Why do we have to call super in Android sometimes?

Question

Sometimes when I override methods, I get an exception the first time it's called like below:

05-31 21:32:04.266: E/AndroidRuntime(28471): android.support.v4.app.SuperNotCalledException:  Fragment AnalFragment{41795860 #1 id=0x7f070002} did not call through to super.onDestroy() 

Why are we forced to call super.method()? It makes sense that there are obligations by the parent class, but more importantly, how do we know that a method requires super to be called, rather than waiting for it to crash?

Answer 1

Why are we forced to call super.method()?

The classes that make up the Android SDK can be incredibly complex. For instance, both activities and fragments must perform a number of operations in order to function properly (i.e. managing life cycle, optimizing memory usage, drawing the layout to the screen, etc.). Requiring the client to make a call to the base class (often at the beginning of the method) ensures that these operations are still performed, while still providing a reasonable level of abstraction for the developer.

How do we know that a function method requires super to be called?

The documentation should tell you whether or not this is required. If it doesn't I'd Google-search for some sample code (or check the API demos... or better yet, look at the source code!). It shouldn't be too difficult to figure out.

Answer 2

I know this is not the true intention of the OP, he did ask this question and I don't believe it got a very good answer so, if anybody is ever wondering "Why the heck do I HAVE to call super?!? If they're going to require it, why don't they just do it for me!!!". Here's the answer to that questions....

Basically, super() is something that must be called if you're overriding something that MUST be called, which can often be rather complicated code. Now, the reason they don't just do it for you and call it before your function is mostly so that you have control! :-D

To be more specific, you cannot control IF you call super(), however, you can control WHEN! So, let's say you have some specific code that needs to happen BEFORE super() gets called, you now have the freedom to call super() only after running your code. Or... let's say you require super() to have already ran for your code not to crash, you now have the option to run super() before running your code, hence ensuring that everything is set up for you. Heck, you could even technically override the superclass hardcore and code your own method that takes care of super() itself, and make it so you don't have to call super(), but 99.9% of the time sane people will not need to do this! :-P

So, the short answer to "why do I have to call super()" is... So that you can control when it's called and do things before, or after super() gets ran. :-)