C# – Create empty C# event handlers automatically

\clrcdelegatesevents

It is not possible to fire an event in C# that has no handlers attached to it. So before each call it is necessary to check if the event is null.

if ( MyEvent != null ) {
  MyEvent( param1, param2 );
}

I would like to keep my code as clean as possible and get rid of those null checks. I don't think it will affect performance very much, at least not in my case.

MyEvent( param1, param2 );

Right now I solve this by adding an empty inline handler to each event manually. This is error prone, since I need to remember to do that etc.

void Initialize() {
  MyEvent += new MyEvent( (p1,p2) => { } );
}

Is there a way to generate empty handlers for all events of a given class automatically using reflection and some CLR magic?

Best Answer

I saw this on another post and have shamelessly stolen it and used it in much of my code ever since:

public delegate void MyClickHandler(object sender, string myValue);
public event MyClickHandler Click = delegate {}; // add empty delegate!

//Let you do this:
public void DoSomething() {
    Click(this, "foo");
}

//Instead of this:
public void DoSomething() {
    if (Click != null) // Unnecessary!
        Click(this, "foo");
}

* If anyone knows the origin of this technique, please post it in the comments. I really do believe in the source getting due credit.

(Edit: I got it from this post Hidden Features of C#?)

Related Solutions

C# – Create Generic method constraining T to an Enum

Since Enum Type implements IConvertible interface, a better implementation should be something like this:

public T GetEnumFromString<T>(string value) where T : struct, IConvertible
{
   if (!typeof(T).IsEnum) 
   {
      throw new ArgumentException("T must be an enumerated type");
   }

   //...
}

This will still permit passing of value types implementing IConvertible. The chances are rare though.

C# – How to remove all event handlers from an event

I found a solution on the MSDN forums. The sample code below will remove all Click events from button1.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        button1.Click += button1_Click;
        button1.Click += button1_Click2;
        button2.Click += button2_Click;
    }

    private void button1_Click(object sender, EventArgs e)  => MessageBox.Show("Hello");
    private void button1_Click2(object sender, EventArgs e) => MessageBox.Show("World");
    private void button2_Click(object sender, EventArgs e)  => RemoveClickEvent(button1);

    private void RemoveClickEvent(Button b)
    {
        FieldInfo f1 = typeof(Control).GetField("EventClick", 
            BindingFlags.Static | BindingFlags.NonPublic);

        object obj = f1.GetValue(b);
        PropertyInfo pi = b.GetType().GetProperty("Events",  
            BindingFlags.NonPublic | BindingFlags.Instance);

        EventHandlerList list = (EventHandlerList)pi.GetValue(b, null);
        list.RemoveHandler(obj, list[obj]);
    }
}

Best Answer

Related Solutions

C# – Create Generic method constraining T to an Enum

C# – How to remove all event handlers from an event

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