Gmap.net can't show multi markers use C# winform

Question

I want show multi marker on Map , but seem can't , code follow : button1_Click show Position ,button2_Click show markers ! anyone give me any instructions? thanks.

 private void button1_Click(object sender, EventArgs e)
 {

    gmap.DragButton = MouseButtons.Left;
    gmap.MapProvider = GMapProviders.GoogleMap;
    gmap.Position = new PointLatLng(25.037531, 121.5639969);
    gmap.MinZoom = 5;
    gmap.MaxZoom = 100;
    gmap.ShowCenter = false;
    gmap.Zoom = 15;
 }
 private void button2_Click(object sender, EventArgs e)
 {
        Random r = new Random();

        var marker = new GMarkerGoogle(new PointLatLng(r.Next(25, 500), 121), GMarkerGoogleType.green);
        var marker1 = new GMarkerGoogle(new PointLatLng(r.Next(25, 500), 121), GMarkerGoogleType.pink);
        var marker2 = new GMarkerGoogle(new PointLatLng(r.Next(25, 500), 121), GMarkerGoogleType.blue);
        var marker3 = new GMarkerGoogle(new PointLatLng(r.Next(25, 500), 121), GMarkerGoogleType.yellow);
        marker.IsVisible = true; marker1.IsVisible = true; marker2.IsVisible = true; marker3.IsVisible = true;

        gMapOverlay.Markers.Add(marker); 
        gMapOverlay.Markers.Add(marker1);
        gMapOverlay.Markers.Add(marker2); 
        gMapOverlay.Markers.Add(marker3);
        gmap.Overlays.Add(gMapOverlay);  
   }

What does the code do now? What do you want it to do instead? — mjwills, Apr 07 '18 at 10:35
If you put a breakpoint on the `Random` line, does it get hit? — mjwills, Apr 08 '18 at 05:47

score 0 · Answer 1 · answered Apr 15 '18 at 12:57

Your code is ok, but the problem with the random function that you use only generates integers, and a small change as 1 integer means changing a complete degree in either latitude or longitude and this is a hudge displacement.

So you have to generate a random Doubles number instead of Integers.

I edit the code to work correctly.

using GMap.NET;
using GMap.NET.WindowsForms.Markers;

public class Form1
{

    private GMap.NET.WindowsForms.GMapOverlay gMapOverlay;
    private Random rand = new Random();

    private void Form1_Load(object sender, EventArgs e)
    {

        GMapControl1.DragButton = MouseButtons.Left;
        GMapControl1.MapProvider = GMap.NET.MapProviders.GMapProviders.GoogleMap;
        GMapControl1.Position = new PointLatLng(25.037531, 121.5639969);
        GMapControl1.MinZoom = 5;
        GMapControl1.MaxZoom = 20;
        GMapControl1.ShowCenter = false;
        GMapControl1.Zoom = 11;

        gMapOverlay = new WindowsForms.GMapOverlay("markers");
        gMapOverlay.IsVisibile = true;

    }

    private void button2_Click(object sender, EventArgs e)
    {

        var marker = new GMarkerGoogle(new PointLatLng(GetRandomDouble(24.8, 25.1), GetRandomDouble(121.3, 121.6)), GMarkerGoogleType.green);
        var marker1 = new GMarkerGoogle(new PointLatLng(GetRandomDouble(24.8, 25.1), GetRandomDouble(121.3, 121.6)), GMarkerGoogleType.pink);
        var marker2 = new GMarkerGoogle(new PointLatLng(GetRandomDouble(24.8, 25.1), GetRandomDouble(121.3, 121.6)), GMarkerGoogleType.blue);
        var marker3 = new GMarkerGoogle(new PointLatLng(GetRandomDouble(24.8, 25.1), GetRandomDouble(121.3, 121.6)), GMarkerGoogleType.yellow);

        marker.IsVisible = true;
        marker1.IsVisible = true;
        marker2.IsVisible = true;
        marker3.IsVisible = true;

        //   Clear old markers
        gMapOverlay.Markers.Clear();

        gMapOverlay.Markers.Add(marker);
        gMapOverlay.Markers.Add(marker1);
        gMapOverlay.Markers.Add(marker2);
        gMapOverlay.Markers.Add(marker3);

        //   Clear old overlay
        GMapControl1.Overlays.Clear();
        GMapControl1.Overlays.Add(gMapOverlay);

        //   Zoom the map to show all drawn markers
        GMapControl1.ZoomAndCenterMarkers(gMapOverlay.Id);
    }

    public double GetRandomDouble(double min, double max)
    {
        return rand.NextDouble() * (max - min) + min;
    }

Gmap.net can't show multi markers use C# winform

1 Answers1