Question

我正在玩事件/代表，我经常遇到以下错误：

发生了'System.Reflection.TargetInvocationException'类型的未处理异常   PresentationFramework.dll

附加信息：调用目标引发了异常。

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，我在其他位置有代码来打开TestWindow对象：

TestWindow testWindow = new TestWindow();

testWindow.TestEvent += this.TestMethod;

和

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

Answer 1

您正在构造函数中调用该事件，这意味着在窗口初始化期间，因此TestEvent在此时为空。为TestEvent添加空检查，并在构造函数以外的某个方法中调用它，检查TestEvent是否分配了订阅者，即它是否为空。

编辑：

以下是一些要演示的代码：

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());
        }

C＃event / delegate TargetInvocationException（WPF）

2 个答案: