自定義控件

package com.qianqian.day4;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button btn = new Button(this);

        findViewById(R.id.cv).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
//                ((CustemView)v).setPaint();
                Toast.makeText(MainActivity.this, "dddd", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

package com.qianqian.day4;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import java.util.Random;

/**
 * 作用：測量方法
 * 擺放的位置--在自定義viewgroup的時候需要使用
 * 用來繪製
 * 作者：李倩 on 2017/9/28 09:30
 */
public class CurrView extends View{
    Paint paint;
    char[] array=new char[4];
    Random r=new Random();
    float downX=0;
    //在類中直接使用new關鍵字實例化控件時使用的構造方法
    public CurrView(Context context) {
        super(context);
        init();
    }
//在佈局文件中創建的控件 使用的是第二個構造方法
    public CurrView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public CurrView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }
    private void init() {
        paint=new Paint();
        //抗鋸齒
        paint.setAntiAlias(true);
        paint.setColor(Color.RED);
        paint.setStrokeWidth(10);
    }
    //畫布
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
     /*   //直線
        canvas.drawLine(0,0,100,100,paint);
        //圓，空心圓
        paint.setColor(Color.RED);
        paint.setStyle(Paint.Style.STROKE);
        canvas.drawCircle(100,100,50,paint);
        //加載圖片
        Bitmap bit= BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher);
        canvas.drawBitmap(bit,100,100,paint);*/
        for (int i = 0; i <4 ; i++) {
            String a=r.nextInt(10)+"";
            char[] temp=a.toCharArray();
            array[i]=temp[0];

        }
        canvas.drawRect(100,100,300,200,paint);
        paint.setColor(Color.YELLOW);
        paint.setTextSize(80);
        canvas.drawText(array,0,4,100,200,paint);

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()){
            case  MotionEvent.ACTION_DOWN:
                paint.setColor(Color.BLUE);
                invalidate();
                break;
            case  MotionEvent.ACTION_MOVE:
                break;
            case  MotionEvent.ACTION_UP:
                float upX=event.getX();
                if (upX>100&&upX<200) {
                    paint.setColor(Color.RED);
                    invalidate();
                }
                break;
        }
        return super.onTouchEvent(event);
    }
    public  void  setPaint(){
        paint.setColor(Color.BLACK);
        invalidate();
    }
}

<?xml version="1.0" encoding="utf-8"?>
<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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.qianqian.day4.MainActivity">

    <com.qianqian.day4.CurrView
        android:id="@+id/cv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
         />
</RelativeLayout>