Android RecyclerView單點、批量數據元素項目item的增加、刪除和移動

前文附錄1,2介紹了基本的Android RecyclerView單點、批量元素項目的更新。現在給出其他比較重要的Android RecyclerView數據元素項目的刪除和增加，刪除和增加包含兩種，一種是單點，另外一種是批量的元素。

(一)RecyclerView刪除操作。

(a)單點刪除：notifyItemRemoved(int position)

/**

* Notify any registered observers that the item previously located at position

* has been removed from the data set. The items previously located at and after

* position may now be found at oldPosition - 1.

*

*

This is a structural change event. Representations of other existing items in the

* data set are still considered up to date and will not be rebound, though their positions

* may be altered.

*

* @param position Position of the item that has now been removed

*

* @see #notifyItemRangeRemoved(int, int)

*/

public final void notifyItemRemoved(int position) {

mObservable.notifyItemRangeRemoved(position, 1);

}

在給adapter維持的數據隊列刪除一個元素后，調用此方法，該方法刪除指定位置position的元素并更新RecyclerView。

(b)批量刪除：notifyItemRangeRemoved(int positionStart, int itemCount)

public void notifyItemRangeRemoved(int positionStart, int itemCount) {

// since onItemRangeRemoved() 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).onItemRangeRemoved(positionStart, itemCount);

}

}

在給adapter維持的數據元素隊列批量刪除若干元素后，調用該方法，該方法刪除從開始位置positionStart起之后的itemCount個數量的子元素，然后更新RecyclerView。

(二)RecyclerView增加操作。

(a)單點增加：notifyItemInserted(int position)

/**

* Notify any registered observers that the item reflected at position

* has been newly inserted. The item previously at position is now at

* position position + 1.

*

*

This is a structural change event. Representations of other existing items in the

* data set are still considered up to date and will not be rebound, though their

* positions may be altered.

*

* @param position Position of the newly inserted item in the data set

*

* @see #notifyItemRangeInserted(int, int)

*/

public final void notifyItemInserted(int position) {

mObservable.notifyItemRangeInserted(position, 1);

}在給adapter指定位置position增加一個元素后，調用notifyItemInserted方法，更新RecyclerView。

(b)批量增加：notifyItemRangeInserted(int positionStart, int itemCount)

public void notifyItemRangeInserted(int positionStart, int itemCount) {

// since onItemRangeInserted() 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).onItemRangeInserted(positionStart, itemCount);

}

}在給adapter適配器指定位置positionStart增加itemCount個數據元素后，調用此方法，更新RecyclerView。

(三)RecyclerView移動操作。

notifyItemMoved(int fromPosition, int toPosition)

/**

* Notify any registered observers that the item reflected at fromPosition

* has been moved to toPosition.

*

*

This is a structural change event. Representations of other existing items in the

* data set are still considered up to date and will not be rebound, though their

* positions may be altered.

*

* @param fromPosition Previous position of the item.

* @param toPosition New position of the item.

*/

public final void notifyItemMoved(int fromPosition, int toPosition) {

mObservable.notifyItemMoved(fromPosition, toPosition);

}

移動操作的對象位置有兩個，開始對象位置fromPosition和目的地址位置toPosition。設定這兩個位置后，fromPosition元素位置的元素被移動到toPosition。fromPosition和toPosition是元素的集合隊列中的下標。

附錄：

1，《 Android RecyclerView更新子項目notifyItemChanged》鏈接：http://blog.csdn.net/zhangphil/article/details/78565738

2，《Android RecyclerView批量更新notifyItemRangeChanged》鏈接：http://blog.csdn.net/zhangphil/article/details/78579849

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