自定义控件

activity_main.xml页面

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" tools:context="com.example.g160628_18_widget.MainActivity">

    <com.example.g160628_18_widget.MyButton
        android:layout_width="300dp"
        android:layout_height="300dp"
       />


</LinearLayout>

package com.example.g160628_18_widget;

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

/**
 * Created by Administrator on 2017/7/8 0008.
 */

public class MyButton extends View {

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

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

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

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

    /**
     * @param canvas 画布
     */
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawColor(Color.RED);
        //实例化路径
        Path path = new Path();
        path.moveTo(100, 100);
        path.lineTo(300, 100);
        path.lineTo(150, 300);
        path.lineTo(200, 50);
        path.lineTo(250, 300);
        path.lineTo(100, 100);
        //实例化一个画笔
        Paint paint = new Paint();
        paint.setColor(Color.GREEN);
        //画路径
        canvas.drawPath(path, paint);

    }

}