What causes anchor.SlotIndex to evaluate to -1?

[forrestang]

Hello.

I am working within OnRender(), and attempting to find the location of various user drawn objects on the chart, and report the time, price, and specifically the bar location.

I am using Anchor.SlotIndex, rounding it, and then converting it to an int.

The odd thing is that it work some times. There are other times, where it seems to evaluate to -1. It does not seem to come from objects that are off the time scale, so I'm not sure WHERE this error is coming from?

I saw in the docs, somewhere speaking of -1, but I do not remember where it was?

Are there any known reasons why this would evaluate to -1?

Context of the foreach loop I am doing is attached.

[NinjaTrader_ChelseaB]

Hello forrestang,

Definitely do not do this in OnRender(). Do this in OnBarUpdate or any other method than OnRender().

A negative -1 index would imply to me that the anchor is not associated with a chart bar. Are you able to print the anchor.Time? Does this correspond with a bar on the chart?

[forrestang]

My script was simply one where it would record times/prices from manually drawn arrows I placed on a chart. I place two same direction arrows on each bar, representing an entry/stop price. I added logic to EXPECT two arrows per bar, and for some reason my script would find an arrow where I hadn't drawn one. Due to this expected logic, if there was not two arrows on the same bar, it would break.

I am using this on historical charts, usually w/no data connection, so I used onRender(), as onBarUpdate() requires an incoming tick to run once. So that's why I used onRender(), and created virtual bar series with Lists.

There was an option to create some type of button, and create logic to force it to run once, but I didn't want to go that route just yet.

I was getting intermittent behavior and it was difficult to isolate.

I.e., it would work fine, but upon a restart of the platform, or if I duplicated the chart to a new window... it would break.

The issue was indeed the bar index.

I managed to find where it was producing odd values, and due to the weird logic I had it would break occasionally. I added a check to ensure this value is never -1.