Closes #4536: Add View.findViewHierarchy()

This allows EngineViewBottomBehavior.onDependentViewChanged() to call setVerticalClipping on any nested EngineView

components/feature/session/src/main/java/mozilla/components/feature/session/behavior/EngineViewBottomBehavior.kt

@@ -10,6 +10,7 @@ import android.util.AttributeSet
 import android.view.View
 import androidx.coordinatorlayout.widget.CoordinatorLayout
 import mozilla.components.concept.engine.EngineView
+import mozilla.components.support.ktx.android.view.findViewInHierarchy
 
 /**
  * A [CoordinatorLayout.Behavior] implementation to be used with [EngineView] when placing a toolbar at the
@@ -37,8 +38,13 @@ class EngineViewBottomBehavior(
         return super.layoutDependsOn(parent, child, dependency)
     }
 
+    /**
+     * Apply vertical clipping to [EngineView]. This requires [EngineViewBottomBehavior] to be set
+     * in/on the [EngineView] or its parent. Must be a direct descending child of [CoordinatorLayout].
+     */
     override fun onDependentViewChanged(parent: CoordinatorLayout, child: View, dependency: View): Boolean {
-        (child as EngineView).setVerticalClipping(dependency.height - dependency.translationY.toInt())
+        val engineView = child.findViewInHierarchy { it is EngineView } as EngineView?
+        engineView?.setVerticalClipping(dependency.height - dependency.translationY.toInt())
         return true
     }
 }

components/support/ktx/src/main/java/mozilla/components/support/ktx/android/view/View.kt

@@ -9,6 +9,7 @@ import android.graphics.Rect
 import android.os.Handler
 import android.os.Looper
 import android.view.View
+import android.view.ViewGroup
 import android.view.ViewTreeObserver
 import android.view.inputmethod.InputMethodManager
 import androidx.annotation.MainThread
@@ -105,6 +106,22 @@ fun View.toScope(): CoroutineScope {
     return scope
 }
 
+/**
+ * Finds the first a view in the hierarchy, for which the provided predicate is true.
+ */
+fun View.findViewInHierarchy(predicate: (View) -> Boolean): View? {
+    if (predicate(this)) return this
+
+    if (this is ViewGroup) {
+        for (i in 0 until this.childCount) {
+            val childView = this.getChildAt(i).findViewInHierarchy(predicate)
+            if (childView != null) return childView
+        }
+    }
+
+    return null
+}
+
 /**
  * Registers a one-time callback to be invoked when the global layout state
  * or the visibility of views within the view tree changes.

components/support/ktx/src/test/java/mozilla/components/support/ktx/android/view/ViewTest.kt

@@ -5,9 +5,12 @@
 package mozilla.components.support.ktx.android.view
 
 import android.app.Activity
+import android.content.Context
 import android.view.View
 import android.view.WindowManager
 import android.widget.EditText
+import android.widget.LinearLayout
+import android.widget.RelativeLayout
 import android.widget.TextView
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import kotlinx.coroutines.Dispatchers
@@ -23,6 +26,7 @@ import mozilla.components.support.test.robolectric.testContext
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNotNull
 import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
@@ -183,4 +187,31 @@ class ViewTest {
         assertFalse(latch.await(5, TimeUnit.SECONDS))
         assertFalse(coroutineExecuted)
     }
+
+    @Test
+    fun `correct view is found in the hierarchy matching the predicate`() {
+        val root = LinearLayout(testContext)
+        val layout = RelativeLayout(testContext)
+        val testView = TestView(testContext)
+
+        layout.addView(testView)
+        root.addView(layout)
+
+        val rootFound = root.findViewInHierarchy { it is LinearLayout }
+
+        assertNotNull(rootFound)
+        assertTrue(rootFound is LinearLayout)
+
+        val layoutFound = root.findViewInHierarchy { it is RelativeLayout }
+
+        assertNotNull(layoutFound)
+        assertTrue(layoutFound is RelativeLayout)
+
+        val testViewFound = root.findViewInHierarchy { it is TestView }
+
+        assertNotNull(testViewFound)
+        assertTrue(testViewFound is TestView)
+    }
+
+    private class TestView(context: Context) : View(context)
 }