Easy way to get current Activity, Fragment, LifeCycleOwner from within View?

Question

When writing Views, ViewModels and LiveData are lifecycle aware. The ViewModel want's the current FragmentActivity, LiveData the current LifecycleOwner. You don't know in advance if your View will be wrapped or somewhat. So it requires a flexible function to to find the wanted context. I ended up with this two methods:

private FragmentActivity getFragmentActivity() {
    Context context = getContext();
    while (!(context instanceof FragmentActivity)) {
        context = ((ContextWrapper) context).getBaseContext();
    }
    return (FragmentActivity) context;
}

private LifecycleOwner getLifecycleOwner() {
    Context context = getContext();
    while (!(context instanceof LifecycleOwner)) {
        context = ((ContextWrapper) context).getBaseContext();
    }
    return (LifecycleOwner) context;
}

Now this is a lot of boilerplate code to put into each View. Is there a more easy way?

I don't want to use a customised View base class for this, as large hierarchy's are ugly. Composition on the other hand requires as much code as this solution.

use getActivity().getApplicationContext() to get current activity, fragment. — Dinith Rukshan Kumara, Mar 02 '18 at 19:27
@Santanu Sur: The application context is always the same. There is no lifecycle awareness in it. — Blcknx, Mar 02 '18 at 19:29
@CommonsWare: Depends on your architecture. Currently I plug the real model into the view and treat the view model as internal implementation. Hence, for me the `View` is the place to create the view model, so I need the lifecycle. The advantage of this approach is, that I can always use the same Interface to plug model and view independent of the usage of a view model or none. -- However, this difficulties, to get the actual lifecycle is a reason to review my pattern of architecture. — Blcknx, Mar 02 '18 at 19:36
@ DINITH RUKSHAN KUMARA: There is no getActivity() in the View. — Blcknx, Mar 02 '18 at 19:47

score 20 · Accepted Answer · answered May 18 '21 at 05:16

20

you can find it lifecycle-runtime-ktx :

fun View.findViewTreeLifecycleOwner(): LifecycleOwner? = ViewTreeLifecycleOwner.get(this)

answered May 18 '21 at 05:16

Ahmadreza Moodi

463
4
10

Abhinav Atul · Answer 2 · 2020-07-08T04:57:23.213

Kotlin Extensions

fun Context.fragmentActivity(): FragmentActivity? {
    var curContext = this
    var maxDepth = 20
    while (--maxDepth > 0 && curContext !is FragmentActivity) {
        curContext = (curContext as ContextWrapper).baseContext
    }
    return if(curContext is FragmentActivity)
        curContext
    else
        null
}

fun Context.lifecycleOwner(): LifecycleOwner? {
    var curContext = this
    var maxDepth = 20
    while (maxDepth-- > 0 && curContext !is LifecycleOwner) {
        curContext = (curContext as ContextWrapper).baseContext
    }
    return if (curContext is LifecycleOwner) {
        curContext as LifecycleOwner
    } else {
        null
    }
}

Usage

val lifecycleOwner = context.lifecycleOwner()
val fragmentActivity = context.fragmentActivity()

What is the maxDepth = 20? Is that just an arbitrary number to reduce a large loop. Any reason why you would have a loop with this many iterations? — Stimsoni, Nov 17 '20 at 00:01

score 1 · Answer 3 · answered Dec 09 '20 at 15:22

1

Similar to another answer, but without needing to specify maxDepth:

 val Context.lifecycleOwner: LifecycleOwner?
    get() {
        var context: Context? = this

        while (context != null && context !is LifecycleOwner) {
            val baseContext = (context as? ContextWrapper?)?.baseContext
            context = if (baseContext == context) null else baseContext
        }

        return if (context is LifecycleOwner) context else null
    }

answered Dec 09 '20 at 15:22

jc12

1,411
1
18
24

2

If view in fragment, this method will get activity's LifecycleOwner. It may cause fragment memory leak. – xymelon Jan 07 '21 at 09:01

score 0 · Answer 4 · answered Jun 06 '19 at 15:30

If you don't want to use composition you can put this into common BaseView class. Alternatively, you can make it a static method in some utils class.

If you use Kotlin you can also make it Kotlin extension function, what is my most favourite way of doing that.

Easy way to get current Activity, Fragment, LifeCycleOwner from within View?

4 Answers4