RecycerView getChildCount（）和getItemCount（）返回相同的值

Question

RecycerView有一个InfiniteScrollListener，在该侦听器中，在onscrolled()方法中，我计算可见项计数和总计项计数，以检查是否应该加载新项。当totalItemCount和visibleItemCount相同时，会导致无限循环的加载。侦听器与我的另一个RecycerViewCoordinatorLayout或NestedScrollView作为父级的侦听器一起工作得很好。我想保持这种结构，因为客户不会接受改变。

我在一个活动中有一个片段，它的布局如下所示

CoordinatorLayout{
 NestedScrollView{
    RecyclerView{
    }
 }
}

compileSdkVersion 24
buildToolsVersion "23.0.3"
...
minSdkVersion 21
targetSdkVersion 24

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/app_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay"
        app:layout_behavior="com.paxotic.paxira.util.behavior.AppBarFlingBehavior">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/toolbar_layout"
            android:layout_width="match_parent"
            android:layout_height="@dimen/app_bar_height_small"
            app:contentScrim="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|exitUntilCollapsed">

            <RelativeLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:background="#000000"
                app:layout_collapseMode="parallax">

                <ImageView
                    android:id="@+id/img_background"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:alpha="0.5"
                    android:scaleType="centerCrop"
                    tools:src="@drawable/bg_greeting_activity" />

            </RelativeLayout>

        </android.support.design.widget.CollapsingToolbarLayout>

    </android.support.design.widget.AppBarLayout>

    <include
        layout="@layout/activity_profile_content"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

    <android.support.design.widget.FloatingActionButton
       ... />

</android.support.design.widget.CoordinatorLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.NestedScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior">

    ...

    <android.support.v7.widget.RecyclerView
        android:id="@+id/feedRecycler"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        android:paddingBottom="@dimen/spacing_normal"
        tools:listitem="@layout/list_item_activity" />

    ...

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

private void init() {

    feedAdapter = new FeedAdapter(host);
    feedAdapter.setHasStableIds(true);

    LinearLayoutManager layoutManager = new LinearLayoutManager(host);
    feedRecycler.setLayoutManager(layoutManager);
    feedRecycler.setNestedScrollingEnabled(false);
    feedRecycler.setHasFixedSize(true);
    feedRecycler.setAdapter(feedAdapter);

    infiniteScrollListener = new InfiniteScrollListener(host, layoutManager) {
        @Override
        public void onLoadMore(int pageIndex) {
            if (!feedAdapter.isLoading) {
                loadFeed(pageIndex);
            }
        }
    };
    feedRecycler.addOnScrollListener(infiniteScrollListener);
}

public abstract class InfiniteScrollListener extends RecyclerView.OnScrollListener {
    private int previousTotal = 0; // The total number of items in the dataset after the last load
    private boolean loading = false; // True if we are still waiting for the last set of data to load.
    private static final int VISIBLE_THRESHOLD = 5; // The minimum amount of items to have below your current scroll position before loading more.
    int firstVisibleItem, visibleItemCount, totalItemCount;

    private int current_page = 0;
    private int loadingItemCount;

    private LinearLayoutManager mLinearLayoutManager;

    public InfiniteScrollListener(Context context, LinearLayoutManager linearLayoutManager) {
        this.mLinearLayoutManager = linearLayoutManager;
        loadingItemCount = context.getResources().getInteger(R.integer.feed_pull_item_count);
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);

        if (dy < 0) return;        // check for scroll down

        visibleItemCount = mLinearLayoutManager.getChildCount();
        totalItemCount = mLinearLayoutManager.getItemCount();
        firstVisibleItem = mLinearLayoutManager.findFirstVisibleItemPosition();

        synchronized (this) {

            if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + VISIBLE_THRESHOLD)) {
                // End has been reached, Do something
                current_page++;
                onLoadMore(current_page);
                loading = true;
            }
        }
    }

    public abstract void onLoadMore(int current_page);

    public void setLoading(boolean loading) {
        this.loading = loading;
    }

    @Override
    public void onScrollStateChanged(RecyclerView view, int scrollState) {
        // Don't take any action on changed
    }
}

Answer 1

你得到了真正的视图数。如果adapter有15个项，并且（（LinearLayoutManager）MyRecyerView.getLayoutManager（））.getChildCount（）返回7个项，则视图中有两个项可见，因为在更新新项直到保持相同的高度后，最大高度值或静态高度值。

模型（适配器）中项的计数和视图的计数不是一回事。

RecycerView并没有保存内存中所有15项的视图，在您的情况下，它只有7项。当你滚动时，它重用这7个视图来显示不同的项目。这样做的目的是提高呈现性能。