GridView的高度自适应

接着上面一篇文章。

当GridView不知道parent高度的时候，也就是MeasureSpec是UNSPECIFIED，这个时候，GridView高度为第一个child的高度，并显示滚动条。

         mItemCount = mAdapter == null ? 0 : mAdapter.getCount();
         final int count = mItemCount;
         if (count > 0) {
             final View child = obtainView(0, mIsScrap);

             AbsListView.LayoutParams p = (AbsListView.LayoutParams) child.getLayoutParams();
             if (p == null) {
                 p = (AbsListView.LayoutParams) generateDefaultLayoutParams();
                 child.setLayoutParams(p);
             }
             p.viewType = mAdapter.getItemViewType(0);
             p.forceAdd = true;

             int childHeightSpec = getChildMeasureSpec(
                     MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED), 0, p.height);
             int childWidthSpec = getChildMeasureSpec(
                     MeasureSpec.makeMeasureSpec(mColumnWidth, MeasureSpec.EXACTLY), 0, p.width);
             child.measure(childWidthSpec, childHeightSpec);

             childHeight = child.getMeasuredHeight();
             childState = combineMeasuredStates(childState, child.getMeasuredState());

             if (mRecycler.shouldRecycleViewType(p.viewType)) {
                 mRecycler.addScrapView(child, -1);
             }
         }

         if (heightMode == MeasureSpec.UNSPECIFIED) {
             heightSize = mListPadding.top + mListPadding.bottom + childHeight +
                     getVerticalFadingEdgeLength() * 2;
         }

         if (heightMode == MeasureSpec.AT_MOST) {
             int ourSize =  mListPadding.top + mListPadding.bottom;

             final int numColumns = mNumColumns;
             for (int i = 0; i < count; i += numColumns) {
                 ourSize += childHeight;
                 if (i + numColumns < count) {
                     ourSize += mVerticalSpacing;
                 }
                 if (ourSize >= heightSize) {
                     ourSize = heightSize;
                     break;
                 }
             }
             heightSize = ourSize;
         }

我们可以发现，确实是只设置为第一个child的高度，当MeasureSpec是AT_MOST的时候，才会读取所有child的高度。

再网上，搜到了下面的办法。

heightMeasureSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE, MeasureSpec.AT_MOST);

其实这是不对的，MeasureSpec的前两个bits是mode，size的大小不能超过30位。于是，稍微修改，size设置为1000000，应该是足够了，当不足够的时候，你的app如果还没更新早就该被淘汰了。

heightMeasureSpec = MeasureSpec.makeMeasureSpec(1000000, MeasureSpec.AT_MOST);