为什么我的"事件"总是为空？

Question

我正在尝试连接一个新事件,但出于某种原因,"Changed"总是评估为null

    public class MyTreeViewItem : INotifyPropertyChanged

{
        private MyTreeViewItem _parent;

        public MyTreeViewItem(MyTreeViewItem parent)
        {
            _parent = parent;
        }

        private bool _checked;
        public bool Checked
        {
            get
            {
                return _checked;
            }
            set
            {
                if (value != _checked)
                {
                    _checked = value;
                    OnChanged("test");
                    OnPropertyChanged("Checked");
                }
            }
        }

        public event EventHandler Changed;

        public ObservableCollection<MyTreeViewItem> Children { get; set; }

    // Invoke the Changed event; called whenever list changes
    protected virtual void OnChanged(string test)
    {
        if (Changed != null)
            Changed(this, null);
    }

订阅代码(PropertyChanged Works,Changed没有)

_playgroupTree = new MyTreeViewItem(null);
AddChildNodes(4, ref _playgroupTree);
_playgroupTree.Changed += new EventHandler(_playgroupTree_Changed);
_playgroupTree.PropertyChanged += new PropertyChangedEventHandler(_playgroupTree_PropertyChanged);

真的很奇怪,因为我也在实现INotifyPropertyChanged(它的工作原理),这段代码几乎完全一样(我尝试使用相同的deligate类型,但它仍然不起作用.

我一直在使用这个网站作为参考 http://msdn.microsoft.com/en-us/library/aa645739%28VS.71%29.aspx

Answer 1

好吧,你没有显示任何订阅该事件的代码.你在哪里有这样的代码:

YourClass yc = new YourClass();
yc.Changed += SomeHandler;

？如果您可以生成一个简短但完整的程序来演示问题,那么诊断起来会容易得多.