How to toggle ArcGIS webmap layers using ArcGIS Javascript API

Question

I've created a webmap using ArcGIS Online that I want to render in a web app using the ArcGIS for Javascript API. In ArcGIS Online, I've saved the webmap with all of the layers off (visibility: false). I want set the visibility of one layer ("Layer X" below) to true using the API.

    arcgisUtils.createMap(mapid, "map").then(function(response){

         layers = response.itemInfo.itemData.operationalLayers;

         dojo.forEach(layers, function(layer){

             if (layer.title == 'Layer X') {
                 layer.setVisibility(true)**;
             }
             console.log(layer.title + ", visibility: " + layer.visibility);

         });

     });

**I've tried using .show() as well.

Using the code snippet above, the visibility of "Layer X" doesn't change. The console log reports the layer title & visibility of all the layers except the one I'm trying to show.

The response object returned from the .createMap method is a Deferred object.

Is it possible to toggle the layers of a webmap using the ArcGIS for Javascript API, or is the response object immutable?

Answer 1

The layer object returned via the createMap response doesn't have the property "setVisibility."

However, it does has a property called "layerObject," which seems to be the actual map object. The code snippet below does the trick:

 layer.layerObject.setVisibility(true)

Answer 2

In this situation I think the problem is that you are attempting to dig your layer out of the response itemInfo as opposed to the actual response map.

from this sample...

var myLayer = map.getLayer("USA_Tapestry_335");
myLayer.setVisibility(false);

Answer 3

Another way to get the layers in the webmap is through arcgisUtils.getLegendLayers(). It generates a list of objects that include the title from ArcGIS Online, and the layer. Here's a snippet of what I would use accomplish what you're looking for.

arcgisUtils.createMap(mapid, "map").then(function(response){

     var legendLayers = arcgisUtils.getLegendLayers(response);

     dojo.forEach(legendLayers, function (item) {
         if (item.title === "Layer X") {
           item.layer.setVisibility(true);
         }
     });

 });