Using WeakReference in MvpBasePresenter is flawed

Hi,

Using WeakReference inside MvpBasePresenter may potentially lead to NullPointerException in the code like this (taken from the sample code on your site):

if (isViewAttached())
          getView().showHello(greetingText);

There is no guarantee that GarbageCollector will not remove object from memory between two subsequent calls to WeakReference.get(). This way even when isViewAttached() returns true, getView() may return null. The correct and only way to use WeakReference in this case would be to call WeakReference.get() only once and assign the result to strong reference.

[sockeqwe]

Thanks for reporting! Indeed, that is true, unlikely but in theory this could happen! Actually I wanted to deprecate isViewAttached() in 3.0.

The proper way is:

V view = getView();
if (view !=null){
    view.showHello(...);
}

We could add a shorthand like this to MvpBasePresenter:

ifViewAttached(view -> view.showHello(...));

which internally uses View view = getView(); if (view != null) { ... } as shown in the first code snippet.

What do you think?

[sockeqwe]

yes but still this could happen (theoretically):

view?.toThis()  // this is executed
// gc runs and view == null
view?.toThat() // this is not executed because view == null because of gc

whereas with ifViewAttached() its a do all in the lambda because view is guaranteed not to be null or don’t execute the lambda at all. Also we have to take java users into account.

Also this API seems to me more consistent to what MvpQueuingBasePresenter offers:

onceViewAttached { view -> 
   view.doThis()
   view.doThat()
}