RecyclerView Adapter中notifyDataSetChanged 的作用

大家好，又见面了，我是你们的朋友全栈君。

一直认为notifyDataSetChanged  是 用来刷新数据的 当数据发生变化的时候调用notifyDataSetChanged 

官方说：通知任何注册的观察者数据发生了改变(Notify any registered observers that the data set has changed) –自己翻译的不保证完全正确。。。。。。

今天有空翻阅下源码

public final void notifyDataSetChanged() {
    mObservable.notifyChanged();
}

在看看 notifyChanged()方法

public void notifyChanged() {
    // since onChanged() is implemented by the app, it could do anything, including
    // removing itself from {@link mObservers} - and that could cause problems if
    // an iterator is used on the ArrayList {@link mObservers}.
    // to avoid such problems, just march thru the list in the reverse order.
    for (int i = mObservers.size() - 1; i >= 0; i--) {
        mObservers.get(i).onChanged();
    }
}

这里的mObservers 是一个list 

protected final ArrayList<T> mObservers = new ArrayList<T>();

这样看来notifyDataSetChanged 是改变list 的元素

在看下源码的注释 

相似的方法

* @see #notifyItemChanged(int)
* @see #notifyItemInserted(int)
* @see #notifyItemRemoved(int)
* @see #notifyItemRangeChanged(int, int)
* @see #notifyItemRangeInserted(int, int)
* @see #notifyItemRangeRemoved(int, int)

/**
 * Notify any registered observers that the data set has changed.
 *
 * <p>There are two different classes of data change events, item changes and structural
 * changes. Item changes are when a single item has its data updated but no positional
 * changes have occurred. Structural changes are when items are inserted, removed or moved
 * within the data set.</p>
 *
 * <p>This event does not specify what about the data set has changed, forcing
 * any observers to assume that all existing items and structure may no longer be valid.
 * LayoutManagers will be forced to fully rebind and relayout all visible views.</p>
 *
 * <p><code>RecyclerView</code> will attempt to synthesize visible structural change events
 * for adapters that report that they have {@link #hasStableIds() stable IDs} when
 * this method is used. This can help for the purposes of animation and visual
 * object persistence but individual item views will still need to be rebound
 * and relaid out.</p>
 *
 * <p>If you are writing an adapter it will always be more efficient to use the more
 * specific change events if you can. Rely on <code>notifyDataSetChanged()</code>
 * as a last resort.</p>

可以看到官方说 notifyDataSetChanged 的作用

Notify any registered observers that the data set has changed. 通知任何注册的观察者数据发生了改变