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// https://github.com/Zhuinden/fragmentviewbindingdelegate-kt | |
import android.view.View | |
import androidx.fragment.app.Fragment | |
import androidx.lifecycle.DefaultLifecycleObserver | |
import androidx.lifecycle.Lifecycle | |
import androidx.lifecycle.LifecycleOwner | |
import androidx.lifecycle.Observer | |
import androidx.viewbinding.ViewBinding | |
import kotlin.properties.ReadOnlyProperty | |
import kotlin.reflect.KProperty | |
class FragmentViewBindingDelegate<T : ViewBinding>( | |
val fragment: Fragment, | |
val viewBindingFactory: (View) -> T | |
) : ReadOnlyProperty<Fragment, T> { | |
private var binding: T? = null | |
init { | |
fragment.lifecycle.addObserver(object : DefaultLifecycleObserver { | |
val viewLifecycleOwnerLiveDataObserver = | |
Observer<LifecycleOwner?> { | |
val viewLifecycleOwner = it ?: return@Observer | |
viewLifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver { | |
override fun onDestroy(owner: LifecycleOwner) { | |
binding = null | |
} | |
}) | |
} | |
override fun onCreate(owner: LifecycleOwner) { | |
fragment.viewLifecycleOwnerLiveData.observeForever(viewLifecycleOwnerLiveDataObserver) | |
} | |
override fun onDestroy(owner: LifecycleOwner) { | |
fragment.viewLifecycleOwnerLiveData.removeObserver(viewLifecycleOwnerLiveDataObserver) | |
} | |
}) | |
} | |
override fun getValue(thisRef: Fragment, property: KProperty<*>): T { | |
val binding = binding | |
if (binding != null) { | |
return binding | |
} | |
val lifecycle = fragment.viewLifecycleOwner.lifecycle | |
if (!lifecycle.currentState.isAtLeast(Lifecycle.State.INITIALIZED)) { | |
throw IllegalStateException("Should not attempt to get bindings when Fragment views are destroyed.") | |
} | |
return viewBindingFactory(thisRef.requireView()).also { this.binding = it } | |
} | |
} | |
fun <T : ViewBinding> Fragment.viewBinding(viewBindingFactory: (View) -> T) = | |
FragmentViewBindingDelegate(this, viewBindingFactory) |
@Drjacky I see that you forgot to add the layout name in the class FragBlah : Fragment() . It should be class FragBlah : Fragment(R.layout.your_layout_name).
@flamesoft But we have setContentView(binding.root)
in onCreate
for Activity and = binding.root
in onCreateView
I haven't tried this. I have just tested it with fragments and that works. Try to use fragment and see if it works. @Drjacky
How would I use this in DialogFragment?
I just don't use this in a DialogFragment.
@Zhuinden Isn't it possible to add support for it, or have a similar solution for it?
@AndroidDeveloperLB There are two "flavors" of DialogFragment
, they have different view lifecycle. You can find examples for both cases here.
@gmk57 Oh these make sense. Thank you!
sounds like you are missing
val binding = binding
in youronViewCreated
OR you are actually accessing the view afteronDestroyView
and potentially have a memory leak in your app anyway.
Btw there is an updated version of this gist as a library in https://github.com/Zhuinden/fragmentviewbindingdelegate-kt
@Zhuinden what is the real reason behind val binding = binding
in most cases we directly access binding. is this required ? .
@manju23reddy I debugged a guy's code who had trouble with callbacks of a WebView running on a different thread and this was the fix, so I do do it in my code personally.
I've had to do a modification on this idea that allows us to use the binding right before it gets nullified.
An example scenario is when we need to null the adapter of a recyclerView when a fragment is destroyed. Using this gist will lead to a crash because the life cycle state DESTROYED
is set before any of the onDestroy*
methods are called inside the fragment, which causes the throw
in line 50 of this gist.
I've added an optional onDestroyListener
parameter to the class, ex:
class FragmentViewBindingDelegate<T : ViewBinding>(
val fragment: Fragment,
val viewBindingFactory: (View) -> T,
val onDestroyListener: () -> Unit = {}
) : ReadOnlyProperty<Fragment, T> {
Which is then used inside the observer's onDestroy
, ex:
viewLifecycleOwner.lifecycle.addObserver(object : DefaultLifecycleObserver {
override fun onDestroy(owner: LifecycleOwner) {
onDestroyListener()
binding = null
}
})
This guarantees that any sync code inside that listener has access to the binding before it is null, which allows me to, for example, remove the adapter of a recyclerView when the fragment is destroyed.
@ParticleCore i did eventually move this code to a library in https://github.com/Zhuinden/fragmentviewbindingdelegate-kt because these oddities kept coming up inherited from Google's code so it made sense to version it instead.
In that case, the problem is that you have some listener that is called even after onDestroyView.
That's not a bug in this code.