RecyclerView 加入一个滑动控件bug处理 GridView只显示第一行

如果RecyclerView 多样式布局，比如要加入一个展示多个图看的需求。自然想到用gridview给嵌套一下。

想法当然是可以的，但是发现，嵌套出来的效果是，gridview只显示一行。

想想原因 应该是给的高度不够，自然，计算高度肯定要从onMeasure入手。

看下onMeasure计算过程。

specMode中决定的，specMode一共有三种可能：

MeasureSpec.EXACTLY：父视图希望子视图的大小应该是specSize中指定的。

MeasureSpec.AT_MOST：子视图的大小最多是specSize中指定的值，也就是说不建议子视图的大小超过specSize中给定的值。

MeasureSpec.UNSPECIFIED：我们可以随意指定视图的大小。

那么，gridview的父节点是RecyclerView 自然他本身高度就是不确定的。

我们再看一下源码

 @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // Sets up mListPadding
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);

        if (widthMode == MeasureSpec.UNSPECIFIED) {
            if (mColumnWidth > 0) {
                widthSize = mColumnWidth + mListPadding.left + mListPadding.right;
            } else {
                widthSize = mListPadding.left + mListPadding.right;
            }
            widthSize += getVerticalScrollbarWidth();
        }
        
        int childWidth = widthSize - mListPadding.left - mListPadding.right;
        boolean didNotInitiallyFit = determineColumns(childWidth);

        int childHeight = 0;
        int childState = 0;

        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.isEnabled = mAdapter.isEnabled(0);
            p.forceAdd = true;

            int childHeightSpec = getChildMeasureSpec(
                    MeasureSpec.makeSafeMeasureSpec(MeasureSpec.getSize(heightMeasureSpec),
                            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;
        }

        if (widthMode == MeasureSpec.AT_MOST && mRequestedNumColumns != AUTO_FIT) {
            int ourSize = (mRequestedNumColumns*mColumnWidth)
                    + ((mRequestedNumColumns-1)*mHorizontalSpacing)
                    + mListPadding.left + mListPadding.right;
            if (ourSize > widthSize || didNotInitiallyFit) {
                widthSize |= MEASURED_STATE_TOO_SMALL;
            }
        }

        setMeasuredDimension(widthSize, heightSize);
        mWidthMeasureSpec = widthMeasureSpec;
    }

看代码我们很容知道需要这个

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) {
　　　　　　　//累加垂直高度。
            ourSize += mVerticalSpacing;
        }
        if (ourSize >= heightSize) {
            ourSize = heightSize;
            break;
        }
    }
    heightSize = ourSize;
}

因此我们可以重写gridView的onMeseaure方法
告诉父类我们要用AT_MOST模式去计算高度。

int expandSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2, MeasureSpec.AT_MOST);
super.onMeasure(widthMeasureSpec, expandSpec);
结果如图：