Getting a null exception when i get the length of the line using C#?

Question

I am trying to get the length of a drawn line to a textbox but its throwing an NullReferenceException at var length = f.ToShape().ToGeometry().Length;. How to fix this Exception. what mistake i am making? Although i am using GIS library but i think its a problem related to C# thats why i am posting the question here rather in GIS section.

Code:

private void map1_MouseClick_1(object sender, MouseEventArgs e)
    {
        // digitizing
        if (amDigitizing == true)
        {
            DotSpatial.Topology.Coordinate c = new DotSpatial.Topology.Coordinate();
            System.Drawing.Point p = new System.Drawing.Point();
            p.X = e.X;
            p.Y = e.Y;
            c = map1.PixelToProj(p);

            myDigitizedPoints.Add(c);
        }
    }
    private void map1_MouseDoubleClick_1(object sender, MouseEventArgs e)
    {
        // Double click ends digitizing
        if (amDigitizing == true)
        {
            DotSpatial.Topology.Coordinate c = new DotSpatial.Topology.Coordinate();
            System.Drawing.Point p = new System.Drawing.Point();
            p.X = e.X;
            p.Y = e.Y;
            c = map1.PixelToProj(p);
            myDigitizedPoints.Add(c);

            amDigitizing = false;


            DotSpatial.Data.Feature f = new DotSpatial.Data.Feature(DotSpatial.Topology.FeatureType.Line, myDigitizedPoints);
            DotSpatial.Data.FeatureSet fs = new DotSpatial.Data.FeatureSet();
            fs.AddFeature(f);

            fs.Projection = map1.Projection;
            fs.Name = "Mine";
            //fs.SaveAs(GraphicsPathExt, true);
            //LineLyr = (DotSpatial.Controls.MapLineLayer)map1.AddLayer(GraphicsPathExt);
            LineLyr = (MapLineLayer)map1.Layers.Add(fs);

            var length = f.ToShape().ToGeometry().Length;
            textBox1.Text = length.ToString();
        }


    }

Simply enough, why dont you just check if f is null then check if ToShape returns null then check if ToGeometry returns null — misha130, May 08 '15 at 23:38
The code you posted does not show the error you describe. It should not be possible for `new` to return `null`; I suspect code you have not shown us is changing it. You have to use a debugger to track this down as shown in [What is a NullReferenceException](http://stackoverflow.com/questions/4660142/). — Dour High Arch, May 09 '15 at 00:24

MRebai · Accepted Answer · 2015-05-08T23:57:58.060

2

To fix your exception just add some test :

if(f != null) 
{
    var shape = f.ToShape();
    if(shape != null)
    {
       var geomtry = shape..ToGeometry();
       if(geomtry != null)
          var length = geomtry.Length; 
    }
}

edited May 08 '15 at 23:57

answered May 08 '15 at 23:41

MRebai

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try with this if(f != null){ /* Codes */} – user1924375 May 08 '15 at 23:45
The f couldn't be null since he create it at the code that he provide – MRebai May 08 '15 at 23:46
its not doing me any good. – Vanadium90 May 08 '15 at 23:50
its not doing me any good. – Vanadium90 May 08 '15 at 23:50
plz tell me where the exception happened at which line – MRebai May 08 '15 at 23:51
right at the first line 'var shape = f.ToShape();' – Vanadium90 May 08 '15 at 23:55
Can you try with the new code i added an tell me what happened – MRebai May 08 '15 at 23:58
its still throwing exception at var shape. . i think its the problem with To.Shape() function – Vanadium90 May 09 '15 at 01:12
then add the try catch block and check your exception to verify the error – MRebai May 09 '15 at 01:29

Getting a null exception when i get the length of the line using C#?

1 Answers1