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 should:
Have an ArcGIS account and an API key to access ArcGIS services. If you don't have an account, sign up for free.
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.
Steps
Open the Visual Studio solution
To start the tutorial, complete the Display a map tutorial or download and unzip the solution.
Open the .sln file in Visual Studio.
If you downloaded the solution project, set your API key.
An API Key enables access to services, web maps, and web scenes hosted in ArcGIS Online.
If necessary, set the API Key.
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 Visual Studio, in the Solution Explorer, click App.xaml.cs.
In the App class, add an override for the OnStartup() function to set the ApiKey property on ArcGISRuntimeEnvironment.
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publicpartialclassApp : Application {
protectedoverridevoidOnStartup(StartupEventArgs e) {
base.OnStartup(e);
// Note: it is not best practice to store API keys in source code.// The API key is referenced here for the convenience of this tutorial. Esri.ArcGISRuntime.ArcGISRuntimeEnvironment.ApiKey = "YOUR_API_KEY";
}
}
}
If you are developing with Visual Studio for Windows, ArcGIS Maps SDK for .NET provides a set of project templates for each supported .NET platform. These templates provide all of the code needed for a basic Model-View-ViewModel (MVVM) app. Install the ArcGIS Maps SDK for .NET Visual Studio Extension to add the templates to Visual Studio (Windows only). See Install and set up for details.
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.
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.
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.
"[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.