ViewBinding delegates

Author: Lucas Sales

app/src/main/java/com/monstarlab/extensions/ActivityViewBindingDelegate.kt

@@ -0,0 +1,44 @@
+package com.monstarlab.extensions
+
+import android.view.LayoutInflater
+import androidx.appcompat.app.AppCompatActivity
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleObserver
+import androidx.lifecycle.OnLifecycleEvent
+import androidx.viewbinding.ViewBinding
+import kotlin.properties.ReadOnlyProperty
+import kotlin.reflect.KProperty
+
+class ActivityViewBindingDelegate<T : ViewBinding>(
+    private val activity: AppCompatActivity,
+    private val viewBinder: (LayoutInflater) -> T,
+    private val beforeSetContent: () -> Unit = {}
+) : ReadOnlyProperty<AppCompatActivity, T>, LifecycleObserver {
+
+    private var activityBinding: T? = null
+
+    init {
+        activity.lifecycle.addObserver(this)
+    }
+
+    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
+    fun createBinding() {
+        initialize()
+        beforeSetContent()
+        activity.setContentView(activityBinding?.root)
+        activity.lifecycle.removeObserver(this)
+    }
+
+    private fun initialize() {
+        if (activityBinding == null) {
+            activityBinding = viewBinder(activity.layoutInflater)
+        }
+    }
+
+    override fun getValue(thisRef: AppCompatActivity, property: KProperty<*>): T {
+        ensureMainThread()
+
+        initialize()
+        return activityBinding!!
+    }
+}

app/src/main/java/com/monstarlab/extensions/FragmentViewBindingDelegate.kt

@@ -0,0 +1,57 @@
+package com.monstarlab.extensions
+
+import android.view.View
+import androidx.fragment.app.Fragment
+import androidx.lifecycle.*
+import androidx.viewbinding.ViewBinding
+import kotlin.properties.ReadOnlyProperty
+import kotlin.reflect.KProperty
+
+class FragmentViewBindingDelegate<T : ViewBinding>(
+    private val fragment: Fragment,
+    private val viewBinder: (View) -> T,
+    private val disposeEvents: T.() -> Unit = {}
+) : ReadOnlyProperty<Fragment, T>, LifecycleObserver {
+
+    private inline fun Fragment.observeLifecycleOwnerThroughLifecycleCreation(crossinline viewOwner: LifecycleOwner.() -> Unit) {
+        lifecycle.addObserver(object : DefaultLifecycleObserver {
+            override fun onCreate(owner: LifecycleOwner) {
+                viewLifecycleOwnerLiveData.observe(
+                    this@observeLifecycleOwnerThroughLifecycleCreation,
+                    Observer { viewLifecycleOwner ->
+                        viewLifecycleOwner.viewOwner()
+                    })
+            }
+        })
+    }
+
+    private var fragmentBinding: T? = null
+
+    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
+    fun disposeBinding() {
+        fragmentBinding?.disposeEvents()
+        fragmentBinding = null
+    }
+
+    init {
+        fragment.observeLifecycleOwnerThroughLifecycleCreation {
+            lifecycle.addObserver(this@FragmentViewBindingDelegate)
+        }
+    }
+
+    override fun getValue(thisRef: Fragment, property: KProperty<*>): T {
+
+        ensureMainThread()
+
+        val binding = fragmentBinding
+        if (binding != null) {
+            return binding
+        }
+
+        val lifecycle = fragment.viewLifecycleOwner.lifecycle
+        if (!lifecycle.currentState.isAtLeast(Lifecycle.State.INITIALIZED)) {
+            throw IllegalStateException("Fragment views are destroyed.")
+        }
+        return viewBinder(thisRef.requireView()).also { fragmentBinding = it }
+    }
+}

app/src/main/java/com/monstarlab/extensions/GlobalViewBindingDelegate.kt

@@ -0,0 +1,14 @@
+package com.monstarlab.extensions
+
+import android.view.View
+import androidx.viewbinding.ViewBinding
+import kotlin.properties.ReadOnlyProperty
+import kotlin.reflect.KProperty
+
+class GlobalViewBindingDelegate<T : ViewBinding>(val viewBinder: (View) -> T) :
+    ReadOnlyProperty<View, T> {
+
+    override fun getValue(thisRef: View, property: KProperty<*>): T {
+        return viewBinder(thisRef)
+    }
+}

app/src/main/java/com/monstarlab/extensions/ViewBindingExtensions.kt

@@ -0,0 +1,35 @@
+package com.monstarlab.extensions
+
+import android.app.Activity
+import android.os.Looper
+import android.view.LayoutInflater
+import android.view.View
+import androidx.appcompat.app.AppCompatActivity
+import androidx.fragment.app.Fragment
+import androidx.viewbinding.ViewBinding
+
+inline fun <T : ViewBinding> Activity.viewBinder(crossinline bindingInflater: (LayoutInflater) -> T) =
+    lazy(LazyThreadSafetyMode.NONE) {
+        bindingInflater.invoke(layoutInflater)
+    }
+
+fun <T : ViewBinding> AppCompatActivity.viewBinding(
+    bindingInflater: (LayoutInflater) -> T,
+    beforeSetContent: () -> Unit = {}
+) =
+    ActivityViewBindingDelegate(this, bindingInflater, beforeSetContent)
+
+fun <T : ViewBinding> Fragment.viewBinding(
+    viewBindingFactory: (View) -> T,
+    disposeEvents: T.() -> Unit = {}
+) =
+    FragmentViewBindingDelegate(this, viewBindingFactory, disposeEvents)
+
+fun <T : ViewBinding> globalViewBinding(viewBindingFactory: (View) -> T) =
+    GlobalViewBindingDelegate(viewBindingFactory)
+
+internal fun ensureMainThread() {
+    if (Looper.myLooper() != Looper.getMainLooper()) {
+        throw IllegalThreadStateException("View can be accessed only on the main thread.")
+    }
+}

app/src/main/java/com/monstarlab/features/sample/SampleFragment.kt

@@ -1,36 +1,18 @@
 package com.monstarlab.features.sample
 
 import android.os.Bundle
-import android.view.LayoutInflater
 import android.view.View
-import android.view.ViewGroup
-import androidx.fragment.app.Fragment
 import com.monstarlab.R
 import com.monstarlab.base.BaseFragment
 import com.monstarlab.databinding.FragmentSampleBinding
 import com.monstarlab.extensions.collectFlow
+import com.monstarlab.extensions.viewBinding
 
-class SampleFragment: BaseFragment(R.layout.fragment_sample) {
+class SampleFragment : BaseFragment(R.layout.fragment_sample) {
 
-    val viewModel by viewModel<SampleViewModel>()
+    private val viewModel by viewModel<SampleViewModel>()
 
-    private var _binding: FragmentSampleBinding? = null
-    private val binding get() = _binding!!
-
-    override fun onCreateView(
-        inflater: LayoutInflater,
-        container: ViewGroup?,
-        savedInstanceState: Bundle?
-    ): View? {
-        _binding = FragmentSampleBinding.inflate(inflater, container, false)
-        val view = binding.root
-        return view
-    }
-
-    override fun onDestroyView() {
-        super.onDestroyView()
-        _binding = null
-    }
+    private val binding by viewBinding(FragmentSampleBinding::bind)
 
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)