Steema Central

Posted: **Mon Nov 09, 2020 7:52 am**

I'm adding DrawLineItems to the Lines collection and that's fine --

Until the chart tries to refresh and throws an exception because all the "Handles" fields such as EndHandle, MidlleBottomHandle, MiddleTopHandle, and Starthandle are Null so a NullReferenceException is thrown.

My question is how to either populate the Handle values or avoid the exception when programmatically adding DrawLineItems to a .Net TeeChart?

Error

: Error.gif (52.58 KiB) Viewed 12161 times

My populate code:

: howtopopulate.gif (51.04 KiB) Viewed 12161 times

Null "Handle's" in DrawLineItems

: nullDrawLineItems.gif (48.27 KiB) Viewed 12161 times

Also when I add the line to the DrawLines Lines collection it doesn't throw the newline event like when I draw the line on the screen by hand with the mouse.

Thanks for your help.

Joseph

Posted: **Mon Nov 09, 2020 10:05 am**

Hello Joseph,

I think the reason is that you are using the parameterless constructor of DrawLineItem, which means that EndHandle will throw an error (following code is from the sourcecode):

Code: Select all

        public Rectangle EndHandle
        {
            get
            {
                return RectangleFromPoint(tool.AxisPoint(EndPos));
            }
        }

It will throw an error because the tool variable is null - this is the parameter you can pass in the other constructor of DrawLineItem, e.g.

Code: Select all

        private void InitializeChart(TChart chart)
        {
            chart.Series.Add(typeof(Line)).FillSampleValues();

            var drawLine = new DrawLine(chart.Chart);

            var item = new DrawLineItem(drawLine); //<-- pass in the 'tool' here
            item.Pen.Width = 3;
            item.Pen.Color = Color.Red;
            item.StartPos = new PointDouble(1, 1);
            item.EndPos = new PointDouble(3, chart.Series[0].YValues.Maximum);

            drawLine.Lines.Add(item);
        }

Posted: **Mon Nov 09, 2020 6:16 pm**

Christopher - u r correct! I feel dumb for missing the constructor that takes the drawline object as a param.

: fixed.gif (60.87 KiB) Viewed 12148 times

Thanks soooooo much!!!

Posted: **Tue Nov 10, 2020 8:51 am**

Hello Joseph!

jzarech wrote: ↑
Mon Nov 09, 2020 6:16 pm
Thanks soooooo much!!!

You are very welcome! Don't forget that debugging such issues is considerably easier with the source code

Steema Central

Programmatically Creating DrawLineItem Error Null Handles Exception

Programmatically Creating DrawLineItem Error Null Handles Exception

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Re: Programmatically Creating DrawLineItem Error Null Handles Exception

Re: Programmatically Creating DrawLineItem Error Null Handles Exception