Manage Operational Layers

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# Manage Operational Layers
Add, remove and reorder operational layers in a map.

![Manage Operational Layers App](manage-operational-layers.png)

## How to use the sample
Two map image layers are already added to the map in this sample. When you launch this sample you will see a MapView with a basemap and the two operational layers on it. When you press the 'Operational Layers' button the sample switches to the second activity where you will see two lists. One which shows all the operational layers added to the map and the other which shows the layers that have been removed from the map. In the Added Layers list you can tap and delete the layer from the map, or long press and change the order in which the layers are added on to the map. In the Removed Layers list you can tap and add the layer back to the map.

## How it works
`LayerList` represents the operational layers of an `ArcGISMap` or the base/reference layers of a `Basemap`. When the layers in the list are rendered in a `MapView`, the changes in the list have an immediate effect on how these layers are rendered in the `MapView`.

## Relevant API
* ArcGISMap
* ArcGISMapImageLayer
* MapView
* LayerList

Code

/* Copyright 2016 Esri
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package com.esri.arcgisruntime.sample.manageoperationallayers;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

import com.esri.arcgisruntime.geometry.Point;
import com.esri.arcgisruntime.geometry.SpatialReference;
import com.esri.arcgisruntime.layers.ArcGISMapImageLayer;
import com.esri.arcgisruntime.mapping.ArcGISMap;
import com.esri.arcgisruntime.mapping.Basemap;
import com.esri.arcgisruntime.mapping.LayerList;
import com.esri.arcgisruntime.mapping.Viewpoint;
import com.esri.arcgisruntime.mapping.view.MapView;

public class MainActivity extends AppCompatActivity {

  private static LayerList mOperationalLayers;
  private MapView mMapView;

  /**
   * returns the LayerList associated with the Map
   *
   * @return LayerList containing all the operational layers in the Map
   */
  public static LayerList getOperationalLayerList() {
    return mOperationalLayers;
  }

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    ArcGISMapImageLayer imageLayerElevation, imagelayerCensus;
    Button selectLayers;

    // inflate MapView from layout
    mMapView = (MapView) findViewById(R.id.mapView);

    // inflate operational layer selection button from the layout
    selectLayers = (Button) findViewById(R.id.operationallayer);

    // create a map with the BasemapType topographic
    ArcGISMap mMap = new ArcGISMap(Basemap.Type.TOPOGRAPHIC, 34.056295, -117.195800, 14);

    imageLayerElevation = new ArcGISMapImageLayer(getResources().getString(R.string.imagelayer_elevation_url));
    imagelayerCensus = new ArcGISMapImageLayer(getResources().getString(R.string.imagelayer_census_url));

    // get the LayerList from the Map
    mOperationalLayers = mMap.getOperationalLayers();
    // add operational layers to the Map
    mOperationalLayers.add(imageLayerElevation);
    mOperationalLayers.add(imagelayerCensus);

    // set the initial viewpoint on the map
    mMap.setInitialViewpoint(new Viewpoint(new Point(-133e5, 45e5, SpatialReference.create(3857)), 2e7));

    // set the map to be displayed in this view
    mMapView.setMap(mMap);

    selectLayers.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        Intent intent = new Intent(MainActivity.this, OperationalLayers.class);
        intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
        startActivity(intent);

      }
    });
  }

  @Override
  protected void onPause() {
    super.onPause();
    mMapView.pause();
  }

  @Override
  protected void onResume() {
    super.onResume();
    mMapView.resume();
  }

  @Override
  protected void onDestroy() {
    super.onDestroy();
    mMapView.dispose();
  }
}