将委托订阅事件分配给列表

Question

这是我的问题：我有一个代表我订阅了另一个 class，没关系。我想要的是每次有东西订阅这个委托时它都会引发一个事件告诉我调用列表已经改变以及 +1 或 -1 是如何...... 我在调用列表中搜索了一个 Onchange 事件，但没有找到任何东西..

表格 1:

namespace EventsOnDelegates
{
public delegate void DEL_delegate1(Double AValue);
public delegate void DEL_delegate2(Boolean AsecondValue);

public partial class Form1 : Form
{
    public DEL_delegate1 SetValueCbk;
    public EventHandler InvocationListChange;
    private Form2 FormwithLabel;
    int invoclength;
    public Form1()
    {
        InitializeComponent();
        FormwithLabel = new Form2(this);
        FormwithLabel.Show();  
        /*the question part*/
        /*I'd like to add an onchange event that tells me if the invocation list has changed and how + or -*/
        InvocationListChange += new EventHandler(SetValueCbk.GetInvocationList(),InvocationListHaschanged);          
    }
    protected virtual void InvocationListHaschanged(object sender, EventArgs e)
    {
    invoclength = SetValueCbk.GetInvocationList().Length;
    label1.Text = Convert.ToString(invoclength);
    }
    private void button1_Click(object sender, EventArgs e)
    {
        Random newRandNum = new Random();
        Double newNumber = newRandNum.NextDouble();
        SetValueCbk(newNumber);
    }
}
}

表格 2:

public partial class Form2 : Form
{
    public Form2(){}
    public Form2(Form1 Form1link)
        :this()
    {
        InitializeComponent();
        Form1link.SetValueCbk  += new DEL_delegate1(this.SetValueCbkFN);
    }
    protected void SetValueCbkFN(Double value)
    {
        label1.Text = Convert.ToString(value);
    }
}

感谢帮助！！

Answer 1

您可以对 event 字段使用 explicit event declaration :

private EventHandler meEvent;

public event EventHandler MeEvent
{
    add { meEvent += value; MeEventInvocationListChanged(); }
    remove { meEvent -= value; MeEventInvocationListChanged(); }
}

编辑： （将其放入您的问题中）

您可以创建 :

而不是您的 InvocationListHasChanged 方法

void InvokationListChanged(int dir)
{
    string msg = dir < 0 ? "Someone unsubscribed from the event" : "Someone subscribed to the event";
    if(InvokeRequired)
    {
        Invoke( new MethodInvoker( () => { label1.Text = msg; });
    }
    else
    {
        label1.Text = msg;
    }
}

然后将public DEL_delegate1 SetValueCbk;更改为：

private DEL_delegate1 m_SetValueCbk;

public event Del_delegate1 SetValueCbk
{
    add { m_SetValueCbk+= value; InvokationListChanged(1); }
    remove { m_SetValueCbk-= value; InvokationListChanged(-1); }
}

现在，只要有其他对象订阅 SetValueCbk，您的 label1.Text 就会更改为 "Someone subscribed to the event"，而每当有对象取消订阅 SetValueCbk，您的 label1.Text 就会更改至 "Someone unsubscribed from the event"

将委托订阅事件分配给列表

assigning delegate subscribe event to a List

c#

events

delegates

onchange