winform override onload

// form designer
this.Load += Form1_Load;

// Form1.cs
private void Form1_Load(object sender, EventArgs e)
{
    MessageBox.Show("a");
}

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if override OnLoad abstract method which is defined in Form class, call base.OnLoad(e) is required, otherwise, this.Load event cannot get called.

// form designer
this.Load += Form1_Load;

// Form1.cs
private void Form1_Load(object sender, EventArgs e)
{
    MessageBox.Show("a");
}

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e); // if this is commented, event cannot invoke.
}