VelocityTracker检测手指的移动速度

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="sowell.oracle.com.view.MainActivity">
        <!--
        tv用于显示手指移动的速度
    -->
    <TextView
        android:id="@+id/tv"
        android:text="aaa"
        android:layout_width="100dp"
        android:layout_height="match_parent" />
</LinearLayout>

MainActivity.java

package sowell.oracle.com.view;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    public VelocityTracker velocityTracker;
    public TextView tv;
    public double xVelocity;
    public double yVelocity;

    public void init(){
        tv=(TextView)findViewById(R.id.tv);
        velocityTracker=VelocityTracker.obtain();
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
        tv.setText("bbb");
    }


    //重写点击事件的回调函数
    @Override
    public boolean onTouchEvent(MotionEvent event) {

        final int action =event.getAction();
        velocityTracker=VelocityTracker.obtain();
        velocityTracker.addMovement(event);


        switch (action){
            case MotionEvent.ACTION_MOVE:
                velocityTracker.computeCurrentVelocity(1000);   //计算每1000ms手指移动的像素
                xVelocity=velocityTracker.getXVelocity();
                yVelocity=velocityTracker.getYVelocity();
                add(xVelocity,yVelocity);
                break;

            case MotionEvent.ACTION_UP:
                velocityTracker.clear();                        //回收VelocityTracker
                velocityTracker.recycle();
                break;

            case MotionEvent.ACTION_CANCEL:
                velocityTracker.clear();
                velocityTracker.recycle();
                break;

        }

        return super.onTouchEvent(event);
    }





    void add(double x,double y)
    {
        final String info=String.format("水平速度：%f
竖直速度：%f",x,y);
        tv.setText(info);
    }
}