Android best practices for Fragment to Activity co

问题:

I am new to Android Fragment and trying to learn Fragment to Activity communications. What is the better approach(best practice) in Android for Fragment to Activity communication?

Lets say I have FragmentA and ActivityA. After my screen popups FragmentA, I would like to perform somemethod(probably UI related) in ActivityA

Here are two(pattern) possible Solutions:

1. In FragmentA getActivity and cast the Activity to ActivityA and then call somemethod.
2. In FragmentA create an interface callback and then implement that callback in ActivityA. Then on the callback, call somemethod.

Which pattern is more common/perfer in Android development and why. Or do you have an even better way to communicate from fragment to activity in Android to share with me?

Any comments, opinions, and suggestions is highly appreciated and welcome. ^^ .

回答1:

The second solution is the preferred one, because it allows your fragment to be more independent of its hosting activity.

If in the future you decide to put your fragment on a different activity, there are no changes needed on the fragment, and you will only need to implement the interface on your activity.

I'll add a third solution which is using an event bus (Otto for instance), which also works, although some might argue that it makes your code a little less readable.

回答2:

First method will be a bad practice. Second method will work fine but your fragment is going to be tightly coupled with your activity.

There is one more better approach is to use some event bus library like otto Using this you can communicate effectively with loose coupling in your activity & fragment.

回答3:

Your second approach is more flexible. You might not see a huge benefit in one activity and one fragment case. If you have to use the same fragment in another activity, it will most likely break by casting your activity like that. That said, there is nothing wrong with the first approach, but it is just a little restricted.

回答4:

First pattern is best when your fragment is used only by one activity. Second approach is needed if you want your fragment to communicate with some other objects not the activity that hosts fragment. If you always want to communicate with hosting activity callback is not needed. Just create an interface and implement it on as many activities as needed. Then in your fragment cast activity returned by getActivity().

MyInterface myInteface = (MyInterface) getActivity();
myinterface.somemethod();

You can even check if activity implements needed interface(s) etc.

回答5:

The interface approach works fine and is more flexible in so far as it doesn't tie your fragment to the activity directly. One thing you should also consider is how much work the activity might need to do, that is it may end up managing several fragments. This has a tendency to lead to 'fat fragments' as my question here asked when I started using them