android自定义控件padding属性无效的解决

在自定义控件时，很多童鞋发现在XML布局中写上padding属性却不起作用，而且wrap_content和march_parent显示效果一样，这就需要我们在代码中对自定义View宽高做相应的改动，以自定义一个简单的圆示例，如下图（加了padding属性）：

代码如下：

    public class CircleView extends View {
    private Paint mPaint;

    public CircleView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView();
    }

    public CircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public CircleView(Context context) {
        super(context);
        initView();
    }

    private void initView() {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(8);
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // TODO Auto-generated method stub
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //对宽高的测量
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        if (widthMode==MeasureSpec.AT_MOST&&heightMode==MeasureSpec.AT_MOST) {
            setMeasuredDimension(300, 100);
        }else if (widthMode == MeasureSpec.AT_MOST) {
            setMeasuredDimension(300, heightSize);
        }else if (heightMode ==MeasureSpec.AT_MOST) {
            setMeasuredDimension(widthSize, 100);
        }
    }
    @Override
    protected void onDraw(Canvas canvas) {
        // TODO Auto-generated method stub
        super.onDraw(canvas);
        int paddingBottom = getPaddingBottom();
        int paddingLeft = getPaddingLeft();
        int paddingRight = getPaddingRight();
        int paddingTop = getPaddingTop();
        //主要是考虑到VIEW周围的空白
        int width = getWidth()-paddingLeft-paddingRight;
        int height = getHeight()-paddingTop-paddingBottom;
        int radius = Math.min(width, height)/2;
        canvas.drawCircle(paddingLeft+width/2, paddingTop+height/2, radius, mPaint);
    }
}

circle.xml布局代码如下：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffff"
    android:orientation="vertical" >

    <com.example.customview.CircleView
        android:layout_width="wrap_content"
        android:layout_height="100dp"
        android:layout_margin="20dp"
        android:background="#000000"
        android:padding="20dp" />

LinearLayout>

关于自定义view，可以参考《android开发艺术探索》《android群英传》一书，