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Fragment view binding delegate
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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) |
@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.
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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 theonDestroy*
methods are called inside the fragment, which causes thethrow
in line 50 of this gist.I've added an optional
onDestroyListener
parameter to the class, ex:Which is then used inside the observer's
onDestroy
, ex: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.