仿淘宝京东商品规格属性选择的最简单实现

商城里面的规格选择，网上大部分是自定义控件实现的，显得很是麻烦，而我的实现方式是大家最常用的控件RecyclerView，特点是性能好，简单。废话不多说，先看实现的效果图： 上图效果的实现主要是 RecyclerView和flowlayout（流式布局）.

RecyclerView设置最大高度

如图规格多的时候，RecyclerView要有个最大高度，我们设置 android:maxHeight="300dp"是没有效果的，因为RecyclerView没有maxHigh这个属性，那怎么实现这个效果呢？通过查看源码，

@Override
protected void onMeasure(int widthSpec, int heightSpec) {
...
if (mLayout.mAutoMeasure) {
    ...
    // now we can get the width and height from the children.
    mLayout.setMeasuredDimensionFromChildren(widthSpec, heightSpec);
    if (mLayout.shouldMeasureTwice()) {
        ...        
        // now we can get the width and height from the children.
        mLayout.setMeasuredDimensionFromChildren(widthSpec, heightSpec);
    }
} else {
  ...
}
}

当RecyclerView的LayoutManager#isAutoMeasureEnabled()返回true时，RecyclerView高度取决于children view的布局高度，并非取决于RecyclerView自身的测量高度。

下面是setMeasuredDimensionFromChildren(int widthSpec, int heightSpec)源码

 void setMeasuredDimensionFromChildren(int widthSpec, int heightSpec) {
final int count = getChildCount();
if (count == 0) {
    mRecyclerView.defaultOnMeasure(widthSpec, heightSpec);
    return;
}
int minX = Integer.MAX_VALUE;
int minY = Integer.MAX_VALUE;
int maxX = Integer.MIN_VALUE;
int maxY = Integer.MIN_VALUE;
for (int i = 0; i < count; i++) {
    View child = getChildAt(i);
    final Rect bounds = mRecyclerView.mTempRect;
    getDecoratedBoundsWithMargins(child, bounds);
    if (bounds.left < minX) {
        minX = bounds.left;
    }
    if (bounds.right > maxX) {
        maxX = bounds.right;
    }
    if (bounds.top < minY) {
        minY = bounds.top;
    }
    if (bounds.bottom > maxY) {
        maxY = bounds.bottom;
    }
}
mRecyclerView.mTempRect.set(minX, minY, maxX, maxY);
setMeasuredDimension(mRecyclerView.mTempRect, widthSpec, heightSpec);
}

该方法计算了RecyclerView当前所有Child View的布局范围mRecyclerView.mTempRect，最后调用了public void setMeasuredDimension(Rect childrenBounds, int wSpec, int hSpec)，并将得出的布局范围mRecyclerView.mTempRect、RecyclerView的测量参数widthSpec、heightSpec作为参数传入，以此来决定RecyclerView最终宽高值。

最终解决方法

因此，我们只需要重写LayoutManager的public void setMeasuredDimension(Rect childrenBounds, int wSpec, int hSpec)方法即可为RecyclerView设置最大宽高。

` @Override
public void setMeasuredDimension(Rect childrenBounds, int wSpec, int hSpec) {
    super.setMeasuredDimension(childrenBounds, wSpec, View.MeasureSpec.makeMeasureSpec(DeviceUtil.dp2px(mContext,246), AT_MOST));
}`

属性的标签实现

标签的实现用的是flowlayout，用法很简单，这里就不在描述了。

至此，如图的效果就实现了，还有不懂的可看demo代码。

查看源码