refactor: split implementation of mvi fragment with save instance state

to separate the minimal mvi implementation to extended implementation
which handles that state can be restored after killing process by system.

Author: Arkadiusz Pałka

app/build.gradle

@@ -82,4 +82,5 @@ dependencies {
     implementation deps.androidx.material
     implementation deps.androidx.multidex
     implementation deps.androidx.annotation
+    implementation "androidx.lifecycle:lifecycle-common:2.2.0"
 }

app/src/main/java/pl/valueadd/mvi/example/presentation/base/AbstractBackMviFragment.kt

@@ -4,13 +4,26 @@ import android.os.Bundle
 import androidx.annotation.LayoutRes
 import pl.valueadd.mvi.example.utility.dependencyinjection.DependencyUtil
 import pl.valueadd.mvi.fragment.back.BackMviFragment
+import pl.valueadd.mvi.fragment.delegate.fragment.MviFragmentSaveInstanceStateDelegateImpl
 import pl.valueadd.mvi.fragment.mvi.BaseMviPresenter
 import pl.valueadd.mvi.fragment.mvi.IBaseView
 import pl.valueadd.mvi.fragment.mvi.IBaseViewState
 
 abstract class AbstractBackMviFragment<V : IBaseView<VS, *>, VS : IBaseViewState, VI : IBaseView.IBaseIntent, P : BaseMviPresenter<VS, *, *, V>>(@LayoutRes layoutId: Int) :
     BackMviFragment<V, VS, VI, P>(layoutId) {
 
+    protected val restoredViewState: VS?
+        get() = mviDelegate.restoredViewState
+
+    @Suppress("UNCHECKED_CAST")
+    override val mviDelegate: MviFragmentSaveInstanceStateDelegateImpl<V, VS>
+            by lazy {
+                MviFragmentSaveInstanceStateDelegateImpl(
+                    this as V,
+                    presenter
+                )
+            }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         DependencyUtil.inject(requireActivity(), this)
         super.onCreate(savedInstanceState)

app/src/main/java/pl/valueadd/mvi/example/presentation/base/AbstractBaseMviFragment.kt

@@ -4,13 +4,26 @@ import android.os.Bundle
 import androidx.annotation.LayoutRes
 import pl.valueadd.mvi.example.utility.dependencyinjection.DependencyUtil
 import pl.valueadd.mvi.fragment.base.BaseMviFragment
+import pl.valueadd.mvi.fragment.delegate.fragment.MviFragmentSaveInstanceStateDelegateImpl
 import pl.valueadd.mvi.fragment.mvi.BaseMviPresenter
 import pl.valueadd.mvi.fragment.mvi.IBaseView
 import pl.valueadd.mvi.fragment.mvi.IBaseViewState
 
 abstract class AbstractBaseMviFragment<V : IBaseView<VS, *>, VS : IBaseViewState, VI : IBaseView.IBaseIntent, P : BaseMviPresenter<VS, *, *, V>>(@LayoutRes layoutId: Int) :
     BaseMviFragment<V, VS, VI, P>(layoutId) {
 
+    protected val restoredViewState: VS?
+        get() = mviDelegate.restoredViewState
+
+    @Suppress("UNCHECKED_CAST")
+    override val mviDelegate: MviFragmentSaveInstanceStateDelegateImpl<V, VS>
+            by lazy {
+                MviFragmentSaveInstanceStateDelegateImpl(
+                    this as V,
+                    presenter
+                )
+            }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         DependencyUtil.inject(requireActivity(), this)
         super.onCreate(savedInstanceState)

app/src/main/java/pl/valueadd/mvi/example/presentation/main/first/FirstFragment.kt

@@ -24,8 +24,6 @@ class FirstFragment :
     @Inject
     override lateinit var presenter: FirstPresenter
 
-    override val shouldSaveViewStateInSavedInstanceState = true
-
     private val buttonDelay
         by lazy { resources.getInteger(R.integer.button_delay_100).toLong() }
 

mvi-valueadd/src/main/java/pl/valueadd/mvi/fragment/base/BaseMviFragment.kt

@@ -26,22 +26,9 @@ abstract class BaseMviFragment<V : IBaseView<VS, *>, VS : IBaseViewState, VI : I
     protected var disposables: CompositeDisposable =
         CompositeDisposable()
 
-    /*
-    * View state which can be restored after killing process by system.
-    */
-    protected val restoredViewState: VS?
-        get() = mviDelegate.restoredViewState
-
-    protected open val shouldSaveViewStateInSavedInstanceState = false
-
-    private val mviDelegate: MviFragmentDelegate<VS>
-        by lazy {
-            @Suppress("UNCHECKED_CAST")
-            MviFragmentDelegateImpl(
-                shouldSaveViewStateInSavedInstanceState,
-                this as V,
-                presenter)
-        }
+    @Suppress("UNCHECKED_CAST")
+    protected open val mviDelegate: MviFragmentDelegate
+            by lazy { MviFragmentDelegateImpl(this as V, presenter) }
 
     /* IBaseView */
 

mvi-valueadd/src/main/java/pl/valueadd/mvi/fragment/delegate/fragment/MviFragmentDelegate.kt

@@ -1,19 +1,16 @@
 package pl.valueadd.mvi.fragment.delegate.fragment
 
 import android.os.Bundle
-import pl.valueadd.mvi.fragment.mvi.IBaseViewState
 
-interface MviFragmentDelegate<VS : IBaseViewState> {
-
-    val restoredViewState: VS?
+interface MviFragmentDelegate {
 
     fun onCreate(savedInstanceState: Bundle?)
 
+    fun onSaveInstanceState(outState: Bundle)
+
     fun onStart()
 
     fun onStop()
 
     fun onDestroy()
-
-    fun onSaveInstanceState(outState: Bundle)
 }

mvi-valueadd/src/main/java/pl/valueadd/mvi/fragment/delegate/fragment/MviFragmentDelegateImpl.kt

@@ -3,25 +3,23 @@ package pl.valueadd.mvi.fragment.delegate.fragment
 import android.os.Bundle
 import pl.valueadd.mvi.fragment.mvi.BaseMviPresenter
 import pl.valueadd.mvi.fragment.mvi.IBaseView
-import pl.valueadd.mvi.fragment.mvi.IBaseViewState
 
-class MviFragmentDelegateImpl<V : IBaseView<VS, *>, VS : IBaseViewState>(
-    private val shouldHandleSaveInstanceState: Boolean,
-    private val fragment: V,
-    private val presenter: BaseMviPresenter<VS, *, *, V>
-) : MviFragmentDelegate<VS> {
+/**
+ * Minimal implementation of contract between fragment and presenter.
+ *
+ * This API requires call every fragment's lifecycle callback event defined at [MviFragmentDelegate].
+ */
+open class MviFragmentDelegateImpl<V : IBaseView<*, *>>(
+    protected val fragment: V,
+    protected val presenter: BaseMviPresenter<*, *, *, V>
+) : MviFragmentDelegate {
 
-    companion object {
-        private const val VIEW_STATE_BUNDLE_KEY = "VIEW_STATE_BUNDLE_KEY"
+    override fun onCreate(savedInstanceState: Bundle?) {
+        // no-op
     }
 
-    override var restoredViewState: VS? = null
-        private set
-
-    override fun onCreate(savedInstanceState: Bundle?) {
-        if (shouldHandleSaveInstanceState) {
-            this.restoredViewState = savedInstanceState?.getParcelable(VIEW_STATE_BUNDLE_KEY)
-        }
+    override fun onSaveInstanceState(outState: Bundle) {
+        // no-op
     }
 
     override fun onStart() {
@@ -32,12 +30,6 @@ class MviFragmentDelegateImpl<V : IBaseView<VS, *>, VS : IBaseViewState>(
         presenter.detachView()
     }
 
-    override fun onSaveInstanceState(outState: Bundle) {
-        if (shouldHandleSaveInstanceState) {
-            outState.putParcelable(VIEW_STATE_BUNDLE_KEY, presenter.currentState)
-        }
-    }
-
     override fun onDestroy() {
         presenter.destroy()
     }

mvi-valueadd/src/main/java/pl/valueadd/mvi/fragment/delegate/fragment/MviFragmentSaveInstanceStateDelegate.kt

@@ -0,0 +1,8 @@
+package pl.valueadd.mvi.fragment.delegate.fragment
+
+import pl.valueadd.mvi.fragment.mvi.IBaseViewState
+
+interface MviFragmentSaveInstanceStateDelegate<VS : IBaseViewState> {
+
+    val restoredViewState: VS?
+}

mvi-valueadd/src/main/java/pl/valueadd/mvi/fragment/delegate/fragment/MviFragmentSaveInstanceStateDelegateImpl.kt

@@ -0,0 +1,38 @@
+package pl.valueadd.mvi.fragment.delegate.fragment
+
+import android.os.Bundle
+import pl.valueadd.mvi.fragment.mvi.BaseMviPresenter
+import pl.valueadd.mvi.fragment.mvi.IBaseView
+import pl.valueadd.mvi.fragment.mvi.IBaseViewState
+
+/**
+ * Extended [implementation][MviFragmentDelegateImpl] of fragment's MVI which handles
+ * that state can be restored after killing process by system.
+ *
+ * @see MviFragmentDelegateImpl
+ */
+class MviFragmentSaveInstanceStateDelegateImpl<V : IBaseView<VS, *>, VS : IBaseViewState>(
+    fragment: V,
+    presenter: BaseMviPresenter<VS, *, *, V>
+) : MviFragmentDelegateImpl<V>(fragment, presenter),
+    MviFragmentSaveInstanceStateDelegate<VS> {
+
+    companion object {
+        private const val VIEW_STATE_BUNDLE_KEY = "VIEW_STATE_BUNDLE_KEY"
+    }
+
+    override var restoredViewState: VS? = null
+        private set
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        this.restoredViewState =
+            savedInstanceState?.getParcelable(VIEW_STATE_BUNDLE_KEY)
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        outState.putParcelable(
+            VIEW_STATE_BUNDLE_KEY,
+            presenter.currentState
+        )
+    }
+}