GridView的高度自适应

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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;

         }