Android Canvas绘制的简单使用

创建一个dorw类继承View，实现构造函数和onDraw方法:

public class dorw extends View {
    /**
     * @param context
     */
    public dorw(Context context) {
        super(context);
    }

    /**
     * 在画布上绘制视图
     *
     * @param canvas
     */
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 在画布上绘制圆形
        Paint paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画笔颜色
        paint.setColor(0xffff0000);
        //设置画笔模式为填充
        paint.setStyle(Paint.Style.STROKE);
        //设置画笔宽度
        paint.setStrokeWidth(5);
        //TODO:绘制圆形
        canvas.drawCircle(this.getWidth() >> 1, this.getHeight() >> 1, this.getWidth() >> 1, paint);
        //TODO:绘制一个圆点
        paint.setAntiAlias(true);
        paint.setColor(0xff000000);
        paint.setStrokeWidth(10);
        canvas.drawPoint(this.getWidth() >> 1, this.getHeight() >> 1, paint);
        //TODO:绘制一个十字架
        paint.setAntiAlias(true);
        paint.setColor(0xff000000);
        paint.setStrokeWidth(5);
        canvas.drawLine(this.getWidth() >> 1, 0, this.getWidth() >> 1, this.getHeight(), paint);
        canvas.drawLine(0, this.getHeight() >> 1, this.getWidth(), this.getHeight() >> 1, paint);

    }
}

实例化dorw类，然后查找组件，把dorw类的对象加入到组件里面：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //TODO:获取LinearLayout实例
        LinearLayout linearLayout = findViewById(R.id.line1);
        //TODO:创建一个dorw类的对象
        View v = new dorw(this);
        //TODO:将dorw类的对象添加到linearLayout中
        linearLayout.addView(v);
    }
}

xml布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:gravity="center"
    android:orientation="vertical"
    tools:context=".MainActivity">


    <LinearLayout
        android:id="@+id/line1"
        android:layout_width="30dp"
        android:layout_height="30dp"
        android:orientation="vertical"
        android:padding="2dp" />

</LinearLayout>

效果图：