c# - C# 事件/委托 TargetInvocationException (WPF)

Question

我正在玩活动/代表，我经常收到以下错误：

PresentationFramework.dll 中出现“System.Reflection.TargetInvocationException”类型的未处理异常

附加信息：调用的目标已引发异常。

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

您在构造函数中调用事件，这意味着在窗口初始化期间，因此当时TestEvent为 null。为 the 添加一个空检查TestEvent并在构造函数之外的某个方法中调用它，检查是否TestEvent有一个订阅者分配给，即它不为空。

编辑：

下面是一段代码来演示：

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

您在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());
        }