Fix crashing of font size settings screen due to the timing

of initialization of ExploreByTouchHelper
Bug: 27674946

Change-Id: Ief92b5db975861aa31029712854e78edf4454eb5

src/com/android/settings/widget/LabeledSeekBar.java

@@ -139,6 +139,9 @@ public class LabeledSeekBar extends SeekBar {
 
     private ExploreByTouchHelper mAccessHelper;
 
+    private boolean mOnMeasureCalled;
+    private boolean mOnAttachedWindowCalled;
+
     public LabeledSeekBar(Context context, AttributeSet attrs) {
         this(context, attrs, com.android.internal.R.attr.seekBarStyle);
     }
@@ -204,11 +207,18 @@ public class LabeledSeekBar extends SeekBar {
         super.setOnSeekBarChangeListener(l2);
     }
 
+    @Override
+    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
+        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
+        mOnMeasureCalled = true;
+        tryInitAccessHelper();
+    }
+
     @Override
     protected void onAttachedToWindow() {
         super.onAttachedToWindow();
-        mAccessHelper = new LabeledSeekBarExploreByTouchHelper(this);
-        ViewCompat.setAccessibilityDelegate(this, mAccessHelper);
+        mOnAttachedWindowCalled = true;
+        tryInitAccessHelper();
     }
 
     @Override
@@ -227,6 +237,18 @@ public class LabeledSeekBar extends SeekBar {
         return super.dispatchHoverEvent(event);
     }
 
+    /**
+     * Initialize accessibility delegation only when both onAttachedWindow and onMeasure
+     * has been called.
+     */
+    private void tryInitAccessHelper() {
+        if (mOnAttachedWindowCalled && mOnMeasureCalled) {
+            mAccessHelper = new LabeledSeekBarExploreByTouchHelper(this);
+            ViewCompat.setAccessibilityDelegate(this, mAccessHelper);
+            mOnAttachedWindowCalled = mOnMeasureCalled = false;
+        }
+    }
+
     private void sendClickEventForAccessibility(int progress) {
         if (mAccessHelper != null) {
             mAccessHelper.invalidateRoot();