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.
PrerequisitesBefore 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 downloadYou have two options for completing this tutorial:
Option 1: Develop the codeTo 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 solutionThe 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.
Rename the namespace used by classes in the project.
MapViewModel class, double-click the namespace name (DisplayAMap) to select it, and then right-click and choose Rename....Build the project.
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
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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;
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.
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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();
}
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
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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;
// 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
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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;
// 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);
}
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 solutionClick 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 authenticationTo 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
Learn more in API key authentication.
User authentication
Learn more in User authentication.
Security and authentication guideTo learn more about the different types of authentication, visit Types of 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):
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.
WarningConfiguration steps later in the tutorial will assume that your redirect URL is my-app://auth. If you use a different URL, make sure to configure your app's settings accordingly.
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 solutionTo 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
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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
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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
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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 solutionClick 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:
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