AddLayer Widget
The AddLayer Widget for ArcGIS Web AppBuilder allows users to add pre-defined map layers to the current map without having them to include them in the current web map. This provides an easy way to add ad-hoc layers to your web app.
Unlike the AddService Widget which requires the user the enter the url of the service, the AddLayer widget only allows users to display additional map layers that have been pre-defined by the site administrator.
Using the Widget
The AddLayer Widget is an in-panel widget that will be displayed in the toolbar of your WebApp Builder application. Click the 
icon display the list of available layers. Click each layer you want to add to your map. These layers will be displayed on the map and may be toggled off or on using the standard LayerList widget. You can unclick the layers you do not want to show any more to remove them from the map.
Each entry is the list is pre-defined when the configuring the widget.
Widget Setup
Source code and installation instructions may be found at GitHub - softwhere/AddLayer-Widget:
v1.3.1 - released on 2/21/0216
Thanks to the City of Garland, Texas for sponsoring the initial development of the AddLayer Widget and releasing it to the community.
Portions of the configuration settings dialog for the AddLayer Widget were adapted from the configuration dialog of the excellent LocalLayer Widget .
Hi,
As an enhancement, would it be possible to include a fader control opaque to transparent next to the loaded layers (a similar function to the layerlist widget). Would be very useful for imagery layers and a more visible approach for the end user to find. Or is there another widget other than the layerlist widget that can provide this functionality already.
The problem with the layerlist widget in this workflow is that you cant control each layers settings, it's a global approach.
See screen shot below.
cheers
Rod
When you add a layer, the layerlist is updated but it post the layer name with its parent directory in the map service.
The widget LocalLayer widget has a similar issue that it can be resolved with a modification in the LayerInfos.js. The same solution does not resolve the issue in Add Layer.
Thanks.
UPDATE:
For those of you who would like to show just the name of the layer without the service name, in the folder: (app)\jimu.js\LayerInfos\LayerInfos.js
under the _getLayerTitle function:
comment out line 2 and add line 3.
if (title) {
//title = serviceName + " - " + title;
title=title;
} else {
title = serviceName;
} 
Well.. in a way, nevermind. I just realized instantly, this is actually not a problem at all. I simply have two user names for my secured services. One is a readonly user one is an editor. Guess what? I have the editor login access to all of them and readonly only accesses the MapServer versions of the layers. So editors login with their credential and read only viewers have a second login. Now, if someone was logged in to view, and wanted to Edit, they'd have to reload the site and enter the editing credential to reset the Esri identity. Not too bad. Simple solutions are always nice!! Hope this helps anyone in the same boat! 
