topic How to use Where clauses in labeldefinition in ArcGIS Runtime SDK for Android Questions

How to use Where clauses in labeldefinition

NathanMellor — Sat, 11 Dec 2021 14:06:07 GMT

I was trying out some label definitions in Android on a GraphicsOverlay


static final String labelPolygon = "{" +
        "\"labelExpressionInfo\": {" + // Define a labeling expression that will show the address attribute value
        "\"expression\": \"return $feature.geometryName;\"}," +
        "\"labelPlacement\": \"esriServerPolygonPlacementAlwaysHorizontal\"," + // Align labels horizontally
        "\"where\": \"$feature.geometryType='Polygon'\"}," +
        "\"symbol\": {" + // Use a black bold text symbol
        "\"color\": [0,0,0,255]," +
        "\"haloColor\": [255,255,255,96]," +
        "\"haloSize\": 2," +

        "\"font\": {\"size\": 10}," +
        "\"type\": \"esriTS\"}" +
        "}";

static final String labelPolyline = "{" +
        "\"labelExpressionInfo\": {" + // Define a labeling expression that will show the address attribute value
        "\"expression\": \"return $feature.geometryName;\"}," +
         "\"where\": \"$feature.geometryType='Polyline'\"}," +
        "\"labelPlacement\": \"esriServerLinePlacementAboveAlong\"," + // Align labels horizontally
        "\"symbol\": {" + // Use a black bold text symbol
        "\"color\": [0,0,0,255]," +
        "\"haloColor\": [255,255,255,96]," +
        "\"haloSize\": 2," +
        "\"font\": {\"size\": 10}," +
        "\"type\": \"esriTS\"}" +
        "}";

static final String labelPoint = "{" +
        "\"labelExpressionInfo\": {" + // Define a labeling expression that will show the address attribute value
        "\"expression\": \"return $feature.geometryName;\"}," +
        "\"where\": \"$feature.geometryType='Point'\"}," +
        "\"labelPlacement\": \"esriServerPointLabelPlacementBelowCenter\"," + // Align labels horizontally
        "\"symbol\": {" + // Use a black bold text symbol
        "\"color\": [0,0,0,255]," +
        "\"haloColor\": [255,255,255,96]," +
        "\"haloSize\": 2," +
        "\"font\": {\"size\": 10}," +
        "\"type\": \"esriTS\"}" +
        "}";

I thought perhaps that since they have a rule for polygon, polyline, and point, that they would

That wasn't the case, and I got too many labels. I get one below and above a point symbol. 

I tried adding "where" clause to restrict the polygon labels to polygons and so forth. 
Then all labels dissappear. 

I have found little to no guidance on what syntax should be followed in a where clause. I don't even know if it is SQL
or an Arcade Expression.

Re: How to use Where clauses in labeldefinition

XanderBakker — Sat, 13 Oct 2018 19:47:06 GMT

In Arcade you have the TypeOf that will allow you to detect these types: Array, Date, String, Boolean, Number, Dictionary, Feature, Point, Polygon, Polyline, Multipoint, Extent, Function, Unrecognized Type

Data Functions | ArcGIS for Developers

Re: How to use Where clauses in labeldefinition

NathanMellor — Sat, 13 Oct 2018 22:25:12 GMT

So then what would be the complete syntax?

Any example?

         "\"where\": \"TypeOf($feature.geometry)='Polyline'\"}," +

Re: How to use Where clauses in labeldefinition

NathanMellor — Sat, 11 Dec 2021 14:06:10 GMT

No luck.

Tried:

         "\"where\": \"TypeOf($feature)=='Polyline'\"}," +
Tried: 
          "\"where\": \"TypeOf($feature)==Polyline\"}," +

Sorry to be dense, but to do this, I will need an exact example.

Re: How to use Where clauses in labeldefinition

XanderBakker — Sat, 11 Dec 2021 14:06:13 GMT

I am not a programmer, but what I understand is that you are trying to construct the json for the labelExpressionInfo. If I manually set the label expression in a web map, with this (just to see if it can detect the type of geometry in the label expression):

if (TypeOf(Geometry($feature)) == 'Polygon') {
    return "A Polygon";
} else if (TypeOf(Geometry($feature)) == 'Polyline') {
    return "A Polyline";
} else if (TypeOf(Geometry($feature)) == 'Point') {
    return "A Point";
} else {
    return "Unknown";
}‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

... it will create this json section:

"labelExpressionInfo": {
                                "expression": "if (TypeOf(Geometry($feature)) == 'Polygon') {\n    return \"A Polygon\";\n} else if (TypeOf(Geometry($feature)) == 'Polyline') {\n    return \"A Polyline\";\n} else if (TypeOf(Geometry($feature)) == 'Point') {\n    return \"A Point\";\n} else {\n    return \"Unknown\"\n}"
                            }‍‍‍