@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // 獲取寬度的Size和Mode
    int widthSize = MeasureSpec.getSize(widthMeasureSpec);
    int widthMode = MeasureSpec.getMode(widthMeasureSpec);
    // 如果Mode是精確的，直接返回
    if (widthMode == MeasureSpec.EXACTLY) {
        setMeasuredDimension(widthSize, heightMeasureSpec);
        return;
    }
    // 計(jì)算View的寬度
    int desiredWidth = getPaddingLeft() + getPaddingRight() + defaultWidth;
    int measuredWidth;
    if (desiredWidth < widthSize) {
        measuredWidth = desiredWidth;
    } else {
        measuredWidth = widthSize;
    }
    // 設(shè)置寬度和高度的Size和Mode
    int heightSize = MeasureSpec.getSize(heightMeasureSpec);
    int heightMode = MeasureSpec.getMode(heightMeasureSpec);
    int measuredHeight = defaultHeight;
    if (heightMode == MeasureSpec.EXACTLY) {
        measuredHeight = heightSize;
    } else if (heightMode == MeasureSpec.AT_MOST) {
        measuredHeight = Math.min(defaultHeight, heightSize);
    }
    setMeasuredDimension(measuredWidth, measuredHeight);
}

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
    int count = getChildCount();
    int left = getPaddingLeft();
    int top = getPaddingTop();
    int right = getMeasuredWidth() - getPaddingRight();
    int bottom = getMeasuredHeight() - getPaddingBottom();
    for (int i = 0; i < count; i++) {
        View child = getChildAt(i);
        if (child.getVisibility() == GONE) {
            continue;
        }
        LayoutParams lp = (LayoutParams) child.getLayoutParams();
        int childLeft = left + lp.leftMargin;
        int childTop = top + lp.topMargin;
        int childRight = right - lp.rightMargin;
        int childBottom = bottom - lp.bottomMargin;
        child.layout(childLeft, childTop, childRight, childBottom);
    }
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    //繪制文本
    String text = "Hello World";
    Paint paint = new Paint();
    paint.setTextSize(50);
    paint.setColor(Color.RED);
    paint.setAntiAlias(true);
    canvas.drawText(text, 0, getHeight() / 2, paint);
}

public class MyViewGroup extends ViewGroup {
    public MyViewGroup(Context context) {
        super(context);
    }
    public MyViewGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // 測(cè)量子View的寬高
        measureChildren(widthMeasureSpec, heightMeasureSpec);
        // 獲取ViewGroup的寬高大小
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        // 設(shè)置ViewGroup的寬高
        setMeasuredDimension(widthSize, heightSize);
    }
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        // 遍歷所有子View，設(shè)置它們的位置和大小
        int childCount = getChildCount();
        int left, top, right, bottom;
        for (int i = 0; i < childCount; i++) {
            View childView = getChildAt(i);
            left = childView.getLeft();
            top = childView.getTop();
            right = childView.getRight();
            bottom = childView.getBottom();
            childView.layout(left, top, right, bottom);
        }
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 畫背景
        canvas.drawColor(Color.WHITE);
    }
    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        // 繪制每個(gè)子View的內(nèi)容
        for (int i = 0; i < getChildCount(); i++) {
            View childView = getChildAt(i);
            childView.draw(canvas);
        }
    }
}