextMenuItem);
			ChartControl.ContextMenu.Items.Add(splitContextMenuItem);
		}));
	}
}

[blar58]

Matthew you are great !

Makes lot of sense. Thank you very much. Much appreciated

Thanks!