C# 事件/委托 TargetInvocationException (WPF)

Question

我正在玩事件/委托，我经常收到以下错误：

类型为"System.Reflection.TargetInvocationException"的未处理异常发生在演示框架.dll

其他信息：调用目标已引发异常。

我的代码如下：

namespace Test
{
    using System;
    using System.Windows;
    public partial class TestWindow : Window
    {
        public TestWindow()
        {
            this.InitializeComponent();
            this.TestEvent(this, new EventArgs());
        }
        public delegate void TestDelegate(object sender, EventArgs e);
        public event TestDelegate TestEvent;
    }
}

显然，我在另一个位置有代码来打开 TestWindow 对象：

TestWindow testWindow = new TestWindow();
testWindow.TestEvent += this.TestMethod;

和：

private void TestMethod(object sender, EventArgs e)
{
}

Answer 1

你在构造函数中调用事件，这意味着在窗口初始化期间，所以TestEvent在那个时候是空的。为TestEvent添加一个空检查，并在构造函数以外的某种方法中调用它，检查TestEvent是否分配了订阅者，即它不为空。

编辑：

下面是一些代码来演示：

public partial class TestWindow : Window
    {
        public TestWindow()
        {
            this.InitializeComponent();
            //don't publish event in constructor, since the event yet to have any subscriber
            //this.TestEvent(this, new EventArgs());
        }
        public void DoSomething()
        {
            //Do Something Here and notify subscribers that something has been done
            if (TestEvent != null)
            {
                TestEvent(this, new EventArgs());
            }
        }
        public delegate void TestDelegate(object sender, EventArgs e);
        public event TestDelegate TestEvent;
    }
    public class Subscriber
    {
        public Subscriber(TestWindow win)
        {
            win.TestEvent += this.TestMethod;
        }
        private void TestMethod(object sender, EventArgs e)
        {
            //Do something when the event occurs
        }
    }

Answer 2

方法

调用之前缺少以下行

   TestEvent += new TestDelegate(TestMethod);

构造函数中的正确代码是。

 public TestWindow()
        {
            this.InitializeComponent();
            TestEvent += new TestDelegate(TestMethod);
            this.TestEvent(this, new EventArgs());
        }