android 中怎样构建一个底部导航

在TabViewBase中主要的方法就是测量，其他的都是对接口的简单实现。

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);

// 得到绘制icon的宽
int bitmapWidth = Math.min(getMeasuredWidth() - getPaddingLeft()
- getPaddingRight(), getMeasuredHeight() - getPaddingTop()
- getPaddingBottom() - mTextBound.height());

int left = getMeasuredWidth() / 2 - bitmapWidth / 2;
int top = (getMeasuredHeight() - mTextBound.height()) / 2 - bitmapWidth / 2;
// 设置icon的绘制范围
mIconRect = new Rect(left, top, left + bitmapWidth, top + bitmapWidth);
// 设置指示点的范围
int indicatorRadius = mIndicatorSize / 2;
int tabRealHeight = bitmapWidth + mTextBound.height();
mIndicatorRect = new Rect(left + tabRealHeight* 4/5 - indicatorRadius, top, left+tabRealHeight* 4/5 + indicatorRadius, top + mIndicatorSize);
}