fix the gone behavour in MotionLayout (#504)

* fix the gone behavour in MotionLayout

* fix comments

* comments 2

constraintlayout/constraintlayout/src/main/java/androidx/constraintlayout/motion/widget/MotionLayout.java

@@ -2606,6 +2606,7 @@ private void setupConstraintWidget(ConstraintWidgetContainer base, ConstraintSet
             }
             //  build id widget map
             for (ConstraintWidget child : base.getChildren()) {
+                child.setAnimated(true);
                 View view = (View) child.getCompanionWidget();
                 mapIdToWidget.put(view.getId(), child);
             }

constraintlayout/core/src/main/java/androidx/constraintlayout/core/widgets/ConstraintWidget.java

@@ -481,7 +481,8 @@ public enum DimensionBehaviour {
 
     // Contains the visibility status of the widget (VISIBLE, INVISIBLE, or GONE)
     private int mVisibility = VISIBLE;
-
+    // Contains if this widget is animated. Currently only affects gone behaviour
+    private boolean mAnimated = false;
     private String mDebugName = null;
     private String mType = null;
 
@@ -922,6 +923,24 @@ public int getVisibility() {
         return mVisibility;
     }
 
+    /**
+     * Set if this widget is animated. Currently only affects gone behaviour
+     *
+     * @param animated if true the widget must be positioned correctly when not visible
+     */
+    public void setAnimated(boolean animated) {
+        mAnimated = animated;
+    }
+
+    /**
+     * Returns if this widget is animated. Currently only affects gone behaviour
+     *
+     * @return true if ConstraintWidget is used in Animation
+     */
+    public boolean isAnimated() {
+        return mAnimated;
+    }
+
     /**
      * Returns the name of this widget (used for debug purposes)
      *
@@ -2417,8 +2436,8 @@ public void addToSolver(LinearSystem system, boolean optimize) {
             }
         }
 
-        if (mVisibility == GONE && !hasDependencies()
-                && !mIsInBarrier[HORIZONTAL] && !mIsInBarrier[VERTICAL]) {
+        if (!(mVisibility != GONE ||  mAnimated || hasDependencies() ||
+                mIsInBarrier[HORIZONTAL] ||  mIsInBarrier[VERTICAL])) {
             return;
         }
 
@@ -3426,6 +3445,7 @@ public void copy(ConstraintWidget src, HashMap<ConstraintWidget, ConstraintWidge
         mCompanionWidget = src.mCompanionWidget;
         mContainerItemSkip = src.mContainerItemSkip;
         mVisibility = src.mVisibility;
+        mAnimated = src.mAnimated;
         mDebugName = src.mDebugName;
         mType = src.mType;
 

projects/MotionLayoutVerification/app/src/main/res/layout/bug_015.xml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.motion.widget.MotionLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:id="@+id/rootView"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:background="#BECEED"
+    app:layoutDescription="@xml/bug_006_scene"
+    tools:context=".OnCreateTransiton"
+    >
+    <View
+        android:id="@+id/view"
+        android:layout_width="100dp"
+        android:layout_height="10dp"
+        android:background="#4B1A8F"
+
+        app:layout_constraintVertical_bias="0"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
+    <View
+        android:id="@+id/view2"
+        android:layout_width="100dp"
+        android:layout_height="10dp"
+        android:background="#790"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintTop_toTopOf="parent"/>
+</androidx.constraintlayout.motion.widget.MotionLayout>

projects/MotionLayoutVerification/app/src/main/res/xml/bug_015_scene.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<MotionScene xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:motion="http://schemas.android.com/apk/res-auto">
+
+    <ConstraintSet android:id="@+id/end">
+        <Constraint android:id="@+id/view"
+            android:layout_width="100dp"
+            android:layout_height="10dp"
+            android:visibility="visible"
+            motion:layout_constraintVertical_bias="1"
+            motion:layout_constraintStart_toStartOf="parent"
+            motion:layout_constraintBottom_toBottomOf="parent"
+            motion:layout_constraintEnd_toEndOf="parent"
+            motion:layout_constraintTop_toTopOf="parent" />
+
+    </ConstraintSet>
+
+    <ConstraintSet android:id="@+id/start">
+    </ConstraintSet>
+
+    <Transition
+        motion:constraintSetStart="@id/start"
+        motion:constraintSetEnd="@id/end"
+        motion:duration="1000">
+        <OnClick />
+        <KeyFrameSet>
+            <KeyTrigger motion:framePosition="50" motion:motionTarget="@+id/view" motion:triggerId="@id/foo" />
+        </KeyFrameSet>
+    </Transition>
+
+</MotionScene>