Exercise 4: Clean up and complete a Xamarin.iOS binding project (IOS451)

The primary goal of this lab is to create and clean up the binding definition files created from a static Xcode library using Objective Sharpie and complete a Xamarin.iOS binding project using Visual Studio.

If you haven't already, you will need to download Objective Sharpie. Additionally, you will need to complete this exercise on a Mac running macOS 10.10 or newer for compatiblity with Objective Sharpie.

To complete the exercise, you will need Visual Studio for Windows or macOS with the Xamarin development tools installed. You will also need either an emulator/simulator or a device to run the exercise on. Please see the setup page if you need help installing the Xamarin development environment. For compatibility with Objective Sharpiew, you will need a machine running macOS 10.10 or newer.

Create API definition for WeatherGadget

Using a macOS machine, we will create the binding API definition files using the provided WeatherGadget library in the Exercise 4 > Assets folder of your copy of the cloned or downloaded course materials.

1. Create a folder for you exercise content.

Note: there are versions of Xamarin.iOS that will not handle iOS binding projects correctly when the path contains spaces. If you can avoid spaces in your working path, it might be worth doing so for this exercise.

2. Copy the WeatherGadget asset folder to your new exercise folder.
3. Use Objective Sharpie to manually bind the WeatherGadget header files.

Show me how to create the API definition

sharpie bind -output WeatherGadgetOut -namespace WeatherGadgetSDK \
-sdk iphoneos11.4 -scope WeatherGadget.framework/Headers \
WeatherGadget.framework/Headers/WeatherGadget.h

Create Xamarin.iOS bindings library

Next, we will create a bindings library to contain our generated API definition.

With our binding API definition, you could now take the resulting files and the original WeatherGadget library from the Exercise 4 > Assets to Visual Studio on Windows or macOS for the remainder of this exercise.

You will still require a macOS build host when using Visual Studio on Windows.

3. Name the project "WeatherGadgetSDK".

Import WeatherGadget API definition

1. Replace the contents of the binding library's ApiDefinition.cs template-generated file with the contents of the Objective Sharpie-generated ApiDefinitions.cs file.
2. Check and clean up any [Verify] attributes, if any were generated.

4. Navigate to the Exercise 4 > Assets folder and select the WeatherGadget.framework folder as a native reference.

What is happening here?

5. Build the library to make sure it compiles successfully.

Create Xamarin.iOS application to test the binding

Now, we will create a Xamarin.iOS application that we can use to consume and test out our binding.

Verify the WeatherGadgetSDK binding in your iOS app

Now, we can test the bindings library is working correctly in the new iOS app.

1. In your app view controller's ViewDidLoad method, create an instance of the Weather type.
2. Set the CurrentTemperature property to 99f.
3. Call Debug.WriteLine with your instance variable's CurrentTemperature property to see if the value was set properly.

public override void ViewDidLoad() {
    base.ViewDidLoad();

    Weather myWeather = new Weather();
    myWeather.CurrentTemperature = 99f;
    Debug.WriteLine($"Temperature: {myWeather.CurrentTemperature}");
}

We can also test out the WeatherGadgetDelegate class.

1. Create a new GadgetDelegate class in the iOS app which inherits from the WeatherGadgetDelegate class.
2. Implement the required delegate member DidFetchWeather. When implementing the member, make sure to check the NSError parameter is null.
3. Call Debug.WriteLine to report the value of the returned CurrentTemperature.

using System.Diagnostics;
using Foundation;
using WeatherSDK;

namespace WeatherGadgetApp {
    public class GadgetDelegate : WeatherGadgetDelegate{
        public override void DidFetchWeather(Weather weather, NSError withError) {
            if (withError == null) {
                Debug.WriteLine($"Delegate Answering: {weather.CurrentTemperature}");
            }
        }
    }
}

To test the delegate, we need to create a new GadgetDelegate for the WeatherGadget we created earlier.

1. Back in your app view controller's ViewDidLoad method, create an instance of GadgetDelegate.
2. Set the Delegate property to the new GadgetDelegate instance.
3. Invoke the FetchWeather method on the WeatherGadget instance to test the delegate implementation.

public override void ViewDidLoad() {
    base.ViewDidLoad();

    ...

    WeatherGadget wGadget = new WeatherGadget();
    wGadget.Delegate = new GadgetDelegate();
    wGadget.FetchWeather();
}

4. Run the application to make sure the expected Debug statements are logged.

If you followed along with the provided code, you should see the following output:

[0:] Temperature: 99
[0:] Delegate Answering: -20

Note: If your iOS app isn't building due to missing namespaces and classes from the API definition, you may be running a version of Xamarin.iOS that will not handle iOS binding projects correctly when the path contains spaces. Try moving your exercise code to a path without spaces and try again.

Exercise summary

In this exercise you created and cleaned up the binding definition files for a static Xcode library using Objective Sharpie. You then used the API definition files in a Xamarin.iOS binding project and tested this new bindings library in a Xamarin.iOS project.

You can view the completed solution in the Exercise 4 > Completed folder of your copy of the cloned or downloaded course materials.