请问,如何获取到RecyclerView中每个item在屏幕上显示的时长

Question

有个需求,要能获取到RecyclerView中每个item在屏幕上显示的时长,哪位大神知道

Answer 1

只要找到View（ViewHolder）显示隐藏的调用函数，就能计算出每个View（ViewHolder）的显示时长。

很幸运的时，RecyclerView提供了这样的接口函数，而且还是两对接口函数：

1.RecyclerView#Adapter提供了一对函数：onViewAttachedToWindow(VH)和onViewDetachedFromWindow(VH)

public abstract static class Adapter<VH extends ViewHolder> {
    ... ...
    
    /**
     * Called when a view created by this adapter has been attached to a window.
     *
     * <p>This can be used as a reasonable signal that the view is about to be seen
     * by the user. If the adapter previously freed any resources in
     * {@link #onViewDetachedFromWindow(RecyclerView.ViewHolder) onViewDetachedFromWindow}
     * those resources should be restored here.</p>
     *
     * @param holder Holder of the view being attached
     */
    public void onViewAttachedToWindow(VH holder) {
    }

    /**
     * Called when a view created by this adapter has been detached from its window.
     *
     * <p>Becoming detached from the window is not necessarily a permanent condition;
     * the consumer of an Adapter's views may choose to cache views offscreen while they
     * are not visible, attaching and detaching them as appropriate.</p>
     *
     * @param holder Holder of the view being detached
     */
    public void onViewDetachedFromWindow(VH holder) {
    }

    ... ...
}

2.RecyclerView提供了OnChildAttachStateChangeListener接口：

public interface OnChildAttachStateChangeListener {

    /**
     * Called when a view is attached to the RecyclerView.
     *
     * @param view The View which is attached to the RecyclerView
     */
    void onChildViewAttachedToWindow(View view);

    /**
     * Called when a view is detached from RecyclerView.
     *
     * @param view The View which is being detached from the RecyclerView
     */
    void onChildViewDetachedFromWindow(View view);
}

上面的两对接口函数，根据情况选用其一就好了，基本实现逻辑：

1. 设置两个变量，一个用来保存AttachedToWindow被调用时的时间戳，一个用来保存显示的总时长
2. DetachedFromWindow被调用时，计算与AttachedToWindow的时间戳差值，并将AttachedToWindow的时间戳清零，然后总时长加上这个差值
3. AttachedToWindow后，DetachedFromWindow未被调用前，只需获取当前系统时间戳，然后计算与AttachedToWindow的时间戳差值，再加上总时长，就是总时长

Answer 2

可以使用HashMap记录， 在bind时， position 为key， value为一个entity， 含start和end两个成员，设置一个标记， 记录是否已经记录过时间。

Answer 3

第一次显示的时候获取系统时间来作为初始时间，再次显示的时候已当前系统时间减去第一次的时间

Answer 4

尝试使用，这个监听：

ViewTreeObserver.OnGlobalLayoutListener

参考：

• Handle a view visibility change without overriding the view
• view变化监听器ViewTreeObserver介绍
• Viewtreeobserver解析