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。

 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);