Android 自定义View，并绘制简单图形

        新建MyView类，继承View。添加两个参数的构造方法，并覆写onDraw()方法 new一个Paint 画笔对象。在onDraw()方法中画图。paint是画笔，canvas是画布。

package com.engineer.shizhibin.drawpicture;
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;

/**
 * 1.覆写onDraw()
 * 2.初始化画笔
 * 3.canvas 画板
 * Created by 13922 on 2018/6/2.
 */

public class MyView extends View {
    private Paint mPaint = new Paint();
    public MyView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawLine(100,100,300,100,mPaint);
        mPaint.setColor(Color.BLUE);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(20);
        canvas.drawCircle(290,250,180,mPaint);
        mPaint.setColor(Color.YELLOW);
        canvas.drawCircle(480,430,180,mPaint);
        mPaint.setColor(Color.BLACK);
        canvas.drawCircle(670,250,180,mPaint);
        mPaint.setColor(Color.GREEN);
        canvas.drawCircle(860,430,180,mPaint);
        mPaint.setColor(Color.RED);
        canvas.drawCircle(1050,250,180,mPaint);
        mPaint.setTextSize(100);
        canvas.drawText("北京欢迎你",600,1000,mPaint);

    }
}

        在Activity_Main.xml中添加刚才自定义的View，设置属性。一定要用类全名。

<com.engineer.shizhibin.drawpicture.MyView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#0ff" />

        画图结果：