BUG: Exception raised when dynamically changing plot color (brush)

[strategesis]

According to the current documentation, the way to dynamically change the color (brush) of a plot is to assign a Brush into the appropriately-indexed sub-element of the PlotBrushes array: http://ninjatrader.com/support/helpG...lotbrushes.htm

Specifically, to dynamically change the color (brush) of the current bar for an indicator's first (zeroeth) plot to blue, one is supposed to evaluate the following statement:

PlotBrushes[0][0] = Brushes.Blue;

However, doing so raises the following exception:

The calling thread cannot access this object because a different thread owns it.
at System.Windows.Threading.DispatcherObject.VerifyAc cess()
at System.Windows.Freezable.Freeze(Boolean isChecking)
at NinjaTrader.NinjaScript.BrushSeries.Set(Int32 index, Brush value)
at NinjaTrader.NinjaScript.BrushSeries.set_Item(Int32 barsAgo, Brush value)
at NinjaTrader.NinjaScript.Indicators.N1MovAvgOmniMA. colorizePlot(Int32 plotIndex, Double nextValue)
at NinjaTrader.NinjaScript.Indicators.N1LightweightIn dicator.updatePlotAt(Int32 plotIndex)

Here's the relevant activation frames in my code, showing the path of execution from OnBarUpdate():

protected virtual void colorizePlot(int plotIndex, double nextValue) {
if (double.IsNaN(nextValue)) return;
var prevValue = prevPlotValue(plotIndex);
if (double.IsNaN(prevValue)) return;
switch (Math.Sign(nextValue - prevValue)) {
case 1:
PlotBrushes[plotIndex][0] = RisingBrush;
break;
default:
PlotBrushes[plotIndex][0] = NeutralDirectionBrush;
break;
case -1:
PlotBrushes[plotIndex][0] = FallingBrush;
break;
}
}

protected virtual void updatePlotAt(int plotIndex) {
var nextValue = computePlotValue(plotIndex);

try {
if (double.IsNaN(nextValue)) {
Values[plotIndex].Reset();
} else {
setPlotValue(plotIndex, nextValue);
if (colorizePlots) colorizePlot(plotIndex, nextValue);
}
} catch (Exception ex) {
logMessage(ex.Message);
logMessage(ex.StackTrace);
}
}

protected override void updatePlots() {
if (BarsInProgress != 0) return;
for (int plotIndex = 0; plotIndex < Values.Length; plotIndex++) {
updatePlotAt(plotIndex);
}
}

protected override void OnBarUpdate() {
preUpdatePlots();
updatePlots();
postUpdatePlots();
}

[NinjaTrader_Matthew]

Where are you declaring the RisingBrush, etc resources? And are they pre-defined brushes, or are you creating a new custom brush object?

I could not compile your example, but you likely have declared a new custom brush resource without freezing it before you tried to use it.

Please have a look on this topic under Creating a Solid Color Brush

http://ninjatrader.com/support/helpGuides/nt8/en-us/brushes.htm

For example, if you're doing something like I have written below, you'd get threading errors without first freezing the brush object as I have done in State.Configure

public class MyCustomIndicator : Indicator
	{
		SolidColorBrush myBrush;
		protected override void OnStateChange()
		{
			if (State == State.SetDefaults)
			{
				Description					= @"Enter the description for your new custom Indicator here.";
				Name						= "MyCustomIndicator";			
				AddPlot(Brushes.Green, "myPlot");
			}
			else if (State == State.Configure)
			{
				myBrush = new SolidColorBrush(Colors.Blue);
				// without freezing the brush, trying to use it later in OBU results in threading errors
				myBrush.Freeze(); 
			}
		}

		protected override void OnBarUpdate()
		{
			myPlot[0] = High[0];
			
			PlotBrushes[0][0] = myBrush;
			//Add your custom indicator logic here.
		}
		
		[Browsable(false)]
		[XmlIgnore()]
		public Series<double> myPlot
		{
			get { return Values[0]; }
		}
	}

If you are in fact just using a plain old .NET predefined Brush, the error would be unexpected but I'd need more details from your code to reproduce.

[strategesis]

Aha. That fixed it. I missed that when perusing the documentation. As a programmer for more than three decades, I think I already know everything, and so tend to skim instead of reading completely and thoroughly :-)

Suggestion: Add a section that provides a brief overview of the necessary (or recommended) differences between coding for NT7 and NT8 which result from the new multithreaded architecture for NT8. It mostly just needs to list each issue, and provide links to the various documentation pages which you already have (or will have) which discuss the details of each issue. And then link to the multithreading-issue overview section in the overview of the code-breaking changes for NT8.

[NinjaTrader_PaulH]

Hello strategesis,

Thanks for your suggestion. I have forward your suggestion as a feature request to Program Management for consideration.
We appreciate the feedback/suggestions to help us improve the Ninjatrader 8 Product.

[ninZa]

In Matthew's example above, is it necessary to call Freeze() if we use a predefined brush instead of a custom brush? See my comments below.

Thanks.

SolidColorBrush myBrush;

protected override void OnStateChange() {

if (State == State.SetDefaults) {

Description = @"Enter the description for your new custom Indicator here.";
Name = "MyCustomIndicator";
AddPlot(Brushes.Green, "myPlot");

} else if (State == State.Configure) {

myBrush = Brushes.Blue; // initiate it as a predefined brush instead
myBrush.Freeze(); // do we need to freeze the brush here?

}

}

protected override void OnBarUpdate() {

myPlot[0] = High[0];
PlotBrushes[0][0] = myBrush; //Add your custom indicator logic here.

}

[sledge]

Following the link and reading the documentation:

"Warning: If you do not call .Freeze() on a custom defined brush WILL eventually result in threading errors should you try to modify or access that brush after it is defined."

I would say NO. It's not necessary. But then again - I haven't used a brush yet!

Are you trying to change or modify it?

Are you seeing differences calling Freeze or not?

*I too will wait for official response on this.... too late to try testing here..

[ninZa]

Following the link and reading the documentation:

"Warning: If you do not call .Freeze() on a custom defined brush WILL eventually result in threading errors should you try to modify or access that brush after it is defined."

I would say NO. It's not necessary. But then again - I haven't used a brush yet!

Are you trying to change or modify it?

Are you seeing differences calling Freeze or not?

*I too will wait for official response on this.... too late to try testing here..

My guess is also "No". But I have tried using Freeze() also.

So far I have not seen any differences between calling and not calling Freeze() for predefined brush.

We need an official response on this.

[NinjaTrader_PaulH]

Hello,

Thanks for your posts on this topic.

Predefined brushes are static, cannot be modified and there is no need to Freeze() them.

[NinjaTrader_PaulH]

Hello,

To further assist, we have updated the NT8 helpguide documentation to clearly advise concerning predefined brushes.
Reference: http://ninjatrader.com/support/helpG...s/?brushes.htm (See first note in "Predefined brushes".

Thanks for your questions on this subject.

[ninZa]

Hello,

To further assist, we have updated the NT8 helpguide documentation to clearly advise concerning predefined brushes.
Reference: http://ninjatrader.com/support/helpG...s/?brushes.htm (See first note in "Predefined brushes".

Thanks for your questions on this subject.

Got it
Thank you for your great info and being so quick in updating the documentation.