Android 中轴时光轴

Android 中轴时光轴

ps：好久都没有写博客了，今天正好比较空，就来写一篇，好像这才是第二篇，不过不要在意这些细节啦。

转载请注明出处：http://blog.youkuaiyun.com/qq_15736263/article/details/51941066

效果图

：
美女图片都是 熊（百）掌（度）找的，如果有涉及到您的权益，请及时联系我进行删除。
就是这样的效果，这张图片因为某些原因，已经经过ps修改，请见谅我ps功底差！
第二个Item因为需要，固定添加了paddingTop。

一些说明

刚开始在网上找这种效果的实现，也在论坛上提过问。都没有能解决问题。
其实瀑布流是很好实现的。主要是中间圆点让人十分蛋疼。

最开始有考虑过几种解决方式

使用网络上开源的瀑布流控件，然后进行重写：

发现都是用使用GridView或者是ListView或者ViewGroup实现的，使用的都是类似LinnearLayout的布局方式，修改起来比较困难，牵扯面较多，然后放弃了。

使用RecyclerView然后自定义LayoutManager：

其实这个是最好的实现方式，但是因为时间太赶，加上网络上相关资源太少。只好去参考官方StaggeredGridLayoutManager了。
然后就源码旅游了。

@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
    onLayoutChildren(recycler, state, true);
} 

private void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state,
        boolean shouldCheckForGaps) {
    final AnchorInfo anchorInfo = mAnchorInfo;
    anchorInfo.reset();

    if (mPendingSavedState != null || mPendingScrollPosition != NO_POSITION) {
        if (state.getItemCount() == 0) {
            removeAndRecycleAllViews(recycler);
            return;
        }
    }

    if (mPendingSavedState != null) {
        applyPendingSavedState(anchorInfo);
    } else {
        resolveShouldLayoutReverse();
        anchorInfo.mLayoutFromEnd = mShouldReverseLayout;
    }

    updateAnchorInfoForLayout(state, anchorInfo);

    if (mPendingSavedState == null) {
        if (anchorInfo.mLayoutFromEnd != mLastLayoutFromEnd ||
                isLayoutRTL() != mLastLayoutRTL) {
            mLazySpanLookup.clear();
            anchorInfo.mInvalidateOffsets = true;
        }
    }

    if (getChildCount() > 0 && (mPendingSavedState == null ||
            mPendingSavedState.mSpanOffsetsSize < 1)) {
        if (anchorInfo.mInvalidateOffsets) {
            for (int i = 0; i < mSpanCount; i++) {
                // Scroll to position is set, clear.
                mSpans[i].clear();
                if (anchorInfo.mOffset != INVALID_OFFSET) {
                    mSpans[i].setLine(anchorInfo.mOffset);
                }
            }
        } else {
            for (int i = 0; i < mSpanCount; i++) {
                mSpans[i].cacheReferenceLineAndClear(mShouldReverseLayout, anchorInfo.mOffset);
            }
        }
    }
    detachAndScrapAttachedViews(recycler);
    mLayoutState.mRecycle = false;
    mLaidOutInvalidFullSpan = false;
    updateMeasureSpecs(mSecondaryOrientation.getTotalSpace());
    updateLayoutState(anchorInfo.mPosition, state);
    if (anchorInfo.mLayoutFromEnd) {
        // Layout start.
        setLayoutStateDirection(LAYOUT_START);
        fill(recycler, mLayoutState, state);
        // Layout end.
        setLayoutStateDirection(LAYOUT_END);
        mLayoutState.mCurrentPosition = anchorInfo.mPosition + mLayoutState.mItemDirection;
        fill(recycler, mLayoutState, state);
    } else {
        // Layout end.
        setLayoutStateDirection(LAYOUT_END);
        fill(recycler, mLayoutState, state);
        // Layout start.
        setLayoutStateDirection(LAYOUT_START);
        mLayoutState.mCurrentPosition = anchorInfo.mPosition + mLayoutState.mItemDirection;
        fill(recycler, mLayoutState, state);
    }

    repositionToWrapContentIfNecessary();

    if (getChildCount() > 0) {
        if (mShouldReverseLayout) {
            fixEndGap(recycler, state, true);
            fixStartGap(recycler, state, false);
        } else {
            fixStartGap(recycler, state, true);
            fixEndGap(recycler, state, false);
        }
    }
    boolean hasGaps = false;
    if (shouldCheckForGaps && !state.isPreLayout()) {
        final boolean needToCheckForGaps = mGapStrategy != GAP_HANDLING_NONE
                && getChildCount() > 0
                && (mLaidOutInvalidFullSpan || hasGapsToFix() != null);
        if (needToCheckForGaps) {
            removeCallbacks(mCheckForGapsRunnable);
            if (checkForGaps()) {
                hasGaps = true;
            }