随机获取四位数+TextView

1.布局

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.bw.ymy.demo7.Custorm
        android:id="@+id/custorm"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="40sp"

        />
</android.support.constraint.ConstraintLayout>

2.TextView

package com.bw.ymy.demo7;

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

public class Custorm extends android.support.v7.widget.AppCompatTextView{

    Paint paint;
    int i=0;
    public Custorm(Context context) {
        super(context);
        init();
    }



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

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
    }
    private void changeText() {

        setText(String.valueOf(getNums()));

        if(i%2==0){
            setBackgroundColor(Color.YELLOW);
        }else{
            setBackgroundColor(Color.RED);
        }
        i++;

    }


    private int getNums() {
        //获取随机数Math.random()，取值范围[0, 1);
        //所有*9000后取值范围 [0, 9000)
        //最后加上1000，范围[1000, 10000)
        return (int) (Math.random()*9000+1000);
    }



    private void init() {
        changeText();
        setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                changeText();
            }
        });
    }
}

3.主页面不用写!