App Startup — Under the hood with Koin library Example

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App Startup is a part of the library of Android Jetpack. This provides a way to initialize the components needed to start the application. In this article, let’s take the Koin library as an example to learn how the App Startup library works and what benefits it has.

Why do you use it? 🧐

We usually use the content providers to initialize the required components when the app starts. However, the content providers is expensive and initialized in an undetermined order. use App Startup, you can initialize the components you need to start the app, define the initialization order explicitly, and provide good performance.

How do I use it? 👀

To use this, we need to override two methods. Let’s take a Koin library as an example.

The Initializer interface defines two methods.

create() : Returns the instance, including the operation required to initialize the component.
dependencies() : You can control the order of execution by returning a different list of initializers. For example, if you want to run the another initializer after KoinInitializer first, then you can use it as follows!

// another initializer classoverride fun dependencies(): MutableList<Class<out Initializer<*>>>{    // initialized after Koin in initialized
    return mutableListOf(KoinInitializer::class.java)
}

Now, all you have to do is add a content provider to your AndroidManifestfile.

If you want to disable single or all automatic initialization or manually initialize components, please review the official document.✨

https://developer.android.com/topic/libraries/app-startup

Under the Hood

Let’s take a look at the InitializationProvider class that we wrote first.

This class inherits ContentProvider and calls the discoverAndInitialize()method of AppInitializer if the context is not null in the onCreate()method. So what is AppInitializer?

AppInitializer class

We can see that AppInitializer is basically implemented as a Singleton Pattern. Let’s move on to the discoverAndInitialize() method.

AppInitializer class

The code is a little long, but let’s just look at the important part. First, I’m getting the ComponentName from on line 4 and then the ProviderInfo. And on line 11, if metadata is not null, all keys are imported, and if it is valid information, we saved it in mDiscovered and executed the doInitialize()method.

Then let’s look at the doInitialize() method.

After checking to see if the component is already initialized on line 10, check to see if it exists in mInitialized on line 18. If it does not exist, take the dependencies list from the component initializer parameters on line 23 and call doInitialize() again if it’s not empty. Then invoke the create()method to initiate the initialization operation.

Conclusion

If you have many components that need to be initialized when you start an application, try using App StartUp. I think I can trust and use it because the official version is out.