Accessing Array from OnRender causes "thread cannot access this object" error

[seykool]

Hi guys,

can you tell me why it throws the error "Error on calling 'OnRender' method on bar 2999: The calling thread cannot access this object because a different thread owns it."?

I have an Array of Brushes which gets accessed in a method that is called by OnRender. And whenever it does it, it throws the above error. When I access the array directly in OnRender, it still throws the error. When I access the array in OnBarUpdate, however, it doesn't throw the error and accesses the array's brush accordingly. My guess is that OnRender uses a different thread, but why it only happens with brush arrays, and how to solve it, I have little clue. Please advise me.

Greetings

[NinjaTrader_Jim]

Hello seykool,

Thanks for your post.

OnBarUpdate is generally on an instrument thread. OnRender will reside on a UI thread.

Are these brushes in your array custom brushes? If so, are you freezing them?

Are you properly disposing SharpDX brushes as well?

Please see the sections "Understanding Custom Brushes" and "Using advanced brush types" for more details:

https://ninjatrader.com/support/helpGuides/nt8/working_with_brushes.htm

If the matter is still unresolved, could you implement just enough code in a separate script and attach it here so I can better see what you are doing?

[seykool]

Hello Jim,
normally I do this. Nevertheless, I oversaw to freeze the Brushes of the array, this time. That has indeed been it. Thank you!

[seykool]

If I instantiate and initialize a SharpDX.Direct2D1.SolidColorBrush in a method and only use it there, do I have to dispose it thereafter?

[NinjaTrader_Jim]

Hello seykool,

If you are calling your own drawing methods in OnRender, and you have brushes created within the scope of those custom methods, those brushes should be disposed at the end of that method. (Similarly, if you have DX brushes created in OnRender's scope, they should be disposed at the end of OnRender.)

Alternatively, you can dispose and recreate resources in OnRenderTargetChanged, and keep those brushes as private properties. This is better on performance and you would not have to dispose those resources elsewhere, unless you needed to update them.

public override void OnRenderTargetChanged()
{
  // if dxBrush exists on first render target change, dispose of it
  if (dxBrush != null)
  {
    dxBrush.Dispose();
  }

  // recalculate dxBrush from value calculated in OnBarUpdated when RenderTarget is recreated
  if (RenderTarget != null)
    dxBrush = brushColor.ToDxBrush(RenderTarget);
}

OnRenderTargetChanged() - https://ninjatrader.com/support/help...getchanged.htm