How is Form1_Load() invoked by the Load event in Windows Forms?

Question

I'm a rookie in Windows Forms Applications. I have created a Form without any controls added. The following code is generated by the VS compiler

private void InitializeComponent()
{
    this.SuspendLayout();
    // 
    // Form1
    // 
    this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
    this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
    this.ClientSize = new System.Drawing.Size(328, 301);
    this.Name = "Form1";
    this.Text = "Form1";
    this.Load += new System.EventHandler(this.Form1_Load);
    this.ResumeLayout(false);
}

I have found that Load is an event and the Form1 class has Form1_Load() function with arguments. But I couldn't find how that function is invoked by the Load event. How does this call occur?

Answer 1

An event has a certain signature, and the event handler must match this signature.

The default EventHandler delegate has a signature of object sender, EventArgs e, so the event handler method must have this exact same signature:

private void Form1_Load(object sender, EventArgs e)

If it wouldn't, but for example simply be a parameterless method:

private void Form1_Load()

Then this code wouldn't compile:

this.Load += new System.EventHandler(this.Form1_Load);

No overload for 'Form1_Load' matches delegate 'System.EventHandler'

As for who is raising this event and how the arguments are assigned, that's the WinForms engine doing that for you.