C＃按钮仅在第二次单击时触发

Question

I have done a simple windows form. My button is firing only on the second click. Why is that ?

private void button1_Click(object sender, EventArgs e)
{
    //button1.Enabled = false; will disable the button before the event is fired
    this.button1.Click += new System.EventHandler(this.dosomething);
}

private void dosomething(object sender, System.EventArgs e)
{
    listBox1.Items.Add("Initializing :" + cart + "...");
    this.button1.Click -= new System.EventHandler(this.dosomething);
}

Can some one explain this.

Answer 1

That's exactly what you told it to do.

   this.button1.Click += new System.EventHandler(this.dosomething);

This line adds a handler to the click event, which will run for all future clicks.

Answer 2

As other said you hook up the event only on the first click.

Place this line in the form_load event

this.button1.Click += new System.EventHandler(this.dosomething);

Answer 3

Because you're hooking it up on the first click:

this.button1.Click += new System.EventHandler(this.dosomething);

so it's going to take at least one click to get the dosomething method to fire.

One other problem with this approach is that you could end up hooking this event handler up more than once if an exception is thrown. I know you're removing it in the dosomething event, but it would really be better to just hookup this event in the constructor.

Answer 4

What you are trying to do is to remove the bound event from the button after the button was clicked. You can call the event directly by:

private void button1_Click(object sender, EventArgs e)
{
    dosomething(null, null)
}

Answer 5

If you want button to work only 1 time, you can unsuscribe to click event.

private void button1_Click(object sender, EventArgs e)
{
    DoSomething();
    button1.Click -= button1_Click;
}