android - 为什么RecyclerView.OnScrollListener不是接口(interface)而是抽象类？

为了在RecyclerView中实现Endless Scroll模式，我想创建一个类

public class EndlessScrollAdapter<VH extends ViewHolder>
        extends RecyclerView.Adapter<VH> implements RecyclerView.OnScrollListener {
}

因为EndlessScrollAdapter应该同时负责数据和滚动事件的处理，所以这是实现它的最方便的方法。

但是，因为在recyclerview-v7-21.0.3中，OnScrollListener像这样声明

/**
 * An OnScrollListener can be set on a RecyclerView to receive messages
 * when a scrolling event has occurred on that RecyclerView.
 *
 * @see RecyclerView#setOnScrollListener(OnScrollListener)
 */
abstract static public class OnScrollListener {
    /**
     * Callback method to be invoked when RecyclerView's scroll state changes.
     *
     * @param recyclerView The RecyclerView whose scroll state has changed.
     * @param newState     The updated scroll state. One of {@link #SCROLL_STATE_IDLE},
     *                     {@link #SCROLL_STATE_DRAGGING} or {@link #SCROLL_STATE_SETTLING}.
     */
    public void onScrollStateChanged(RecyclerView recyclerView, int newState){}

    /**
     * Callback method to be invoked when the RecyclerView has been scrolled. This will be
     * called after the scroll has completed.
     *
     * @param recyclerView The RecyclerView which scrolled.
     * @param dx The amount of horizontal scroll.
     * @param dy The amount of vertical scroll.
     */
    public void onScrolled(RecyclerView recyclerView, int dx, int dy){}
}

我无法使EndlessScrollAdapter实现OnScrollListener。

因此，正如标题所述，是否有充分的理由使OnScrollListener成为类而不是接口(interface)？因为我认为它应该是一个接口(interface)。

最佳答案

我有相同的问题，而且绝对是设计合理的问题，如此错误报告中所述:

https://code.google.com/p/android/issues/detail?id=79283



也可以在这里找到引入它的差异:

https://android.googlesource.com/platform/frameworks/support/+/cef7b49%5E!/



我不确定我个人同意更改，但是可以。

关于android - 为什么RecyclerView.OnScrollListener不是接口(interface)而是抽象类？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/28636694/