Xamarin and Chartboost

Xamarin and Chartboost SDK iOS Bindings

When developing a cross platform app (PCL) using Xamarin I needed to integrate with the Chartboost SDK. I spent a lot of time searching and could not find any bindings projects and most of the references on the usual forums where years out of date.

So I took the plunge and decided to have a go at building it myself, I read the official documents from Xamarin and they are helpful but still felt a bit out of date and also never had a walkthrough of using an iOS .framework SDK.

The first step which all article agree on was to download Sharpie from https://developer.xamarin.com/guides/cross-platform/macios/binding/objective-sharpie/ this utility from Xamarin helps create the C# bindings for the library file.
Fire up Xamarin and Create a New Solution and choose to create an iOS Library > Bindings Library
Download the latest SDK from Chartboost (at the time of writing mine is v6.6.3)
Expand the Chartboost .zip and navigate to Chartboost-iOS-6.6.3/Chartboost.framework/Versions/Current folder
In that folder there is a file called Chartboost (its around 50Mb)
You need to rename this file to Chartboost.a (this is a key step I never saw mentioned in the docs)
Drag the Chartboost.a file onto your Xamarin project and it will create a Chartboost.linkwith.cs file and show it under the Chartboost.a
Now you are ready to run Sharpie, so open a Terminal and change the current directory to the Xamarin project folder
Run this command to find out what the latest SDK version you have is sharpie xcode –sdks and look for a line like sdk: iphoneos10.3 arch: arm64 armv7 you will need the sdk name on the next command
The command I used was as follows, notice the long path, I am telling Sharpie where the chartboost.framework file is relative to the Xamarin project folder sharpie bind -framework ../../../Chartboost-iOS-6.6.3/Chartboost.framework -sdk iphoneos10.3 -namespace Chartboost
You will now have a completed ApiDefinition.cs and Structs.cs file with the Chartboost API. Sometimes I found Sharpie aded an extra but similar named files, if this happens, open up the new files and copy over to the ApiDefinition.cs and Structs.cs files
Open the Structs.cs file and replace the nuint with ulong as the type
There a number of Verify compiler directives, which I just removed from both the ApiDefinition.cs and Structs.cs files

You now have a valid project that you can compile and make a binding library file for use in other Xamarin projects. The next step is how to get the Chartboost library working in a PCL project.

There are 3 steps, first you need to define a delegate to pass into the Chartboost library which can respond to the events being raised. The key thing I found here was to not call the CacheInterstitial until the DidInitialize event fires. I lost some time figuring this out as in a native iOS app I’ve never had to do that:

public class CBDel : ChartboostDelegate
{
    public override void DidCacheInterstitial(string location)
    {
        Debug.WriteLine("DidCacheInterstitial:" + location);
    }

    public override void DidFailToLoadInterstitial(string location, CBLoadError error)
    {
        Debug.WriteLine("DidFailToLoadInterstitial" + error.ToString());
    }

    public override void DidInitialize(bool status)
    {
        Debug.WriteLine("DidInitialize" + status.ToString());
        Chartboost.SetShouldPrefetchVideoContent(true);
        Chartboost.CacheInterstitial( Constants.CBLocationHomeScreen);
    }
}

Now you need to initialise the Chartboost library, so define an instance of your delegate to pass into the initialise:

public static CBDel del = new CBDel();

public override bool FinishedLaunching(UIApplication application, NSDictionary launchOptions)
{
    Chartboost.StartWithAppId("APPID HERE", "APP SECRET HERE", del);
    Chartboost.SetShouldPrefetchVideoContent(true);

    return true;
}

Finally here is the code in a simple button to show the interstitial:

partial void UIButton3_TouchUpInside(UIButton sender)
{
    bool ret = Chartboost.HasInterstitial( Constants.CBLocationHomeScreen);
    if (ret)
        Chartboost.ShowInterstitial( Constants.CBLocationHomeScreen);
    else
        Chartboost.CacheInterstitial( Constants.CBLocationHomeScreen);
}

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Xamarin and Chartboost SDK iOS Bindings