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

Before starting this tutorial:

You need an ArcGIS Location Platform or ArcGIS Online account.
Ensure your development environment meets the system requirements.

Optionally, you may want to install the ArcGIS Maps SDK for .NET to get access to project templates in Visual Studio (Windows only) and offline copies of the NuGet packages.

Develop or download

You have two options for completing this tutorial:

Option 1: Develop the code or
Option 2: Download the completed solution

Option 1: Develop the code

To start the tutorial, complete the Display a map tutorial. This creates a map to display the Santa Monica Mountains in California using the topographic basemap from the ArcGIS basemap styles service.

Open a Visual Studio solution

Open the Visual Studio solution you created by completing the Display a map tutorial.
Continue with the following instructions to display a feature layer hosted in an ArcGIS portal in your map.

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.

The tutorial instructions and code use the name AddAFeatureLayerFromAPortalItem for the solution, project, and namespace. You can choose any name you like, but it should be the same for each of these.

Update the name for the solution and the project.
- In Visual Studio, in the Solution Explorer, right-click the solution name and choose Rename. Provide the new name for your solution.
- In the Solution Explorer, right-click the project name and choose Rename. Provide the new name for your project.
Rename the namespace used by classes in the project.
- In the Solution Explorer, expand the project node.
- Double-click MapViewModel.cs in the Solution Explorer to open the file.
- In the MapViewModel class, double-click the namespace name (DisplayAMap) to select it, and then right-click and choose Rename....
- Provide the new name for the namespace.
- Click Apply in the Rename: DisplayAMap window that appears in the upper-right of the code window. This will rename the namespace throughout your project.
Build the project.
- Choose Build > Build solution (or press <F6>).

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).

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

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

MapViewModel.cs
Use dark colors for code blocks
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;

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.
            var map = new Map(BasemapStyle.ArcGISTopographic);

            // Set the initial viewpoint around the Santa Monica Mountains in California.
            var mapCenterPoint = new MapPoint(-118.805, 34.027, SpatialReferences.Wgs84);
            map.InitialViewpoint = new Viewpoint(mapCenterPoint, 100000);

            // Set the view model's Map property with the map.
            Map = map;

        }

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.

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.
Use dark colors for code blocksCopy
```
1
2
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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```
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        public MapViewModel()
        {

            _ = SetupMap();

        }
```
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."

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
Use dark colors for code blocks
        private async Task SetupMap()
        {

            // Create a new map with a 'topographic vector' basemap.
            var map = new Map(BasemapStyle.ArcGISTopographic);

            // Set the initial viewpoint around the Santa Monica Mountains in California.
            var mapCenterPoint = new MapPoint(-118.805, 34.027, SpatialReferences.Wgs84);
            map.InitialViewpoint = new Viewpoint(mapCenterPoint, 100000);

            // Set the view model's Map property with the map.
            Map = map;

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

MapViewModel.cs
Expand
Use dark colors for code blocks
        private async Task SetupMap()
        {

            // Create a new map with a 'topographic vector' basemap.
            var map = new Map(BasemapStyle.ArcGISTopographic);

            // Set the initial viewpoint around the Santa Monica Mountains in California.
            var mapCenterPoint = new MapPoint(-118.805, 34.027, SpatialReferences.Wgs84);
            map.InitialViewpoint = new Viewpoint(mapCenterPoint, 100000);

            // Set the view model's Map property with the map.
            Map = map;

            // 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

Click Debug > Start Debugging (or press <F5> on the keyboard) to run the app. If your app uses user authentication, enter your ArcGIS Online credentials when prompted.

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.

Alternatively, you can download the tutorial solution, as follows.

Option 2: Download the solution

Click the Download solution link in the right-hand panel of the page.
Unzip the file to a location on your machine.
Open the .sln file in Visual Studio.

Since the downloaded solution does not contain authentication credentials, you must first set up authentication to create credentials, and then add the developer credentials to the solution.

Set up authentication

To access the secure ArcGIS location services used in this tutorial, you must implement API key authentication or user authentication using an ArcGIS Location Platform or an ArcGIS Online account.

You can implement API key authentication or user authentication in this tutorial. Compare the differences below:

API key authentication

Users are not required to sign in.
Requires creating an API key credential with the correct privileges.
API keys are long-lived access tokens.
Service usage is billed to the API key owner/developer.
Simplest authentication method to implement.
Recommended approach for new ArcGIS developers.

Learn more in API key authentication.

User authentication

Users are required to sign in with an ArcGIS account.
User accounts must have privilege to access the ArcGIS services used in application.
Requires creating OAuth credentials.
Application uses a redirect URL and client ID.
Service usage is billed to the organization of the user signed into the application.

Learn more in User authentication.

Create a new API key access token with privileges to access the secure resources used in this tutorial.

Complete the Create an API key tutorial and create an API key with the following privilege(s):
- Privileges
  - Location services > Basemaps
Copy and paste the API key access token into a safe location. It will be used in a later step.

Create new OAuth credentials to access the secure resources used in this tutorial.

Complete the Create OAuth credentials for user authentication tutorial to obtain a Client ID and Redirect URL.

A Client ID uniquely identifies your app on the authenticating server. If the server cannot find an app with the provided Client ID, it will not proceed with authentication.
The Redirect URL (also referred to as a callback url) is used to identify a response from the authenticating server when the system returns control back to your app after an OAuth login. Since it does not necessarily represent a valid endpoint that a user could navigate to, the redirect URL can use a custom scheme, such as my-app://auth. It is important to make sure the redirect URL used in your app's code matches a redirect URL configured on the authenticating server.
Copy and paste the Client ID and Redirect URL into a safe location. They will be used in a later step.

All users that access this application need account privileges to access the ArcGIS Basemap Styles service.

Set developer credentials in the solution

To allow your app users to access ArcGIS location services, use the developer credentials that you created in the Set up authentication step to authenticate requests for resources.

In Visual Studio, in the Solution Explorer, click App.xaml.cs to open the file.

Set the ArcGISEnvironment.ApiKey property with your API key access token.

App.xaml.cs
Use dark colors for code blocks
        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);

            // Set the access token for ArcGIS Maps SDK for .NET.
            Esri.ArcGISRuntime.ArcGISRuntimeEnvironment.ApiKey = "YOUR_ACCESS_TOKEN";

            // Call a function to set up the AuthenticationManager for OAuth.
            UserAuth.ArcGISLoginPrompt.SetChallengeHandler();

        }

Remove the code that sets up user authentication.

App.xaml.cs
Use dark colors for code blocks
        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);

            // Set the access token for ArcGIS Maps SDK for .NET.
            Esri.ArcGISRuntime.ArcGISRuntimeEnvironment.ApiKey = "YOUR_ACCESS_TOKEN";

            // Call a function to set up the AuthenticationManager for OAuth.
            UserAuth.ArcGISLoginPrompt.SetChallengeHandler();

        }

Best Practice: The access token is stored directly in the code as a convenience for this tutorial. Do not store credentials directly in source code in a production environment.

From the Visual Studio Solution explorer window, open the ArcGISLoginPrompt.cs file.

Set your values for the client ID (OAuthClientID) and the redirect URL (OAuthRedirectUrl). These are the user authentication settings you created in the Set up authentication step.

ArcGISLoginPrompt.cs
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    internal static class ArcGISLoginPrompt
    {
        private const string ArcGISOnlineUrl = "https://www.arcgis.com/sharing/rest";
        // Specify the Client ID and Redirect URL to use with OAuth authentication.
        // See the instructions here for creating OAuth app settings:
        // https://developers.arcgis.com/documentation/security-and-authentication/user-authentication/tutorials/create-oauth-credentials-user-auth/

        private const string AppClientId = "YOUR_CLIENT_ID";
        private const string OAuthRedirectUrl = "YOUR_REDIRECT_URL";

In Visual Studio, in the Solution Explorer, click App.xaml.cs to open the file.

Remove the line of code that sets an API key access token.

App.xaml.cs
Use dark colors for code blocks
        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);

            // Set the access token for ArcGIS Maps SDK for .NET.
            Esri.ArcGISRuntime.ArcGISRuntimeEnvironment.ApiKey = "YOUR_ACCESS_TOKEN";

            // Call a function to set up the AuthenticationManager for OAuth.
            UserAuth.ArcGISLoginPrompt.SetChallengeHandler();

        }

Best Practice: The OAuth credentials are stored directly in the code as a convenience for this tutorial. Do not store credentials directly in source code in a production environment.

Run the solution

Click Debug > Start Debugging (or press <F5> on the keyboard) to run the app. If your app uses user authentication, enter your ArcGIS Online credentials when prompted.

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: