Extending the Application Class & Good Practices

Question

I have been told recently that extending the Application Class in order to use it as a Singleton was a bad practice but without any explanation.
So what are the potentials problem behind the use of this class ? I have seen it used in many projects.

Also, if using the Application Class is a bad idea, what are the alternatives to store application level variables ?

Answer 1

Using a Singleton approach is not really a bad idea, but it may be troublesome in the cases when being used in a multi-threaded environment where one thread sets a value to a variable and the other thread may over-write that value without any notice.

However, in order to keep application level instances/variables, it is suggested to extend Application class and define it in your AndroidManifest.xml as the default one. Since the application's context is created only once (till the application is running and stays in the memory) when you launch that application, so you may define some variables inside that class to make them availabe anywhere in your application's code using public methods.

Moreover, you may use your application class as Singleton too, since its guaranteed to be created only once when launched.