Android手势操作

前言

利用手势操作在现在的APP中越来越普及，大多数时候使用Fling，Scroll等Gesture能大幅度提高用户的操作体验，特别是大屏手机返回键程越来越大的现状下。
在Android系统下，手势识别是通过GestureDetector.OnGestureListener接口实现的，不过官方的文档可能觉得这部分 太基础和简单了，所以官方的API文档中对手势的讲解描述的都很简单，API Demo中也没有提供一个清楚的例子，所以自己总结一下，其中还是涉及不少的基础知识和一些官方文档中说明不清的地方，如果不能好好掌握这些基础知识，做 起事情来难免要吃一些苦头。言归正传，下面我们开始：

基础知识

我们先来明确一些概念，首先，Android的事件处理机制是基于Listener（监听器）来实现的，比我们今天所说的触摸屏相关的事件，就是通 过onTouchListener。其次，所有View的子类都可以通过setOnTouchListener()、 setOnKeyListener()等方法来添加对某一类事件的监听器。第三，Listener一般会以Interface（接口）的方式来提供，其中 包含一个或多个abstract（抽象）方法，我们需要实现这些方法来完成onTouch()、onKey()等等的操作。这样，当我们给某个view设 置了事件Listener，并实现了其中的抽象方法以后，程序便可以在特定的事件被dispatch到该view的时候，通过callbakc函数给予适 当的响应。

这篇文章简单介绍了事件触发的过程：Android事件分发图解

实作

我们现在实作一个使用手势的例子。
我们给RelativeView的实例my_view设定了一个onTouchListener，因为GestureTest类实现了 OnTouchListener 接口，所以简单的给一个this作为参数即可。onTouch方法则是实现了OnTouchListener中的抽象方法，我们只要在这里添加逻辑代码即 可在用户触摸屏幕时做出响应，

public class MainActivity extends ActionBarActivity implements View.OnTouchListener,GestureDetector.OnGestureListener{  GestureDetector gestureDetector = null;    @Override  protected void onCreate(Bundle savedInstanceState) {      super.onCreate(savedInstanceState);      setContentView(R.layout.activity_main);        gestureDetector = new GestureDetector(this);      gestureDetector.setIsLongpressEnabled(true);      View v = findViewById(R.id.my_view);      v.setOnTouchListener(this);  }      @Override  public boolean onCreateOptionsMenu(Menu menu) {      // Inflate the menu; this adds items to the action bar if it is present.      getMenuInflater().inflate(R.menu.menu_main, menu);      return true;  }    @Override  public boolean onOptionsItemSelected(MenuItem item) {      // Handle action bar item clicks here. The action bar will      // automatically handle clicks on the Home/Up button, so long      // as you specify a parent activity in AndroidManifest.xml.      int id = item.getItemId();        //noinspection SimplifiableIfStatement      if (id == R.id.action_settings) {          return true;      }        return super.onOptionsItemSelected(item);  }    @Override  public boolean onTouch(View view, MotionEvent motionEvent) {      Log.i("HYY","onTouch present");        return gestureDetector.onTouchEvent(motionEvent);  }    @Override  public boolean onDown(MotionEvent motionEvent) {      Log.i("HYY","onDown present");      return true;  }    @Override  public void onShowPress(MotionEvent motionEvent) {      Log.i("HYY","onShowPress present");  }    @Override  public boolean onSingleTapUp(MotionEvent motionEvent) {      Log.i("HYY","onSingleTapUp present");      return false;  }    @Override  public boolean onScroll(MotionEvent motionEvent, MotionEvent motionEvent2, float v, float v2) {      Log.i("HYY","onScroll present");      return false;  }    @Override  public void onLongPress(MotionEvent motionEvent) {      Log.i("HYY","onLongPress present");    }    @Override  public boolean onFling(MotionEvent motionEvent, MotionEvent motionEvent2, float v, float v2) {      Log.i("HYY","onFling present");      return false;  }  }

特别提示

这里有一点需要特别注意:要触发onScroll和onFling,必须让监听器的onDown的返回值设为true

那么为什么如果不把onDown的返回值设为true的话，onScroll和onFiling就都不会被触发呢？我们来看一下源码中的介绍

/**           * Notified when a scroll occurs with the initial on down {@link MotionEvent} and the           * current move {@link MotionEvent}. The distance in x and y is also supplied for           * convenience.           *           * @param e1 The first down motion event that started the scrolling.           * @param e2 The move motion event that triggered the current onScroll.           * @param distanceX The distance along the X axis that has been scrolled since the last           *              call to onScroll. This is NOT the distance between {@code e1}           *              and {@code e2}.           * @param distanceY The distance along the Y axis that has been scrolled since the last           *              call to onScroll. This is NOT the distance between {@code e1}           *              and {@code e2}.           * @return true if the event is consumed, else false           */          boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY);            /**           * Notified of a fling event when it occurs with the initial on down {@link MotionEvent}           * and the matching up {@link MotionEvent}. The calculated velocity is supplied along           * the x and y axis in pixels per second.           *           * @param e1 The first down motion event that started the fling.           * @param e2 The move motion event that triggered the current onFling.           * @param velocityX The velocity of this fling measured in pixels per second           *              along the x axis.           * @param velocityY The velocity of this fling measured in pixels per second           *              along the y axis.           * @return true if the event is consumed, else false           */          boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY);

onScroll和onFling方法的注释上写的很清楚，要判定为onScroll或onFling必须要建立在onDown被消费的前提下（即onDown返回true）。

来自：http://blog.csdn.net/yuyuanhuang/article/details/45068619