Registers a callback that's fired when a layer is selected.
Returns an ID which can be passed to unlisten() to unregister the callback.
| Usage | Returns | DrawingTools.onLayerSelect(callback) | String |
| Argument | Type | Details | this: ui.map.drawingtools | ui.Map.DrawingTools | The ui.Map.DrawingTools instance. |
callback | Function | The callback to fire when a shape is selected. The callback is passed two parameters: the selected GeometryLayer (or null for deselect) and the ui.Map.DrawingTools widget that the event listener is bound to. |