A few things worth checking:
- Are the coordinates in correct spatial reference? If they are in web mercator, you'll need to first project them into WGS 84, or pass in the Web Mercator sr when creating the point.
- Are the order of longitude and latitude correct? A common mistake is that the x-y and lon-lat are mismatched. Say if you pass in a latitude that is not in the range of (-90°, 90°), then the point is invalid and won't show as a graphic
- Are you adding the graphics overlays to the map view? It would be simpler to just add once
mapView.graphicsOverlays.add(graphicsOverlay)
and avoid adding the graphicsOverlay multiple times.
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Making slight change to your code and it works for me.
let point = AGSPoint(x: -118.41612, y: 33.37432, spatialReference: .wgs84())
let symbol = AGSSimpleMarkerSymbol(style: .diamond, color: .red, size: 28)
let graphic = AGSGraphic(geometry: point, symbol: symbol)
self.graphicsOverlay.graphics.add(graphic)
// Only add once for each graphics overlay.
self.mapView.graphicsOverlays.add(self.graphicsOverlay)