如何檢查列表的數量是否增加？

Question

我有這樣的名單：

List<string> x=new List<string> 

所以，現在我想要做的事當計數正在增加。我試過了：

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

但它沒有奏效。那麼，我可以嘗試什麼？

Answer 1

你不能這樣做，就像你想要做的那樣。 if (x.Count++)沒有任何意義 - 您正在嘗試增量計數（它是隻讀的）。

我會從List<T>派生並添加ItemAdded和ItemRemoved事件。

其實，這將重新發明車輪。這樣一個集合已經存在。見ObservableCollection<T>，這引發了一個CollectionChanged事件。 NotifyCollectionChangedEventArgs告訴你什麼改變。

實施例（未測試）：

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