java - Android DataBinding、onItemrangeMoved - 条目 block 何时在列表中移动？

Question

我目前正在使用 Android 数据绑定(bind)库，它是 ObservableList .

但是方法onItemRangeMovedT(sender,int fromPosition, int toPosition, int itemCount)让我很困惑。

假设参数为 sender = A, B, C, D, E, fromPosition = 0, toPosition = 2, itemCount = 2

据我了解，它会告诉我以下内容:

A                   C
B                   D
C   results in =>   A
D                   B
E                   E

但是这是什么时候发生的呢？ ObservableList 内部是否有一个逻辑，它会监视条目的顺序，并在受到 Collection.sort() 或某些复杂的 Collections.rotate(l.sublist(j, k), x) 刺激时自动调用 onItemRangeMoved ，甚至跟踪团体例如。 [ab]cde -> cd[ab]e?

itemCount 参数真的让我很奇怪。

Answer 1

来自documentation :

void onItemRangeMoved (T sender, // The changing list.
            int fromPosition,    // The position from which the items were moved.
            int toPosition,      // The destination position of the items.
            int itemCount)       // The number of items moved.

Called whenever items in the list have been moved.

<小时/>

深入挖掘ObservableArrayList.class，我们会发现一个ListChangeRegistry.class，它扩展了ObservableList.OnListChangedCallback。从 ObservableArrayList.class 中，您可以找到 set() 等方法:

// mListener is an instance of ListChangeRegistry
@Override
public T set(int index, T object) {
    T val = super.set(index, object);
    if (mListeners != null) {
        mListeners.notifyChanged(this, index, 1);
    }
    return val;
}

这是被调用的方法:

/**
 * Notify registered callbacks that some elements have changed.
 *
 * @param list The list that changed.
 * @param start The index of the first changed element.
 * @param count The number of changed elements.
 */
public void notifyChanged(ObservableList list, int start, int count) {
    ListChanges listChanges = acquire(start, 0, count);
    notifyCallbacks(list, CHANGED, listChanges);
}

哪个调用:

 @Override
 public void onNotifyCallback(ObservableList.OnListChangedCallback callback,
            ObservableList sender, int notificationType, ListChanges listChanges) {
        switch (notificationType) {
            case CHANGED:
                callback.onItemRangeChanged(sender, listChanges.start, listChanges.count);
                break;
            //more cases
        }
}

由于更改、移动等需要有时设置元素，我猜每次都会触发onItemRangeChanged - 正如文档所述。