Add haptic effect for the seekbar in Settings 4/n.

- in Font size/Display size, perform haptic feedback as the seekbar's progress value is updated.
- screenshot, https://screenshot.googleplex.com/6tcD7a9hvCcWaui
- screenshot, https://screenshot.googleplex.com/89y4Q3RXskyajnL

Bug: 174109628
Test: make -j42 RunSettingsRoboTests ROBOTEST_FILTER=LabeledSeekBarTest
Change-Id: I7aff859e4fdaed6fe95a5d77564059ef1a7f6ff0

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

@@ -16,6 +16,8 @@
 
 package com.android.settings.widget;
 
+import static android.view.HapticFeedbackConstants.CLOCK_TICK;
+
 import android.content.Context;
 import android.graphics.Rect;
 import android.os.Bundle;
@@ -48,6 +50,8 @@ public class LabeledSeekBar extends SeekBar {
     /** Labels for discrete progress values. */
     private String[] mLabels;
 
+    private int mLastProgress = -1;
+
     public LabeledSeekBar(Context context, AttributeSet attrs) {
         this(context, attrs, com.android.internal.R.attr.seekBarStyle);
     }
@@ -118,6 +122,10 @@ public class LabeledSeekBar extends SeekBar {
                 mOnSeekBarChangeListener.onProgressChanged(seekBar, progress, fromUser);
                 sendClickEventForAccessibility(progress);
             }
+            if (progress != mLastProgress) {
+                seekBar.performHapticFeedback(CLOCK_TICK);
+                mLastProgress = progress;
+            }
         }
     };
 

tests/robotests/src/com/android/settings/widget/LabeledSeekBarTest.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.widget;
+
+import static android.view.HapticFeedbackConstants.CLOCK_TICK;
+import static android.view.HapticFeedbackConstants.CONTEXT_CLICK;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import static org.robolectric.Shadows.shadowOf;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.widget.SeekBar;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.RuntimeEnvironment;
+
+@RunWith(RobolectricTestRunner.class)
+public class LabeledSeekBarTest {
+
+    private Context mContext;
+    private AttributeSet mAttrs;
+    private SeekBar mSeekBar;
+    private LabeledSeekBar mLabeledSeekBar;
+    private SeekBar.OnSeekBarChangeListener mProxySeekBarListener;
+
+    @Before
+    public void setUp() {
+        mContext = RuntimeEnvironment.application;
+        mSeekBar = new SeekBar(mContext, mAttrs);
+        mLabeledSeekBar = new LabeledSeekBar(mContext, mAttrs);
+        mProxySeekBarListener = shadowOf(mLabeledSeekBar).getOnSeekBarChangeListener();
+    }
+
+    @Test
+    public void onProgressChanged_minimumValue_clockTickFeedbackPerformed() {
+        mSeekBar.performHapticFeedback(CONTEXT_CLICK);
+        mProxySeekBarListener.onProgressChanged(mSeekBar, 0, true);
+
+        assertThat(shadowOf(mSeekBar).lastHapticFeedbackPerformed()).isEqualTo(CLOCK_TICK);
+    }
+}