1、自定義一個類繼承View

package com.gj.gejuan20181130;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.os.Build;
import android.support.annotation.RequiresApi;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class BallView extends View {

private Paint mCirclePaint;
private int x=100;
private int y=100;


public BallView(Context context) {
    super(context);
    init();
}

public BallView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
}

public BallView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();
}

@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
public BallView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
    init();
}

private void init() {
    mCirclePaint = new Paint();//建立畫筆
    mCirclePaint.setStyle(Paint.Style.FILL);//設定樣式
    mCirclePaint.setColor(Color.GREEN);//設定顏色
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.drawCircle(x,y,100,mCirclePaint);//畫圓 第一個引數x軸，第二個引數y，軸座標，第三個引數半徑,第四個引數畫筆
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    x = (int) event.getX();//獲得X座標
    y = (int) event.getY();//獲得y座標
    invalidate();//重新整理
    return true;//攔截處理
}
 

}

注意：
build一下然後在main佈局中引用自定義view