Add a feature layer from a portal item

Learn how to use an ArcGIS portal item to access and display a feature layer in a map.

You can host a variety of geographic data and other resources using ArcGIS Online. These portal items can also define how the data is presented. A web map or web scene, for example, not only defines the layers for a map or scene, but also how layers are symbolized, the minimum and/or maximum scales at which they display, and several other properties. Likewise, a hosted feature layer contains the data for the layer and also defines the symbols and other display properties for how it is presented. When you add a map, scene, or layer from a portal item to your app, everything that has been saved with the item is applied in your app. Adding portal items to your app rather than creating them programmatically saves you from writing a lot of code, and can provide consistency across apps that use the same data.

In this tutorial, you will add a hosted feature layer to display trailheads in the Santa Monica Mountains of Southern California. The hosted layer defines the trailhead locations (points) as well as the symbols used to display them.

Prerequisites

Steps

Open the Visual Studio solution

1. To start the tutorial, complete the Display a map tutorial or download and unzip the solution.

2. Open the .sln file in Visual Studio.

3. If you downloaded the solution project, set your API key.

   Instructions for setting the API key

   An API Key enables access to services, web maps, and web scenes hosted in ArcGIS Online.

   If necessary, set the  API Key.

   1. Go to your developer dashboard to get your API key. For these tutorials, use your default API key. It is scoped to include all of the services demonstrated in the tutorials.

   2. In Visual Studio, in the Solution Explorer, click App.xaml.cs.

   3. In the App class, add an override for the OnStartup() function to set the ApiKey property on ArcGISRuntimeEnvironment.

      App.xaml.cs

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          public partial class App : Application
          {
      
              protected override void OnStartup(StartupEventArgs e)
              {
                  base.OnStartup(e);
                  // Note: it is not best practice to store API keys in source code.
                  // The API key is referenced here for the convenience of this tutorial.
                  Esri.ArcGISRuntime.ArcGISRuntimeEnvironment.ApiKey = "YOUR_API_KEY";
              }
      
          }
      }

Update the tutorial name used in the project (optional)

The Visual Studio solution, project, and the namespace for all classes currently use the name DisplayAMap. Follow the steps below if you prefer the name to reflect the current tutorial. These steps are not required, your code will still work if you keep the original name.

Display the ArcGIS portal item

You can reference an item (such as a web map or feature layer) hosted in a portal (such as ArcGIS Online) using its unique item ID. You will reference the Trailheads Styled feature layer stored in ArcGIS Online using its item ID of: 2e4b3df6ba4b44969a3bc9827de746b3. You will then add that feature layer to your map's collection of data layers (operational layers).

1. In Visual Studio, in the Solution Explorer, double-click MapViewModel.cs to open the file.

2. Add additional required using statements near the top of the class file.

   MapViewModel.cs

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   using System;
   using System.Collections.Generic;
   using System.Text;
   using Esri.ArcGISRuntime.Geometry;
   using Esri.ArcGISRuntime.Mapping;
   using System.ComponentModel;
   using System.Runtime.CompilerServices;
   
   using Esri.ArcGISRuntime.Portal;
   using System.Threading.Tasks;
   

3. Modify the signature of the SetupMap() function to include the async keyword and to return Task rather than void.

   MapViewModel.cs

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           private async Task SetupMap()
           {
   
               // Create a new map with a 'topographic vector' basemap.
               Map = new Map(BasemapStyle.ArcGISTopographic);
   
   
           }
   
   More info

   When calling methods asynchronously inside a function (using the await keyword), the async keyword is required in the signature.

   Although a void return type would continue to work, this is not considered best practice. Exceptions thrown by an async void method cannot be caught outside of that method, are difficult to test, and can cause serious side effects if the caller is not expecting them to be asynchronous. The only circumstance where async void is acceptable is when using an event handler, such as a button click.

   See the Microsoft documentation for more information about Asynchronous programming with async and await.

4. In the MapViewModel constructor, modify the call to SetupMap() to avoid a compilation warning. After changing SetupMap() to an asynchronous method, the following warning appears in the Visual Studio Error List.

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   Because this call is not awaited, execution of the current method continues before the call is
   completed. Consider applying the 'await' operator to the result of the call.

   Because your code does not anticipate a return value from this call, the warning can be ignored. To be more specific about your intentions with this call and to address the warning, add the following code to store the return value in a discard.

   MapViewModel.cs

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           public MapViewModel()
           {
   
               _ = SetupMap();
   
           }
   
   More info

   From the Microsoft documentation:

   "[Discards] are placeholder variables that are intentionally unused in application code. Discards are equivalent to unassigned variables; they don't have a value. A discard communicates intent to the compiler and others that read your code: You intended to ignore the result of an expression."

5. Add code to the SetupMap() function to create a PortalItem object that references the feature layer portal item. To do this, provide the item ID and an ArcGISPortal object.

   MapViewModel.cs

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           private async Task SetupMap()
           {
   
               // Create a new map with a 'topographic vector' basemap.
               Map = new Map(BasemapStyle.ArcGISTopographic);
   
   
               // Create an ArcGIS Portal object.
               ArcGISPortal portal = await ArcGISPortal.CreateAsync();
   
               // Create a portal item from the ArcGIS Portal object using a portal item string.
               PortalItem portalItem = await PortalItem.CreateAsync(portal, "2e4b3df6ba4b44969a3bc9827de746b3");
   
           }
   

6. Create a FeatureLayer using the PortalItem which loads it asynchronously. Then add the feature layer to the Map's operational layers collection.

   MapViewModel.cs

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           private async Task SetupMap()
           {
   
               // Create a new map with a 'topographic vector' basemap.
               Map = new Map(BasemapStyle.ArcGISTopographic);
   
   
               // Create an ArcGIS Portal object.
               ArcGISPortal portal = await ArcGISPortal.CreateAsync();
   
               // Create a portal item from the ArcGIS Portal object using a portal item string.
               PortalItem portalItem = await PortalItem.CreateAsync(portal, "2e4b3df6ba4b44969a3bc9827de746b3");
   
               // Create a feature layer from the portal item and specify a numerical layer id (i.e. 0).
               FeatureLayer layer = new FeatureLayer(portalItem, 0);
   
               // Add the layer to the operational layer of the map.
               Map.OperationalLayers.Add(layer);
   
           }
   

   Expand

7. Click Debug > Start Debugging (or press <F5> on the keyboard) to run the app.

You should see a map of trail heads in the Santa Monica mountains. Click, drag, and scroll the mouse wheel on the map view to explore the map.

What's next?

Learn how to use additional API features, ArcGIS location services, and ArcGIS tools in these tutorials:

• Display a web map
• Display a web scene