通過標記去除帆布子（

Question

）

我有一個橢圓（前導），我想通過標記（「p」）從帆布（canvas1）中刪除。 我想這一點，但它不工作：

var child = (from c in canvas1.Children 
      where "p".Equals(c.Tag) 
      select c).First(); 
canvas1.Children.Remove(child); 

它給了我這個錯誤：

"Could not find an implementation of the query pattern for source type 'System.Windows.Controls.UIElementCollection'. 'Where' not found. Consider explicitly specifying the type of the range variable 'c'."

我怎麼能按標籤刪除canvas孩子？

Answer 1

的UIElementCollection實現普通的舊IEnumerable，因此是不是默認與LINQ兼容。您需要查詢

var child = (from c in canvas1.Children.Cast<FrameworkElement>() 
      where "p".Equals(c.Tag) 
      select c).First(); 
canvas1.Children.Remove(child); 

注意，這個代碼是suspectible運行時錯誤如果在集合（的UIElement另一個派生）在非FrameworkElement之前將它轉換成一個強類型IEnumerable<T>。爲了防止這種情況，你可能最好去OfType方法

var child = (from c in canvas1.Children.OfType<FrameworkElement>() 
      where "p".Equals(c.Tag) 
      select c).First(); 
canvas1.Children.Remove(child); 

Answer 2

var child = (from FrameworkElement c in canvas1.Children 
      where "p".Equals(c.Tag) 
      select c).First(); 
canvas1.Children.Remove(child); 

或

var child = (from c in canvas1.Children.Cast<FrameworkElement>() 
      where "p".Equals(c.Tag) 
      select c).First(); 
canvas1.Children.Remove(child);