安卓之单点和多点触摸（画圆）

1.知识图谱

A.单点触摸

自己写一个MyView实体类继承view

代码如下：

public class MyView extends View {

    private float x;
    private float y;
    private int r=100;


    public MyView(Context context) {
        super(context);
    }

    public MyView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint=new Paint();
        canvas.drawCircle(x,y,r,paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //获取手指的行为
        int action=event.getAction();
        //获取手指的坐标
        x=event.getX();
        y=event.getY();

        switch (action) {
            case MotionEvent.ACTION_DOWN:
                break;
            case MotionEvent.ACTION_UP:
                
                break;
            case MotionEvent.ACTION_MOVE:
                break;
        }
        //重新调用onDraw   重绘
        invalidate();
        return true;
    }
}

2.多点触摸

首先要写一个Circle的实体类

package com.example.cookie.android0709twopointstouch;

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;

import java.util.Random;

/**
 * Created by Administrator on 2017/7/9 0009.
 */

public class Circle {
    public float x;
    public float y;
    public int r=100;
    public int pointId;

    public int red;
    public int green;
    public int blue;
    Random random=new Random();


    public Circle(float x, float y, int pointId) {
        this.x = x;
        this.y = y;
        this.pointId = pointId;
        red=random.nextInt(255);
        green=random.nextInt(255);
        blue=random.nextInt(255);

    }
    public void drawSelf(Canvas canvas, Paint paint){
        //设置随机画笔的颜色
        paint.setColor(Color.rgb(red,green,blue));
        paint.setStyle(Paint.Style.STROKE);
        canvas.drawCircle(x,y,r,paint);
    }
}

再写一个MyView继承View

package com.example.cookie.android0709twopointstouch;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Administrator on 2017/7/9 0009.
 */

public class MyView extends View {

    public List<Circle> circles=new ArrayList<>();

    public MyView(Context context) {
        super(context);
    }

    public MyView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint=new Paint();
        for (Circle circle : circles) {
            circle.drawSelf(canvas,paint);
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        //获取手指的行为
        int action=event.getAction();
        int action_code=action&0xff;
        //手指的下标
        int pointIndex=action>>8;
        //获取手指的下标
        float x=event.getX(pointIndex);
        float y=event.getY(pointIndex);
        //获取手指的名字ID
        int pointId=event.getPointerId(pointIndex);
        if (action_code>=5){
            action_code-=5;
        }
        switch (action_code) {
            case MotionEvent.ACTION_DOWN:
                //实例化圆
                Circle circle=new Circle(x,y,pointId);
                circles.add(circle);
                break;
            case MotionEvent.ACTION_UP:
                circles.remove(get(pointId));
                break;
            case MotionEvent.ACTION_MOVE:
                for (int i = 0; i < event.getPointerCount(); i++) {
                   int id=event.getPointerId(i);
                    get(id).x=event.getX();
                    get(id).y=event.getY();
                }
                break;
        }

        //重新绘制
        invalidate();

        return true;
    }

    public Circle get(int pointId){
        for (Circle circle : circles) {
            if (circle.pointId==pointId){
                return circle;
            }
        }
        return null;
    }
}