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Showing content from https://developers.arcgis.com/kotlin/layers/tutorials/add-a-feature-layer-from-a-portal-item/ below:

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

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 the following:

An ArcGIS Location Platform or ArcGIS Online account.
A development and deployment environment that meets the system requirements.
An IDE for Android development in Kotlin.

Note

It is recommended that you use the latest stable version Android Studio to create this tutorial app. The code described in the steps below, however, should work in any up-to-date Android IDE that supports Kotlin.

Develop or download

You have two options for completing this tutorial:

Option 1: Develop the code Open an Android Studio project with Gradle

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.
Modify the old project for use in this new tutorial.
1. On your file system, delete the .idea folder, if present, at the top level of your project.
2. In the Android view, open app > res > values > strings.xml.
  
  In the <string name="app_name"> element, change the text content to Add a feature layer from a portal item.
  
  strings.xml
  
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```
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<resources>
    <string name="app_name">Add a feature layer from a portal item</string>
</resources>
```
3. In the Android view, open Gradle Scripts > settings.gradle.kts.
  
  Change the value of rootProject.name to "Add a feature layer from a portal item".
  
  settings.gradle.kts
  
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```
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dependencyResolutionManagement {
    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
    repositories {
        google()
        mavenCentral()
        maven { url = uri("https://esri.jfrog.io/artifactory/arcgis") }
    }
}

rootProject.name = "Add a feature layer from a portal item"
include(":app")
```
4. Click File > Sync Project with Gradle files. Android Studio will recognize your changes and create a new .idea folder.

Add import statements

In the Android view, open app > kotlin+java > com.example.app > MainScreen.kt. Replace the import statements with the imports needed for this tutorial.

MainScreen.kt

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@file:OptIn(ExperimentalMaterial3Api::class)

package com.example.app.screens

import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.material3.ExperimentalMaterial3Api
import androidx.compose.material3.Scaffold
import androidx.compose.material3.Text
import androidx.compose.material3.TopAppBar
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.res.stringResource
import com.arcgismaps.mapping.ArcGISMap
import com.arcgismaps.mapping.BasemapStyle
import com.arcgismaps.mapping.PortalItem
import com.arcgismaps.mapping.Viewpoint
import com.arcgismaps.mapping.layers.FeatureLayer
import com.arcgismaps.portal.Portal
import com.arcgismaps.toolkit.geoviewcompose.MapView
import com.example.app.R

Add a feature layer to the map

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: 2e4b3df6ba4b44969a3bc9827de746b3. You will then add that feature layer to your map's collection of data layers (operational layers).

In MainScreen, before the code that creates the ArcGISMap, create a new Portal referencing ArcGIS Online as the url parameter and Portal.Connection.Anonymous for the connection parameter.

MainScreen.kt

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fun createMap(): ArcGISMap {

    val portal = Portal(
        url = "https://www.arcgis.com",
        connection = Portal.Connection.Anonymous
    )

    return ArcGISMap(BasemapStyle.ArcGISTopographic).apply{
        initialViewpoint = Viewpoint(
            latitude = 34.0270,
            longitude = -118.8050,
            scale = 72000.0
        )

    }

}

Then, create a PortalItem instance, passing portal and the id of the portal item that the feature layer will use.

MainScreen.kt

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fun createMap(): ArcGISMap {

    val portal = Portal(
        url = "https://www.arcgis.com",
        connection = Portal.Connection.Anonymous
    )

    val portalItem = PortalItem(
        portal = portal,
        itemId = "2e4b3df6ba4b44969a3bc9827de746b3"
    )

    return ArcGISMap(BasemapStyle.ArcGISTopographic).apply{
        initialViewpoint = Viewpoint(
            latitude = 34.0270,
            longitude = -118.8050,
            scale = 72000.0
        )

    }

}

Next, create a FeatureLayer using FeatureLayer.createWithItem(), to which you pass the portal item.

MainScreen.kt

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fun createMap(): ArcGISMap {

    val portal = Portal(
        url = "https://www.arcgis.com",
        connection = Portal.Connection.Anonymous
    )

    val portalItem = PortalItem(
        portal = portal,
        itemId = "2e4b3df6ba4b44969a3bc9827de746b3"
    )

    val featureLayer = FeatureLayer.createWithItem(portalItem)

    return ArcGISMap(BasemapStyle.ArcGISTopographic).apply{
        initialViewpoint = Viewpoint(
            latitude = 34.0270,
            longitude = -118.8050,
            scale = 72000.0
        )

    }

}

In the apply block for ArcGISMap, add the feature layer to the map.

MainScreen.kt

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fun createMap(): ArcGISMap {

    val portal = Portal(
        url = "https://www.arcgis.com",
        connection = Portal.Connection.Anonymous
    )

    val portalItem = PortalItem(
        portal = portal,
        itemId = "2e4b3df6ba4b44969a3bc9827de746b3"
    )

    val featureLayer = FeatureLayer.createWithItem(portalItem)

    return ArcGISMap(BasemapStyle.ArcGISTopographic).apply{
        initialViewpoint = Viewpoint(
            latitude = 34.0270,
            longitude = -118.8050,
            scale = 72000.0
        )

        operationalLayers.add(featureLayer)

    }

}

Click Run > Run > app to run the app.

You should see a map of trail heads in the Santa Monica mountains. Double tap, Drag, pinch in, and pinch out 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 side of this page.
Unzip the file to a location on your machine.
Run Android Studio.
Go to File > Open.... Navigate to the solution folder and click Open.

On Windows: If you are in the Welcome to Android Studio dialog, click Open and navigate to the solution folder. Then click Open.

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.

Security and authentication guide

To 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):
- 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 the Android view of Android Studio, open app > kotlin+java > com.example.app > MainActivity. Set the AuthenticationMode to .API_KEY.

MainActivity.kt

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class MainActivity : ComponentActivity() {

    private enum class AuthenticationMode { API_KEY, USER_AUTH }

    private val authenticationMode = AuthenticationMode.API_KEY

Set the apiKey property with your API key access token.

MainActivity.kt

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    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        when (authenticationMode) {
            AuthenticationMode.API_KEY -> {

                ArcGISEnvironment.apiKey = ApiKey.create("YOUR_ACCESS_TOKEN")

            }

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.

In the Android view of Android Studio, open app > kotlin+java > com.example.app > MainActivity. Set the AuthenticationMode to .USER_AUTH.

MainActivity.kt

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class MainActivity : ComponentActivity() {
    private enum class AuthenticationMode { API_KEY, USER_AUTH }

    private val authenticationMode = AuthenticationMode.USER_AUTH

Set your clientID and redirectURL values. You must use the RedirectURL that you supplied for your app in the user authentication part of the Set up authentication step.

MainActivity.kt

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            AuthenticationMode.USER_AUTH -> {
                authenticatorState.oAuthUserConfigurations = listOf(
                    OAuthUserConfiguration(
                        portalUrl = "https://www.arcgis.com",

                        clientId = "YOUR_CLIENT_ID",
                        redirectUrl = "YOUR_REDIRECT_URL"

                    )
                )

Open app > manifests > AndroidManifest.xml.

Set the android:scheme and android:host using the scheme and host from your RedirectURL.

A redirectURL is composed of a scheme and a host component. The format for the redirect url is scheme://host. For example, if the redirect url is myscheme://myhost then the scheme is myscheme and the host is myhost.

AndroidManifest.xml

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                <data
                    android:scheme="your_redirect_url_scheme"
                    android:host="your_redirect_url_host" />

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 app

Click Run > Run > app to run the app.

You should see a map of trail heads in the Santa Monica mountains. Double tap, Drag, pinch in, and pinch out 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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