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
The following are required for this tutorial:
An ArcGIS account to access API keys. If you don't have an account, sign up for free.
A development and deployment environment that meets the system requirements.
An IDE for Android development in Kotlin.
Steps
Open an Android Studio project with Gradle
To start this tutorial, complete the Display a map tutorial. Or download and unzip the Display a map solution in a new folder.
Modify the old project for use in this new tutorial. Expand More info for instructions.
On your file system, delete the .idea folder, if present, at the top level of your project.
In the Android tool window, 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
Use dark colors for code blocks
1
2
3
4
5
Change line
1
2
3
4
5
<resources><stringname="app_name">Add a feature layer from a portal item</string></resources>
In the Android tool window, open Gradle Scripts > settings.gradle.
Change the value of rootProject.name to "Add a feature layer from a portal item".
Click File > Sync Project with Gradle files. Android Studio will recognize your changes and create a new .idea folder.
If you downloaded the Display a map solution project, get your API key and set it in your app.
An API Key enables access to services, web maps, and web scenes hosted in ArcGIS Online.
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.
In Android Studio: in the Android tool window, open app > java > com.example.app > MainActivity.
In the setApiKey() function, find the ApiKey.create() call and paste your API key inside the quotes, replacing YOUR_API_KEY.
MainActivity.kt
Use dark colors for code blocks
Change line
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
privatefunsetApiKey() {
// It is not best practice to store API keys in source code. We have you insert one here// to streamline this tutorial. ArcGISEnvironment.apiKey = ApiKey.create("YOUR_API_KEY")
}
Prepare files before coding the app
Modify the files from the Display a map tutorial so they can be used in this tutorial: you will add imports and remove code that we will not need.
In the Project tool window, make sure that the Android view is displayed. Open app/java/com.example.app, and click MainActivity.kt. Add the following imports, replacing those from the Display a map tutorial.
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 the setupMap() function, add the following: create a PortalItem object referencing the portal item that the feature layer will use. To do this, provide the item ID and an Portal object.
Load the portal item.The PortalItem class implements the Loadable interface, which declares the suspend function load(). As a suspend function, it must be called in a coroutine scope; we create one here with lifecycleScope.launch().
The load() function returns a Result<Unit>, on which you should call .onSuccess and pass a lambda. In the lambda, create a FeatureLayer with the PortalItem and a layer ID of 0.
A layer ID is required because a portal item may have more than one layer. For instance, when a feature service has 3 layers, such as trailheads (points), trails (polylines) and trail areas (polygons), the corresponding portal item would contain all three layers.
When you build and run an app in Android Studio, you must first select a device. From the Android Studio toolbar, you can access the drop-down list of your currently available devices, both virtual and physical.
.
If you cannot access the list on the toolbar, click Tools > Device Manager.
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.