android批量删除图片,Android RecyclerView单点、批量数据元素项目item的增加、删除和移动...
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
總結
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