为什么我的StaggeredGrid RecyclerView布局每个项目,而不仅仅是可见的？

Question

我有一个包含370个项目的交错网格,带有图像.

我想确保快速回收物品以注意内存,但是创建ViewHolder然后绑定到适配器中的每个项目,并且不关注子项是否可见

我尝试了以下内容

StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);
rv.setLayoutManager(lm);

rv.setItemViewCacheSize(20); //Has no effect

RecyclerView.RecycledViewPool pool = new RecyclerView.RecycledViewPool();
pool.setMaxRecycledViews(0, 20);
rv.setRecycledViewPool(pool); //also has no effect

日志显示onCreateViewHolder和onBindViewHolder每次调用185次.然后在恢复对onCreateViewHolder的调用之前调用onViewRecycled 185次,直到我们达到完整的370.

这对我来说可能是一个理解问题,但我认为RecyclerView应该只绑定那些可见的视图,或者仅仅支持20个视图,或者20个池中的20个,但是很多适合屏幕.如何使用StaggeredGridLayoutManager实现此目的？

如果我听滚动更改并使用findFirstCompletelyVisibleItemPositions和findLastCompletelyVisibleItemPositions,这仍然跨越适配器中的每一项,而不仅仅是适合屏幕的6项

我的适配器代码

class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {

    static final int NUM_COLS = 3;
    private final LayoutInflater mInflater;
    private final List<GridItem> mEntries;
    private int mLastExpanded; //stores where the last expanded item was
    private OnCardClickListener mOnItemClick;

    MyAdapter(Context context) {
        super();
        mEntries = new ArrayList<>();
        mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    void setOnTileClickListener(@Nullable OnCardClickListener listener) {
        mOnItemClick = listener;
        notifyDataSetChanged(); //recall bind logic
    }

    void setItems(Collection<GridItem> items) {
        mEntries.clear();
        mEntries.addAll(items);
        sort();
    }

    @WorkerThread
    private void sort() {
        Collections.sort(mEntries, (thisEntry, otherEntry) -> {
            int ret;
            if (otherEntry == null || thisEntry.getCreated() == otherEntry.getCreated()) {
                ret = 0;
            } else if (thisEntry.getCreated() > otherEntry.getCreated()) {
                ret = -1;
            } else {
                ret = 1;
            }
            return ret;
        });
    }

    @Override
    public int getItemCount() {
        return mEntries.size();
    }

    private GridItem getItem(int position) {
        return mEntries.get(position);
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return new MyViewHolder(mInflater.inflate(R.layout.li_grid_item, parent, false));
    }

    @Override
    public void onViewRecycled(MyViewHolder holder) {
        super.onViewRecycled(holder);
        holder.onViewRecycled(); //clears bitmap reference
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        determineTileSize(holder, position);
        holder.bind(getItem(position),  mOnItemClick);
    }

    private void determineTileSize(MyViewHolder holder, int position) {
        ViewGroup.LayoutParams cardParams = holder.getCardLayout().getLayoutParams();
        StaggeredGridLayoutManager.LayoutParams gridItemParams = (StaggeredGridLayoutManager.LayoutParams) holder.itemView.getLayoutParams();
        if (shouldBeExpanded(position)) {
            cardParams.height = (int) holder.getCard().getResources().getDimension(R.dimen.spacing_card_large);
            mLastExpanded = position;
            gridItemParams.setFullSpan(true);
        }
        holder.getCardLayout().setLayoutParams(cardParams);
    }

    private boolean shouldBeExpanded(int position) {
        return position > (mLastExpanded + NUM_COLS);  //minimum 1 row between enlarged
    }

}

我的活动布局结构

<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" ...>
    <android.support.design.widget.AppBarLayout ...>
        <android.support.design.widget.CollapsingToolbarLayout ...>
            <android.support.v7.widget.Toolbar
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin" ... />
            <android.support.design.widget.TabLayout ...
                app:layout_collapseMode="pin"
                android:layout_width="wrap_content"
                android:layout_height="?attr/actionBarSize" />
        </android.support.design.widget.CollapsingToolbarLayout>
    </android.support.design.widget.AppBarLayout>
    <FrameLayout
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
    <FrameLayout
        android:id="@+id/bottom_sheet"
        android:layout_width="match_parent"
        android:layout_height="@dimen/height_backdrop"
        android:minHeight="@dimen/height_backdrop"
        android:background="@color/colorAccent"
        android:visibility="gone"
        app:elevation="@dimen/spacing_narrow"
        app:behavior_peekHeight="0dp"
        app:behavior_hideable="true"
        app:layout_behavior="android.support.design.widget.BottomSheetBehavior" />
</android.support.design.widget.CoordinatorLayout>

片段布局

<android.support.v4.widget.NestedScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior" ...>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.v7.widget.RecyclerView
            android:id="@+id/grid_recycler_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical" />

            <!-- Empty and loading views -->

    </RelativeLayout>

</android.support.v4.widget.NestedScrollView>

Answer 1

问题:

你面临这个问题的原因是因为你已经加入RecyclerView了NestedScrollView.

原因:

这不是我第一次听说这个问题,我和可能每个试图投入RecyclerView的人NestedScrollView都面临这个问题(如果注意到的话).

据我所知,原因是因为当你放入RecyclerView时NestedScrollView,它无法确定所需的确切高度RecyclerView.通常,开发人员为此假设(简单来说),一旦上面的所有视图都离开了屏幕,RecyclerView的高度应该是match_parent.但不幸的是,事实并非如此.

它RecyclerView以某种方式使wrap_content添加其所有视图,然后测量其高度(如果我错了,请纠正我).不知道一个可能的错误或预期的行为,但我相信NestedScrollView应该能够明确地处理这种情况,否则,将RecyclerView在NestedScrollView完全是无用的,因为它没有回收的意见,彻底摧毁了RecyclerView概念,从而消耗大量的内存.

临时解决方案:

只需删除RecyclerViewfrom NestedScrollView即可正确重用视图.

注意:答案可能不是100%正确,因为它完全基于我的个人观察和经验.任何更好的解决方案或答案的改进表示赞赏.