[BottomSheetBehavior] Apply the max width/height during measure instead of modifying layout params

Previously the BottomSheetBehavior was checking the measured size during onLayout and if it exceeded the max width or height configured it would "adjust" them by directly modifying the width and height on the layout params and then posting a setLayoutParams. This has many problems and is fundamentally the wrong way to do it. First off, a view should never modify the layout params that are configured on it for two reasons, one, they are properties of the parent view group, not the view itself, and two, they are almost always intended for users of the view group to configure, not the view group itself. Modifying the layout params directly is clobbering any previously configured parameter and permanently changing the layout (for example consider the case where the max width is set to 100dp and then later set to 200dp, the view would not be allowed to grow to 200dp because its layout params would already have been clobbered). Secondly the post is a very bad way to apply this max, not only does it trigger an entire layout pass a second time but it does so after having completed the first layout pass so it will cause the bottom sheet to render at the original size and then the capped size, it's both inefficient and will cause user visible jank.

The correct way to apply a maximum width/height is to do it during layout by incorporating it into the measure specs that are passed to the child. This doesn't clobber any state that the user of the view configured (i.e. when the parent measure specs change, e.g. due to screen rotation, the views correctly relayout) and it avoids doing multiple layout passes, the child can measure itself to the correct size the first time.

PiperOrigin-RevId: 387379138

Author: Material Design Team

lib/java/com/google/android/material/bottomsheet/BottomSheetBehavior.java

@@ -43,8 +43,10 @@
 import android.view.MotionEvent;
 import android.view.VelocityTracker;
 import android.view.View;
+import android.view.View.MeasureSpec;
 import android.view.ViewConfiguration;
 import android.view.ViewGroup;
+import android.view.ViewGroup.MarginLayoutParams;
 import android.view.ViewParent;
 import android.view.accessibility.AccessibilityEvent;
 import androidx.annotation.FloatRange;
@@ -194,9 +196,7 @@ public abstract static class BottomSheetCallback {
 
   private static final int CORNER_ANIMATION_DURATION = 500;
 
-  private static final int NO_WIDTH = -1;
-
-  private static final int NO_HEIGHT = -1;
+  private static final int NO_MAX_SIZE = -1;
 
   private boolean fitToContents = true;
 
@@ -221,9 +221,9 @@ public abstract static class BottomSheetCallback {
 
   private MaterialShapeDrawable materialShapeDrawable;
 
-  private int maxWidth = NO_WIDTH;
+  private int maxWidth = NO_MAX_SIZE;
 
-  private int maxHeight = NO_HEIGHT;
+  private int maxHeight = NO_MAX_SIZE;
 
   private int gestureInsetBottom;
   private boolean gestureInsetBottomIgnored;
@@ -326,13 +326,13 @@ public BottomSheetBehavior(@NonNull Context context, @Nullable AttributeSet attr
     if (a.hasValue(R.styleable.BottomSheetBehavior_Layout_android_maxWidth)) {
       setMaxWidth(
           a.getDimensionPixelSize(
-              R.styleable.BottomSheetBehavior_Layout_android_maxWidth, NO_WIDTH));
+              R.styleable.BottomSheetBehavior_Layout_android_maxWidth, NO_MAX_SIZE));
     }
 
     if (a.hasValue(R.styleable.BottomSheetBehavior_Layout_android_maxHeight)) {
       setMaxHeight(
           a.getDimensionPixelSize(
-              R.styleable.BottomSheetBehavior_Layout_android_maxHeight, NO_HEIGHT));
+              R.styleable.BottomSheetBehavior_Layout_android_maxHeight, NO_MAX_SIZE));
     }
 
     TypedValue value = a.peekValue(R.styleable.BottomSheetBehavior_Layout_behavior_peekHeight);
@@ -421,6 +421,62 @@ public void onDetachedFromLayoutParams() {
     viewDragHelper = null;
   }
 
+  @Override
+  public boolean onMeasureChild(
+      @NonNull CoordinatorLayout parent,
+      @NonNull V child,
+      int parentWidthMeasureSpec,
+      int widthUsed,
+      int parentHeightMeasureSpec,
+      int heightUsed) {
+    MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
+    int childWidthMeasureSpec =
+        getChildMeasureSpec(
+            parentWidthMeasureSpec,
+            parent.getPaddingLeft()
+                + parent.getPaddingRight()
+                + lp.leftMargin
+                + lp.rightMargin
+                + widthUsed,
+            maxWidth,
+            lp.width);
+    int childHeightMeasureSpec =
+        getChildMeasureSpec(
+            parentHeightMeasureSpec,
+            parent.getPaddingTop()
+                + parent.getPaddingBottom()
+                + lp.topMargin
+                + lp.bottomMargin
+                + heightUsed,
+            maxHeight,
+            lp.height);
+    child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
+    return true; // Child was measured
+  }
+
+  private int getChildMeasureSpec(
+      int parentMeasureSpec,
+      int padding,
+      int maxSize,
+      int childDimension) {
+    int result = ViewGroup.getChildMeasureSpec(parentMeasureSpec, padding, childDimension);
+    if (maxSize == NO_MAX_SIZE) {
+      return result;
+    } else {
+      int mode = MeasureSpec.getMode(result);
+      int size = MeasureSpec.getSize(result);
+      switch (mode) {
+        case MeasureSpec.EXACTLY:
+          return MeasureSpec.makeMeasureSpec(min(size, maxSize), MeasureSpec.EXACTLY);
+        case MeasureSpec.AT_MOST:
+        case MeasureSpec.UNSPECIFIED:
+        default:
+          return MeasureSpec.makeMeasureSpec(
+              size == 0 ? maxSize : min(size, maxSize), MeasureSpec.AT_MOST);
+      }
+    }
+  }
+
   @Override
   public boolean onLayoutChild(
       @NonNull CoordinatorLayout parent, @NonNull final V child, int layoutDirection) {
@@ -453,8 +509,6 @@ public boolean onLayoutChild(
           == ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_AUTO) {
         ViewCompat.setImportantForAccessibility(child, ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_YES);
       }
-
-      adjustChildWidthAndHeightIfNeeded(child);
     }
     if (viewDragHelper == null) {
       viewDragHelper = ViewDragHelper.create(parent, dragCallback);
@@ -1236,33 +1290,6 @@ void setStateInternal(@State int state) {
     updateAccessibilityActions();
   }
 
-  private void adjustChildWidthAndHeightIfNeeded(@NonNull final V child) {
-    final ViewGroup.LayoutParams lp = child.getLayoutParams();
-    boolean layoutHasChanges = false;
-
-    int width = child.getMeasuredWidth();
-    if (width > maxWidth && maxWidth != NO_WIDTH) {
-      lp.width = maxWidth;
-      layoutHasChanges = true;
-    }
-
-    int height = child.getMeasuredHeight();
-    if (height > maxHeight && maxHeight != NO_HEIGHT) {
-      lp.height = maxHeight;
-      layoutHasChanges = true;
-    }
-
-    if (layoutHasChanges) {
-      child.post(
-          new Runnable() {
-            @Override
-            public void run() {
-              child.setLayoutParams(lp);
-            }
-          });
-    }
-  }
-
   private void updateDrawableForTargetState(@State int state) {
     if (state == STATE_SETTLING) {
       // Special case: we want to know which state we're settling to, so wait for another call.