kuno · April 5, 2019 14:30 · Jan 31, 2019 · Jan 31, 2019
diff --git a/attrs.xml b/attrs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <declare-styleable name="DialogNavigator">
+        <attr name="android:name"/>
+    </declare-styleable>
+</resources>
diff --git a/DialogNavigator.kt b/DialogNavigator.kt
@@ -0,0 +1,168 @@
+package com.geekorum.geekdroid.navigation
+
+import android.content.Context
+import android.os.Bundle
+import android.util.AttributeSet
+import androidx.core.content.res.use
+import androidx.core.os.bundleOf
+import androidx.fragment.app.DialogFragment
+import androidx.fragment.app.Fragment
+import androidx.fragment.app.FragmentManager
+import androidx.navigation.NavDestination
+import androidx.navigation.NavOptions
+import androidx.navigation.Navigator
+import androidx.navigation.fragment.FragmentNavigator
+import androidx.navigation.fragment.NavHostFragment
+import androidx.navigation.plusAssign
+import com.geekorum.geekdroid.R
+import java.util.ArrayDeque
+import java.util.Deque
+
+/**
+ * Allows to navigate to some [DialogFragment].
+ *
+ * Usage: add some dialog element in your navigation graph
+ * ```
+ *     <dialog android:id="@+id/my_dialog"
+ *               android:name="com.exemple.MyDialogFragment"/>
+ *
+ * ```
+ * Use [DialogNavHostFragment] as your [androidx.navigation.NavHost] in your layout
+ * or add the DialogNavigator to your [NavigatorProvider]
+ */
+@Navigator.Name("dialog")
+class DialogNavigator(
+    private val context: Context,
+    private val fragmentManager: FragmentManager
+) : Navigator<DialogNavigator.Destination>() {
+
+    private var lastBackStackEntry: FragmentManager.BackStackEntry? = null
+    private val backstack: Deque<Int> = ArrayDeque()
+    private var pendingPopBackStack = false
+
+    private val onBackstackChangedListener: FragmentManager.OnBackStackChangedListener =
+        FragmentManager.OnBackStackChangedListener {
+            if (pendingPopBackStack) {
+                val entry = fragmentManager.findLastBackStackEntry { it.name == FRAGMENT_BACKSTACK_NAME }
+                pendingPopBackStack = (entry != null && entry == lastBackStackEntry)
+                lastBackStackEntry = entry
+                return@OnBackStackChangedListener
+            }
+            if (lastBackStackEntry != null && fragmentManager.noneBackStackEntry { it == lastBackStackEntry }) {
+                backstack.removeLast()
+            }
+            lastBackStackEntry = fragmentManager.findLastBackStackEntry { it.name == FRAGMENT_BACKSTACK_NAME }
+        }
+
+    override fun navigate(
+        destination: Destination, args: Bundle?, navOptions: NavOptions?, navigatorExtras: Extras?
+    ): NavDestination? {
+        val lastDialogFragment = instantiateFragment(destination.className!!, args)
+        val tr = fragmentManager.beginTransaction().addToBackStack(FRAGMENT_BACKSTACK_NAME)
+
+        lastDialogFragment.show(tr, destination.id.toString())
+        backstack.addLast(destination.id)
+
+        // we don't want the destination to be added to the NavController stack,
+        // because it will update the whole
+        // navigation chrome (global AppBar, NavigationView, etc)
+        return null
+    }
+
+    private fun instantiateFragment(className: String, args: Bundle?): DialogFragment {
+        return Fragment.instantiate(context, className, args) as DialogFragment
+    }
+
+    override fun createDestination(): Destination = Destination(this)
+
+    override fun popBackStack(): Boolean {
+        val lastDialogFragment =
+            fragmentManager.findFragmentByTag(backstack.lastOrNull()?.toString()) as? DialogFragment ?: return false
+        lastDialogFragment.dismiss()
+        backstack.removeLast()
+        pendingPopBackStack = true
+        return true
+    }
+
+    /* These 2 lifecycle methods should be handled in the NavHost of this navigator.
+     * When the NavHost add them it should configure them or call some method so
+     * that they can configure there listeners. However, this make a strong coupling between a Navigator and
+     * its host implementation.
+     *
+     * The NavigatorProvider of NavController add a Navigator.OnBackStackChangedListener
+     * who calls these methods */
+    override fun onBackPressAdded() {
+        fragmentManager.addOnBackStackChangedListener(onBackstackChangedListener)
+    }
+
+    override fun onBackPressRemoved() {
+        fragmentManager.removeOnBackStackChangedListener(onBackstackChangedListener)
+    }
+
+    override fun onSaveState(): Bundle? {
+        return bundleOf(KEY_BACKSTACK_ID to backstack.toIntArray())
+    }
+
+    override fun onRestoreState(savedState: Bundle) {
+        savedState.getIntArray(KEY_BACKSTACK_ID)?.let {
+            backstack.clear()
+            for (id in it) {
+                backstack.addLast(id)
+            }
+        }
+        lastBackStackEntry = fragmentManager.findLastBackStackEntry { it.name == FRAGMENT_BACKSTACK_NAME }
+    }
+
+    class Destination(navigator: DialogNavigator) : NavDestination(navigator) {
+        var className: String? = null
+            get() = checkNotNull(field) { "Dialog name was not set" }
+
+        override fun onInflate(context: Context, attrs: AttributeSet) {
+            super.onInflate(context, attrs)
+            context.resources.obtainAttributes(attrs, R.styleable.DialogNavigator).use {
+                className = it.getString(R.styleable.DialogNavigator_android_name)
+            }
+        }
+    }
+
+    companion object {
+        private const val KEY_BACKSTACK_ID = "com.geekorum.geekdroid:navigation:backstack_ids"
+        private const val FRAGMENT_BACKSTACK_NAME = "com.geekorum.geekdroid:navigation:backstack"
+    }
+
+    private inline fun FragmentManager.findLastBackStackEntry(
+        predicate: (FragmentManager.BackStackEntry) -> Boolean
+    ): FragmentManager.BackStackEntry? {
+        for (i in backStackEntryCount - 1 downTo 0) {
+            val backStackEntry = getBackStackEntryAt(i)
+            if (predicate(backStackEntry)) {
+                return backStackEntry
+            }
+        }
+        return null
+    }
+
+    private inline fun FragmentManager.noneBackStackEntry(
+        predicate: (FragmentManager.BackStackEntry) -> Boolean
+    ): Boolean {
+        for (i in 0 until backStackEntryCount) {
+            val backStackEntry = getBackStackEntryAt(i)
+            if (predicate(backStackEntry)) {
+                return false
+            }
+        }
+        return true
+    }
+}
+
+
+/**
+ * A [NavHostFragment] who supports navigation to [DialogFragment].
+ */
+class DialogNavHostFragment : NavHostFragment() {
+
+    override fun createFragmentNavigator(): Navigator<out FragmentNavigator.Destination> {
+        navController.navigatorProvider += DialogNavigator(requireContext(), childFragmentManager)
+        return super.createFragmentNavigator()
+    }
+}