为什么RecyclerView.OnScrollListener不是一个接口，但抽象类？ [英] Why RecyclerView.OnScrollListener is not an interface but an abstract class?

问题描述

要实现无尽滚动模式到 RecyclerView 我想创建一个类，像

To implement Endless Scroll pattern in to the RecyclerView I want to create a class like

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

由于 EndlessScrollAdapter 应该负责这两个数据的滚动事件处理，这是实现它的最便捷的方式。

Because EndlessScrollAdapter should be responsible for both of the data and scroll event handling, this is the most convenient way to implement it.

不过，由于 recyclerview-v7-21.0.3 ， OnScrollListener 宣布这样

/**
 * 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){}
}

我不能让 EndlessScrollAdapter 实施 OnScrollListener 。

所以，正如标题所说，有没有什么好的理由 OnScrollListener 是一个类，而不是一个接口？因为我认为它应该是一个接口。

So as the title says, is there any good reason for OnScrollListener to be a class rather than an interface? Because I think it should be an interface.

推荐答案

我有同样的问题，它肯定是设计，因为在这个错误报告回答：

I had the same question, and it's definitely as designed, as answered in this bug report:

<一个href="https://$c$c.google.com/p/android/issues/detail?id=79283">https://$c$c.google.com/p/android/issues/detail?id=79283

抽象类允许的框架，以增加新的方法不会破坏现有实现。

Abstract classes allow frameworks to add new methods without breaking existing implementations.

也介绍了它可以在这里找到的差异：

Also the diff that introduced it can be found here:

<一个href="https://android.googlesource.com/platform/frameworks/support/+/cef7b49%5E!/">https://android.googlesource.com/platform/frameworks/support/+/cef7b49%5E!/

这个变化增加了RecyclerView作为第一个参数滚动相关的回调。

This change adds RecyclerView as a first parameter to the scroll related callbacks.

这也fxies一个在那里滚动回调是被称为瓦特/预期滚动的bug   量，而不是真正的滚动量。

It also fxies a bug where scroll callback was being called w/ the intended scroll amount instead of the real scroll amount.

我也改变了它是一个抽象类，而不是一个接口，使未来   更改更加容易。

I also changed it to be an abstract class instead of an interface to make future changes easier.

不知道我同意了变化，个人，但亚去。

Not sure I agree with the change, personally, but there ya go.

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