android自定义控件--学习

public class MyView extends View {
    private String TAG="MyView";
    private Paint mPaint;   //画笔
    private RectF oval;
    public MyView(Context context) {
        super(context);
        init();
    }

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

    /**
     * 初始化
     */
    private void init() {
        mPaint=new Paint();
        // 设置Paint为无锯齿
        mPaint.setAntiAlias(true);
        oval=new RectF();
    }

    //测量
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int widthMode=MeasureSpec.getMode(widthMeasureSpec);
        int widthSize=MeasureSpec.getSize(widthMeasureSpec);
        int heightMode=MeasureSpec.getMode(heightMeasureSpec);
        int heightSize=MeasureSpec.getSize(heightMeasureSpec);
        switch (widthMode){
            case MeasureSpec.AT_MOST:
                //子容器可以是声明大小内的任意大小.
                break;
            case MeasureSpec.EXACTLY:
                //父容器已经为子容器设置了尺寸,子容器应当服从这些边界,不论子容器想要多大的空间.
                break;
            case MeasureSpec.UNSPECIFIED:
                //父容器对于子容器没有任何限制,子容器想要多大就多大.
                break;

        }
        Log.e(TAG, "onMeasure--widthSize-->" + widthSize);
        Log.e(TAG, "onMeasure--heightMode-->" + heightMode);
        Log.e(TAG, "onMeasure--heightSize-->" + heightSize);
    }
    //画的位置
    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        Log.e(TAG, "onLayout");
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint.setColor(Color.BLUE);
        int with=getWidth();
        int height=getHeight();
        mPaint.setStyle(Paint.Style.FILL);
        // 画一个正放形 前面两个是左上角坐标 后面两个是右下角坐标
        canvas.drawRect(0,20,30,50,mPaint);

    }