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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。
1 mItemCount = mAdapter == null ? 0 : mAdapter.getCount(); 2 final int count = mItemCount; 3 if (count > 0) { 4 final View child = obtainView(0, mIsScrap); 5 6 AbsListView.LayoutParams p = (AbsListView.LayoutParams) child.getLayoutParams(); 7 if (p == null) { 8 p = (AbsListView.LayoutParams) generateDefaultLayoutParams(); 9 child.setLayoutParams(p); 10 } 11 p.viewType = mAdapter.getItemViewType(0); 12 p.forceAdd = true; 13 14 int childHeightSpec = getChildMeasureSpec( 15 MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED), 0, p.height); 16 int childWidthSpec = getChildMeasureSpec( 17 MeasureSpec.makeMeasureSpec(mColumnWidth, MeasureSpec.EXACTLY), 0, p.width); 18 child.measure(childWidthSpec, childHeightSpec); 19 20 childHeight = child.getMeasuredHeight(); 21 childState = combineMeasuredStates(childState, child.getMeasuredState()); 22 23 if (mRecycler.shouldRecycleViewType(p.viewType)) { 24 mRecycler.addScrapView(child, -1); 25 } 26 } 27 28 if (heightMode == MeasureSpec.UNSPECIFIED) { 29 heightSize = mListPadding.top + mListPadding.bottom + childHeight + 30 getVerticalFadingEdgeLength() * 2; 31 } 32 33 if (heightMode == MeasureSpec.AT_MOST) { 34 int ourSize = mListPadding.top + mListPadding.bottom; 35 36 final int numColumns = mNumColumns; 37 for (int i = 0; i < count; i += numColumns) { 38 ourSize += childHeight; 39 if (i + numColumns < count) { 40 ourSize += mVerticalSpacing; 41 } 42 if (ourSize >= heightSize) { 43 ourSize = heightSize; 44 break; 45 } 46 } 47 heightSize = ourSize; 48 }
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。
1 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。
1 heightMeasureSpec = MeasureSpec.makeMeasureSpec(1000000, MeasureSpec.AT_MOST);
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原文地址：http://www.cnblogs.com/zyfa/p/4568709.html
