android 事件分发机制2-案例测试

我们来看程序的代码：

要求：

1.通过手指移动来拖动图片

2.控制图片不能超出屏幕显示区域

技术点:

1.MotionEvent处理

2.对View进行动态定位(layout)

package im.weiyuan.com.viewutils;

import android.content.Intent;
import android.os.PersistableBundle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity  implements View.OnTouchListener{

    private ImageView iv_main;
    private RelativeLayout parentView;
    private int lastX;
    private int lastY;
    private int maxRight;
    private int maxBottom;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        iv_main = (ImageView) findViewById(R.id.iv_main);
        parentView = (RelativeLayout) iv_main.getParent();
  /*
  int right = parentView.getRight(); //0
  int bottom = parentView.getBottom(); //0
  Toast.makeText(this, right+"---"+bottom, 1).show();
  */
        //设置touch监听
        iv_main.setOnTouchListener(this);

    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.d("123456","activity dispatchTouchEvent is called" +ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.d("123456","activity onTouchEvent  is called"+event.getAction());
        return super.onTouchEvent(event);
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        //得到事件的坐标
        int eventX = (int) event.getRawX();
        int eventY = (int) event.getRawY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                //得到父视图的right/bottom
                if(maxRight==0) {//保证只赋一次值
                    maxRight = parentView.getRight();
                    maxBottom = parentView.getBottom();
                }
                //第一次记录lastX/lastY
                lastX =eventX;
                lastY = eventY;
                break;
            case MotionEvent.ACTION_MOVE:
                //计算事件的偏移
                int dx = eventX-lastX;
                int dy = eventY-lastY;
                //根据事件的偏移来移动imageView
                int left = iv_main.getLeft()+dx;
                int top = iv_main.getTop()+dy;
                int right = iv_main.getRight()+dx;
                int bottom = iv_main.getBottom()+dy;
                //限制left >=0
                if(left<0) {
                    right += -left;
                    left = 0;
                }
                //限制top
                if(top<0) {
                    bottom += -top;
                    top = 0;
                }
                //限制right <=maxRight
                if(right>maxRight) {
                    left -= right-maxRight;
                    right = maxRight;
                }
                //限制bottom <=maxBottom
                if(bottom>maxBottom) {
                    top -= bottom-maxBottom;
                    bottom = maxBottom;
                }
                iv_main.layout(left, top, right, bottom);
                //再次记录lastX/lastY
                lastX = eventX;
                lastY = eventY;
                break;
            default:
                break;
        }
        return true;//所有的motionEvent都交给imageView处理

    }
}

<RelativeLayout 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" >
    <ImageView
        android:id="@+id/iv_main"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@mipmap/ic_launcher"/>
</RelativeLayout>