Remove onPreDrawListeners earlier in TextView

Bug 5556478

Launcher pre-populates its all apps and widget pages with their
content, which includes text. The layout calls some onMeasure methods
that trigger TextView's registerForPreDraw(), which in turns adds a
listener in the ViewTreeObserver.

However, some of these pages may never be actually displayed, leaving
the listeners in the list since onDraw() is never called.

As a result, every frame displayed by launcher is slowned down by this
array copy of 6-18 listeners.

The problem is not Launcher specific since other applications may use
a similar caching mechanism.

The solution is to unsubscribe the listener in onPreDraw.

The drawback is that several successive calls to registerForPreDraw() will
add/remove the some listener object. However, these calls are rare and are
relatively cheap since we're just adding the object in and out of an
ArrayList which should not need to change its size.

Change-Id: Ifb65655a27e302d31a2ad622d18f839aec99689e

1 files changed, 10 insertions, 28 deletions

diff --git a/core/java/android/widget/TextView.java b/core/java/android/widget/TextView.java
index 40d8a779c914..3ce0a3e2c9bb 100644
--- a/core/java/android/widget/TextView.java
+++ b/core/java/android/widget/TextView.java
@@ -256,10 +256,7 @@ public class TextView extends View implements ViewTreeObserver.OnPreDrawListener
 
     private float mShadowRadius, mShadowDx, mShadowDy;
 
-    private static final int PREDRAW_NOT_REGISTERED = 0;
-    private static final int PREDRAW_PENDING = 1;
-    private static final int PREDRAW_DONE = 2;
-    private int mPreDrawState = PREDRAW_NOT_REGISTERED;
+    private boolean mPreDrawRegistered;
 
     private TextUtils.TruncateAt mEllipsize = null;
 
@@ -4387,26 +4384,16 @@ public class TextView extends View implements ViewTreeObserver.OnPreDrawListener
     }
 
     private void registerForPreDraw() {
-        final ViewTreeObserver observer = getViewTreeObserver();
-
-        if (mPreDrawState == PREDRAW_NOT_REGISTERED) {
-            observer.addOnPreDrawListener(this);
-            mPreDrawState = PREDRAW_PENDING;
-        } else if (mPreDrawState == PREDRAW_DONE) {
-            mPreDrawState = PREDRAW_PENDING;
+        if (!mPreDrawRegistered) {
+            getViewTreeObserver().addOnPreDrawListener(this);
+            mPreDrawRegistered = true;
         }
-
-        // else state is PREDRAW_PENDING, so keep waiting.
     }
 
     /**
      * {@inheritDoc}
      */
     public boolean onPreDraw() {
-        if (mPreDrawState != PREDRAW_PENDING) {
-            return true;
-        }
-
         if (mLayout == null) {
             assumeLayout();
         }
@@ -4457,7 +4444,9 @@ public class TextView extends View implements ViewTreeObserver.OnPreDrawListener
             startSelectionActionMode();
         }
 
-        mPreDrawState = PREDRAW_DONE;
+        getViewTreeObserver().removeOnPreDrawListener(this);
+        mPreDrawRegistered = false;
+
         return !changed;
     }
 
@@ -4492,10 +4481,9 @@ public class TextView extends View implements ViewTreeObserver.OnPreDrawListener
     protected void onDetachedFromWindow() {
         super.onDetachedFromWindow();
 
-        final ViewTreeObserver observer = getViewTreeObserver();
-        if (mPreDrawState != PREDRAW_NOT_REGISTERED) {
-            observer.removeOnPreDrawListener(this);
-            mPreDrawState = PREDRAW_NOT_REGISTERED;
+        if (mPreDrawRegistered) {
+            getViewTreeObserver().removeOnPreDrawListener(this);
+            mPreDrawRegistered = false;
         }
 
         if (mError != null) {
@@ -4768,12 +4756,6 @@ public class TextView extends View implements ViewTreeObserver.OnPreDrawListener
 
     @Override
     protected void onDraw(Canvas canvas) {
-        if (mPreDrawState == PREDRAW_DONE) {
-            final ViewTreeObserver observer = getViewTreeObserver();
-            observer.removeOnPreDrawListener(this);
-            mPreDrawState = PREDRAW_NOT_REGISTERED;
-        }
-
         if (mCurrentAlpha <= ViewConfiguration.ALPHA_THRESHOLD_INT) return;
 
         restartMarqueeIfNeeded();