recycleView局部更新item notifyItemChanged()几个方法区别

一直只知道recycleview局部刷新就想到notifyItemchanged（）方法，里面传入position即可，用起来的时候是方便，但有时候却不能满足现在的需求，于是就百度。

先看几个常用的刷新方法

notifyDataSetChanged()，

notifyItemChanged(int position)

这两个是再不能常见的。

notifyDataSetChanged()

看源码解释：

/**
 * Notify any registered observers that the data set has changed.
 *
 * 
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.
 *
 * 
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.
 *
 * 
RecyclerView 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.
 *
 * 
If you are writing an adapter it will always be more efficient to use the more
 * specific change events if you can. Rely on notifyDataSetChanged()
 * as a last resort.
 *
 * @see #notifyItemChanged(int)
 * @see #notifyItemInserted(int)
 * @see #notifyItemRemoved(int)
 * @see #notifyItemRangeChanged(int, int)
 * @see #notifyItemRangeInserted(int, int)
 * @see #notifyItemRangeRemoved(int, int)
 */

有道翻译

/ * **通知任何已登记的观察员数据集已更改。*有两类不同的数据更改事件，项目更改和结构更改*更改。项更改是指单个项的数据已更新，但没有位置信息*发生了变化。结构更改是指插入、删除或移动项*在数据集中。** 这个事件没有指定数据集发生了什么变化，强制执行*任何观察员假设所有现有项目和结构可能不再有效。* LayoutManagers将被迫完全重新绑定和转发所有可见视图。**  clerview 将尝试综合可见的结构变化事件*对于报告具有{@link #hasStableIds() stable id}的适配器使用这种方法。这对于动画和视觉的目的是有帮助的*对象持久性，但个别项目视图仍然需要反弹** 如果您正在编写适配器，那么使用越多总是越有效*如果可以的话，具体的变更事件。依靠<代码> notifyDataSetChanged() < /代码>作为最后的手段。**

@see # notifyItemChanged (int)*

@see # notifyItemInserted (int)*

@see # notifyItemRemoved (int)*

@参见#notifyItemRangeChanged(int, int)*

@参见# notifyitemrangeinsert (int, int)*

@参见#notifyItemRangeRemoved(int, int)* /

 

这个是里面的一个方法，回遍历集合，每个改变，我的理解就是会把这个集合下的数据都刷新一下包括控件

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();
    }
}

所以对于这个方法就把所以的控件和数据更新

notifyItemChanged(int position)方法

/**
         * Notify any registered observers that the item at position has changed.
         * Equivalent to calling notifyItemChanged(position, null);.
         *
         *

This is an item change event, not a structural change event. It indicates that any
         * reflection of the data at position is out of date and should be updated.
         * The item at position retains the same identity.

         *
         * @param position Position of the item that has changed
         *
         * @see #notifyItemRangeChanged(int, int)
         */

有道：

/ * **通知任何已登记的观察员，在position处的项目已更改。*相当于调用notifyItemChanged(position, null);。*这是一个项目更改事件，而不是一个结构更改事件。它表明*数据在position处的反射已经过期，需要更新。*位于position的项保留相同的标识。** @param位置已更改项的位置**

@参见#notifyItemRangeChanged(int, int)* /

position是个标识，更改已经修改的地方，内部调用notifyItemRangeChanged(int, int)，从命名就可以看到positionStart从这个位置开始，itemCount这里传入的是1，没有看源码不知道里面是什么情况，有点尴尬，

public void notifyItemRangeChanged(int positionStart, int itemCount,
        @Nullable Object payload) {
    // since onItemRangeChanged() 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).onItemRangeChanged(positionStart, itemCount, payload);
    }
}

这里也是循环对象，不过增加了位置从哪里开始。

上面的两个方法粗略地解释了一下，那么说说另一个方法；

notifyItemChanged(int position, @Nullable Object payload)

是不是很陌生，对于我来说是这样的，以前一般都

notifyDataSetChanged()就ok了

还是先看看官方解释：

/**
 * Notify any registered observers that the item at position has changed with
 * an optional payload object.
 *
 * 
This is an item change event, not a structural change event. It indicates that any
 * reflection of the data at position is out of date and should be updated.
 * The item at position retains the same identity.
 * 
 *
 * 

 * Client can optionally pass a payload for partial change. These payloads will be merged
 * and may be passed to adapter's {@link #onBindViewHolder(ViewHolder, int, List)} if the
 * item is already represented by a ViewHolder and it will be rebound to the same
 * ViewHolder. A notifyItemRangeChanged() with null payload will clear all existing
 * payloads on that item and prevent future payload until
 * {@link #onBindViewHolder(ViewHolder, int, List)} is called. Adapter should not assume
 * that the payload will always be passed to onBindViewHolder(), e.g. when the view is not
 * attached, the payload will be simply dropped.
 *
 * @param position Position of the item that has changed
 * @param payload Optional parameter, use null to identify a "full" update
 *
 * @see #notifyItemRangeChanged(int, int)
 */

有道：

/ * **通知任何已登记的观察员，在position处的项目已更改*一个可选的有效负载对象。*这是一个项目更改事件，而不是一个结构更改事件。它表明*数据在position处的反射已经过期，需要更新。*位于position的项目保持相同的标识。* < / p >** < p >*客户端可以选择性地为部分更改传递有效负载。这些有效载荷将被合并和可能被传递到适配器的{@link #onBindViewHolder(ViewHolder, int, List)}*项目已经由ViewHolder表示，它将被反弹到相同的值* ViewHolder。带有null有效负载的notifyItemRangeChanged()将清除所有现有的数据*有效载荷，并防止未来的有效载荷，直到调用* {@link #onBindViewHolder(ViewHolder, int, List)}。适配器不应假定*有效负载将始终传递给onBindViewHolder()，例如当视图不存在时*附加，有效载荷将被简单地丢弃。**

@param位置已更改项的位置*

@param有效负载可选参数，使用null标识“完整”更新**

@参见#notifyItemRangeChanged(int, int)* /

 

如果看解释的话，一般还不能够理解；payload是一个object对象，可以传入任何，当调用这个方法时候，回调onBindViewHolder(ViewHolder, int, List)，上面已经解释了，payload会被添加到集合中，再onBindViewHolder(ViewHolder, int, List)这个方法中体现出来，这时有点奇怪，这个方法一晃眼没觉得什么但是细心会发现和经常写的有点不一样，

onBindViewHolder(holder, position);是不是少了一个参数，没有list

看看

onBindViewHolder(@NonNull VH holder, int position)官方解释

/**
 * Called by RecyclerView to display the data at the specified position. This method should
 * update the contents of the {@link ViewHolder#itemView} to reflect the item at the given
 * position.
 * 

 * Note that unlike {@link android.widget.ListView}, RecyclerView will not call this method
 * again if the position of the item changes in the data set unless the item itself is
 * invalidated or the new position cannot be determined. For this reason, you should only
 * use the position parameter while acquiring the related data item inside
 * this method and should not keep a copy of it. If you need the position of an item later
 * on (e.g. in a click listener), use {@link ViewHolder#getAdapterPosition()} which will
 * have the updated adapter position.
 *
 * Override {@link #onBindViewHolder(ViewHolder, int, List)} instead if Adapter can
 * handle efficient partial bind.
 *
 * @param holder The ViewHolder which should be updated to represent the contents of the
 *        item at the given position in the data set.
 * @param position The position of the item within the adapter's data set.
 */

有道：

/ * ** clerview调用，显示指定位置的数据。这种方法应该*更新{@link ViewHolder#itemView}的内容，以反映给定的项*位置。* < p >*注意不像{@link android.widget。ListView}，将不会调用此方法*同样，如果项目的位置在数据集中发生变化，除非项目本身发生变化*无效或无法确定新职位。出于这个原因，你只应该*在获取内部相关数据项时，使用position参数*此方法不应保留副本。如果您稍后需要项目的位置* on(例如，在单击侦听器中)，使用{@link ViewHolder#getAdapterPosition()}*更新适配器位置。*如果适配器可以，则覆盖{

@link #onBindViewHolder(ViewHolder, int, List)}处理有效的部分绑定。**

@param持有ViewHolder，它应该被更新为表示*项目位于数据集中给定位置。*

@param定位适配器数据集中项的位置。* /

 

onBindViewHolder(@NonNull VH holder, int position,
        @NonNull List