B4J Question Changing the fill colour of a jGoogleMaps polygon

Ralph Parkhurst · Nov 13, 2024

I'm trying to change the fill colour of an existing jGoogleMaps polygon, when it is clicked.

By studying the GmapsFX api documentation here I tried this code - but it failed to work:

B4X:

Private Sub GMap_PolygonClick (SelectedPolygon As MapPolygon)
    'change fill colour to green when the user clicks
    Private joFillColor = SelectedPolygon As JavaObject
    joFillColor = joFillColor.InitializeNewInstance("com.lynden.gmapsfx.shapes.Polygon", Null)
    joFillColor = joFillColor.RunMethod("setProperty", Array As Object("fillColor", Array As Object(fx.Colors.Green)))
End Sub

Where have I gone wrong?

Best regards,
Ralph

DonManfred · Nov 13, 2024

Do you get any error?

Ralph Parkhurst said:
joFillColor = joFillColor.InitializeNewInstance("com.lynden.gmapsfx.shapes.Polygon", Null)

try to remove that line. You are creating a NEW Polygon here overwriting the existing.
InitializeNewInstance will create a new one with zero properties set and even this Polygon is not added to your GoogleMap too.
Setting a color to it will have no effect.

Ralph Parkhurst · Nov 13, 2024

DonManfred said:
Do you get any error?

No error is reported at all. And the polygon fill colour did not change.

DonManfred said:
try to remove that line.

Thanks for that suggestion, however unfortunately it did not help - again no error reported and no colour change.

DonManfred · Nov 13, 2024

You probably have to create a new PolygonOptions object and set the Fillcolor here.
replace the PolygonOptions in the Polygon then. But there is not method to set a new PolygonOptions.

Guess you have to remember the PolygonOptions you use when filling the Map.

Change the right PolygonOptions for the Polygon clicked.

Ralph Parkhurst · Nov 13, 2024

DonManfred said:
You probably have to create a new PolygonOptions object and set the Fillcolor here.
replace the PolygonOptions in the Polygon then. But there is not method to set a new PolygonOptions.

Guess you have to remember the PolygonOptions you use when filling the Map.

Change the right PolygonOptions for the Polygon clicked.

That sounds like a good suggestion. It might be a bit beyond my current understanding, but I will give it a shot and report back. And if nothing else I will learn along the way.

DonManfred · Nov 13, 2024

Ralph Parkhurst said:
It might be a bit beyond my current understanding

post the code you use to create the polygon and adding them to the map.

I have to add that i never used GoogleMaps in B4J, only B4A.

Ralph Parkhurst · Nov 13, 2024

Yes, there do seem to be some differences between B4A and J when it comes to implementation of Google Maps.

Here is the code I used to add the initial polygon:

B4X:

gmap.AddPolygon(lstPointsLatLng, LineWidthPolygon, LineColorPolygon, FillColorPolygon, OpacityPolygon)

where my variables are:
lstPointsLatLng is a list of LatLng coordinates,
LineWidthPolygon is the stroke width,
LineColorPolygon is the stroke colour,
FillColorPolygon is the Fill Color, and
OpacityPolygon is the Opacity.

One other way I thought of is to create two polygons, each with a different colour. Then alternate their visibility when the user clicks. I've tested that this works, however will require some more effort to manage the extra polygons.

DonManfred · Nov 13, 2024

Ralph Parkhurst said:
Here is the code I used to add the initial polygon

i already thought so. I checked the Library code.

The PolygonOptions is used internally but you do not have access to it.

B4J/Libs_GoogleMaps/src/anywheresoftware/b4j/googlemaps/GoogleMapWrapper.java at master · AnywhereSoftware/B4J

B4J core libraries. Contribute to AnywhereSoftware/B4J development by creating an account on GitHub.

github.com

Starting at line 523

B4X:

/**
     * Adds a polygon to the map.
     *Points - A list or array of LatLng points.
     *StrokeWidth - Stroke width.
     *StrokeColor - Stroke color.
     *FillColor - Inner color.
     *Opacity - Inner color opacity. Value between 0 to 1.
     */
    public PolygonWrapper AddPolygon(List Points, float StrokeWidth, Paint StrokeColor, Paint FillColor, double Opacity)
    {
        PolygonOptions po = new PolygonOptions();
        po.strokeWeight(StrokeWidth);
        po.fillColor(htmlColor(FillColor));
        po.strokeColor(htmlColor(StrokeColor));
        po.fillOpacity(Opacity);
        boolean eventExist = ba.subExists(eventName + "_polygonclick");
        if (eventExist == false)
            po.clickable(false);
        po.paths(new MVCArray(Points.getObject().toArray()));
        Polygon gon = new Polygon(po);
        map.addMapShape(gon);
        if (eventExist) {
            map.addUIEventHandler(gon, UIEventType.click, new UIEventHandler() {
                @Override
                public void handle(JSObject obj) {
                    ba.raiseEventFromUI(GoogleMapWrapper.this, eventName + "_polygonclick",
                            (PolygonWrapper)AbsObjectWrapper.ConvertToWrapper(new PolygonWrapper(), gon));
                }
            });
        }
        return (PolygonWrapper)AbsObjectWrapper.ConvertToWrapper(new PolygonWrapper(), gon);

    }

I guess one have to change the library to add the possibility to access the PolygonOptions.

TILogistic · Nov 13, 2024

options see:

GoogleMapsDemo

Some time ago I played a lot with GoogleMaps according to this post: https://www.b4x.com/android/forum/threads/problem-with-googlemaps-handling-polygons.84238/#post-533844 The problem was to add other shapes on a googlemap overlapping existing shapes. When you move the mouse over an existing...

www.b4x.com

klaus · Nov 13, 2024

The GoogleMaps demo in the link in the previous post does not have the possibility to change the color of a polygon.
I have also searched for a solution and came to the same conclusion as DonManfred.

Ralph Parkhurst · Nov 13, 2024

Thank you everyone. The method I am currently using is actually based on your idea Klaus - using Canvas to overlay a border in a different colour. But I thought if I could directly change the fill colour of the polygon all would be easier (and nicer!). I think I will pursue Plan-B - two polygons with different fill colours, and switch visibility. If this creates a workable and manageable solution I will revert back with my finding.

Warm regards,
Ralph

TILogistic · Nov 13, 2024

It's because I suggested the link above, it's because it has a lot of logic to work with polygons with canvas.

In the click event you can see the logic of how to handle polygons.

Regards.

Ralph Parkhurst · Nov 14, 2024

TILogistic said:
In the click event you can see the logic of how to handle polygons.

Great insight - thank you. I will study this closely.

B4J Question Changing the fill colour of a jGoogleMaps polygon

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B4J/Libs_GoogleMaps/src/anywheresoftware/b4j/googlemaps/GoogleMapWrapper.java at master · AnywhereSoftware/B4J

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