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      1 /*
      2  * Copyright (C) 2017 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package androidx.wear.widget.drawer;
     18 
     19 import android.os.Handler;
     20 import android.os.Looper;
     21 import android.view.View;
     22 import android.view.View.OnScrollChangeListener;
     23 import android.widget.ScrollView;
     24 
     25 import androidx.annotation.RestrictTo;
     26 import androidx.annotation.RestrictTo.Scope;
     27 import androidx.wear.widget.drawer.FlingWatcherFactory.FlingListener;
     28 import androidx.wear.widget.drawer.FlingWatcherFactory.FlingWatcher;
     29 
     30 import java.lang.ref.WeakReference;
     31 
     32 /**
     33  * {@link FlingWatcher} implementation for {@link ScrollView ScrollViews}.
     34  * <p>
     35  * Because {@link ScrollView} does not provide a way to listen to the scroll state, there's no
     36  * callback which definitely indicates the fling has finished. So, we instead listen for scroll
     37  * events. If we reach the top or bottom of the view or if there are no events within {@link
     38  * #MAX_WAIT_TIME_MS}, we assume the fling has finished.
     39  *
     40  * @hide
     41  */
     42 @RestrictTo(Scope.LIBRARY)
     43 class ScrollViewFlingWatcher implements FlingWatcher, OnScrollChangeListener {
     44 
     45     static final int MAX_WAIT_TIME_MS = 100;
     46     private final Handler mMainThreadHandler = new Handler(Looper.getMainLooper());
     47     private final FlingListener mListener;
     48     private final WeakReference<ScrollView> mScrollView;
     49     private final Runnable mNotifyListenerRunnable = new Runnable() {
     50         @Override
     51         public void run() {
     52             onEndOfFlingFound();
     53         }
     54     };
     55 
     56     ScrollViewFlingWatcher(FlingListener listener, ScrollView scrollView) {
     57         mListener = listener;
     58         mScrollView = new WeakReference<>(scrollView);
     59     }
     60 
     61     private static boolean isViewAtTopOrBottom(View view) {
     62         return !view.canScrollVertically(-1 /* up */) || !view.canScrollVertically(1 /* down */);
     63     }
     64 
     65     @Override
     66     public void watch() {
     67         ScrollView scrollView = mScrollView.get();
     68         if (scrollView != null) {
     69             scrollView.setOnScrollChangeListener(this);
     70             scheduleNext();
     71         }
     72     }
     73 
     74     @Override
     75     public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX,
     76             int oldScrollY) {
     77         if (isViewAtTopOrBottom(v)) {
     78             onEndOfFlingFound();
     79         } else {
     80             scheduleNext();
     81         }
     82     }
     83 
     84     private void onEndOfFlingFound() {
     85         mMainThreadHandler.removeCallbacks(mNotifyListenerRunnable);
     86 
     87         ScrollView scrollView = mScrollView.get();
     88         if (scrollView != null) {
     89             scrollView.setOnScrollChangeListener(null);
     90             mListener.onFlingComplete(scrollView);
     91         }
     92     }
     93 
     94     private void scheduleNext() {
     95         mMainThreadHandler.removeCallbacks(mNotifyListenerRunnable);
     96         mMainThreadHandler.postDelayed(mNotifyListenerRunnable, MAX_WAIT_TIME_MS);
     97     }
     98 }
     99