Add a feature layer from a portal item | ArcGIS Maps SDK for Flutter

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.
Your system meets the system requirements.
You need an IDE for Flutter - we recommend VS Code.

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 Flutter project

Open the project you created by completing the Display a map tutorial.
Continue with the following instructions to use an ArcGIS portal item to access and display a feature layer in a map.

Add a feature layer to the map

Open lib\main.dart.

Create a PortalItem referencing the feature layer by passing in the portal and item ID.

Each portal item has a unique ItemID, identified from its URL on ArcGIS Online.

In your browser, go to the Trailheads Styled layer on ArcGIS Online and find the item ID at the end of the URL. It should be 2e4b3df6ba4b44969a3bc9827de746b3.

The feature layer referenced with this portal item contains trailheads in and around the Santa Monica Mountains.

main.dart
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  void onMapViewReady() {

    final map = ArcGISMap.withBasemapStyle(BasemapStyle.arcGISTopographic);

    // Create a portal item passing in a portal and item ID.
    final portalItem = PortalItem.withPortalAndItemId(
      portal: Portal.arcGISOnline(),
      itemId: '2e4b3df6ba4b44969a3bc9827de746b3',
    );

Create a FeatureLayer from the portal item and a layer ID. The layer ID uniquely identifies one of the layers within the portal item. Add the layer to the map's operational layers.

A layer ID is required because a portal item may have more than one layer. For instance, when a feature service has 3 layers - trailheads (points), trails (polylines) and trail areas (polygons), the corresponding portal item would contain all three layers.

main.dart
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    // Create a portal item passing in a portal and item ID.
    final portalItem = PortalItem.withPortalAndItemId(
      portal: Portal.arcGISOnline(),
      itemId: '2e4b3df6ba4b44969a3bc9827de746b3',
    );

    // Create a feature layer from the portal item. The layer ID uniquely identifies
    // the layer within the portal item, as there can be more than one.
    final featureLayer = FeatureLayer.withItem(item: portalItem, layerId: 0);

    // Add the feature layer to the map as an operational layer.
    map.operationalLayers.add(featureLayer);

    // Code from `Display a map` tutorial and remains unchanged.
    _mapViewController.arcGISMap = map;
    _mapViewController.setViewpoint(
      Viewpoint.withLatLongScale(
        latitude: 34.02700,
        longitude: -118.80500,
        scale: 72000,
      ),
    );

Run the app

Make sure you have an Android emulator, iOS simulator or physical device configured and running.
In VS Code, select Run > Run Without Debugging.

You should see a map of trail heads in the Santa Monica mountains. Tap, drag, and zoom 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 under Solution and unzip the file to a location on your machine.
Open the project in VS code.

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

To complete this tutorial, click on the tab in the switcher below for your authentication type of choice, either API key authentication or 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.

Add authentication code and set developer credentials

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

Open lib/main.dart.

In the main() function, set the ArcGISEnvironment.apiKey value to your access token.

main.dart
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void main () {

  ArcGISEnvironment.apiKey = 'YOUR_ACCESS_TOKEN';

  runApp(

    const MaterialApp(home: MainApp())

  );
}

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.

Add the Authenticator toolkit component to manage your OAuth credentials.

Add the ArcGIS Maps SDK for Flutter Toolkit package to your app by following these instructions

Add the following code to main.dart:

Define a final class member inside _MainAppState class, _oAuthUserConfiguration, and initialize it with OAuthUserConfiguration passing in the portalUri, clientId, and redirectUri values.
Add code to revoke all tokens, Authenticator.revokeOAuthTokens(), and clear all credentials, Authenticator.clearCredentials(), from the authenticator's credential store during application sign-out.
Add the Authenticator widget as a parent of the ArcGISMapView widget in the existing widget tree found in the build(). Set the value of the named parameter, oAuthUserConfigurations to a list containing the new member variable _oAuthUserConfiguration.

main.dart
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class _MainAppState extends State<MainApp> {

  final _mapViewController = ArcGISMapView.createController();

  final _oAuthUserConfiguration = OAuthUserConfiguration(
    portalUri: Uri.parse('https://www.arcgis.com'),
    clientId: 'YOUR_CLIENT_ID',
    redirectUri: Uri.parse('YOUR_REDIRECT_URL'),
  );

  @override
  void dispose() {
    Authenticator.revokeOAuthTokens().whenComplete(
      Authenticator.clearCredentials,
    );

    super.dispose();
  }

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      body: Column(
        children: [
          Expanded(
            child: Authenticator(
              oAuthUserConfigurations: [_oAuthUserConfiguration],
              child: ArcGISMapView(
                controllerProvider: () => _mapViewController,
                onMapViewReady: onMapViewReady,
              ),
            ),
          ),
        ],
      ),
    );

  }
}

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.

For Android only, a system browser is required for user authentication. Add the following activity to the Android manifest in your project:

android/app/src/main/AndroidManifest.xml
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        <!-- ... -->

        <activity
            android:name="com.linusu.flutter_web_auth_2.CallbackActivity"
            android:exported="true">
            <intent-filter android:label="flutter_web_auth_2">
                <action android:name="android.intent.action.VIEW" />
                <category android:name="android.intent.category.DEFAULT" />
                <category android:name="android.intent.category.BROWSABLE" />
                <data android:scheme="YOUR_CALLBACK_URL_SCHEME_HERE" />
            </intent-filter>
        </activity>

        <!-- ... -->

Replace YOUR_CALLBACK_URL_SCHEME_HERE with the scheme of the redirect URL used when you set up authentication earlier. This is necessary so that the browser can communicate back to your app after the login workflow completes.

For example, if you have a redirect URL, such as: my-app://auth, the value of the scheme would be: my-app. This value would replace YOUR_CALLBACK_URL_SCHEME_HERE in the activity.

Run the application

Follow these steps to run the application.

In VS Code's terminal, run:
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```
1
flutter pub upgrade
```
Run:
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```
1
dart run arcgis_maps install
```
Make sure you have an Android emulator, iOS simulator or physical device configured and running.
In VS Code, select Run > Run Without Debugging.

You should see a map of trail heads in the Santa Monica mountains. Tap, drag, and zoom on the map view to explore the map.