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      1 /*
      2  * Copyright (C) 2016 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 com.android.launcher3.util;
     18 
     19 import android.content.Context;
     20 import android.view.MotionEvent;
     21 import android.view.VelocityTracker;
     22 import android.view.View;
     23 import android.view.ViewConfiguration;
     24 
     25 public class VerticalFlingDetector implements View.OnTouchListener {
     26 
     27     private static final float CUSTOM_SLOP_MULTIPLIER = 2.2f;
     28     private static final int SEC_IN_MILLIS = 1000;
     29 
     30     private VelocityTracker mVelocityTracker;
     31     private float mMinimumFlingVelocity;
     32     private float mMaximumFlingVelocity;
     33     private float mDownX, mDownY;
     34     private boolean mShouldCheckFling;
     35     private double mCustomTouchSlop;
     36 
     37     public VerticalFlingDetector(Context context) {
     38         ViewConfiguration vc = ViewConfiguration.get(context);
     39         mMinimumFlingVelocity = vc.getScaledMinimumFlingVelocity();
     40         mMaximumFlingVelocity = vc.getScaledMaximumFlingVelocity();
     41         mCustomTouchSlop = CUSTOM_SLOP_MULTIPLIER * vc.getScaledTouchSlop();
     42     }
     43 
     44     @Override
     45     public boolean onTouch(View v, MotionEvent ev) {
     46         if (mVelocityTracker == null) {
     47             mVelocityTracker = VelocityTracker.obtain();
     48         }
     49         mVelocityTracker.addMovement(ev);
     50         switch (ev.getAction()) {
     51             case MotionEvent.ACTION_DOWN:
     52                 mDownX = ev.getX();
     53                 mDownY = ev.getY();
     54                 mShouldCheckFling = false;
     55                 break;
     56             case MotionEvent.ACTION_MOVE:
     57                 if (mShouldCheckFling) {
     58                     break;
     59                 }
     60                 if (Math.abs(ev.getY() - mDownY) > mCustomTouchSlop &&
     61                         Math.abs(ev.getY() - mDownY) > Math.abs(ev.getX() - mDownX)) {
     62                     mShouldCheckFling = true;
     63                 }
     64                 break;
     65             case MotionEvent.ACTION_UP:
     66                 if (mShouldCheckFling) {
     67                     mVelocityTracker.computeCurrentVelocity(SEC_IN_MILLIS, mMaximumFlingVelocity);
     68                     // only when fling is detected in down direction
     69                     if (mVelocityTracker.getYVelocity() > mMinimumFlingVelocity) {
     70                         cleanUp();
     71                         return true;
     72                     }
     73                 }
     74                 // fall through.
     75             case MotionEvent.ACTION_CANCEL:
     76                 cleanUp();
     77         }
     78         return false;
     79     }
     80 
     81     private void cleanUp() {
     82         if (mVelocityTracker == null) {
     83             return;
     84         }
     85         mVelocityTracker.recycle();
     86         mVelocityTracker = null;
     87     }
     88 }
     89