如何檢查列表數量是否在增加？

Question

我有這個清單：

List<string> x=new List<string>

所以，現在我想在增加計數時做點什么。 我試過了：

if(x.Count++){
  //do stuff
}

但這沒有用。 那我該怎么辦？

Answer 1

您無法像嘗試那樣去做。 if (x.Count++)沒有意義-您正在嘗試增加計數（只讀）。

我將從List<T>派生並添加ItemAdded和ItemRemoved事件。

實際上，那將是在重新發明輪子。 這樣的集合已經存在。 請參見ObservableCollection<T> ，它引發一個CollectionChanged事件。 NotifyCollectionChangedEventArgs告訴您更改了什么。

示例（未經測試）：

void ChangeHandler(object sender, NotifyCollectionChangedEventArgs e ) {
    switch (e.Action) {
        case NotifyCollectionChangedAction.Add:
            // One or more items were added to the collection.
            break;
        case NotifyCollectionChangedAction.Move:
            // One or more items were moved within the collection.
            break;
        case NotifyCollectionChangedAction.Remove:
            // One or more items were removed from the collection.
            break;
        case NotifyCollectionChangedAction.Replace:
            // One or more items were replaced in the collection.
            break;
        case NotifyCollectionChangedAction.Reset:
            // The content of the collection changed dramatically.
            break;
    }

    // The other properties of e tell you where in the list
    // the change took place, and what was affected.
}

void test() {
    var myList = ObservableCollection<int>();
    myList.CollectionChanged += ChangeHandler;

    myList.Add(4);
}

參考文獻：

• NotifyCollectionChangedAction