无法将Button作为参数传递

Question

What I'm trying to do here is really simple but it's not working for me. I've looked up many examples of very similar or matching questions on stackoverflow and others and their solutions haven't worked for me.

Basically (in a very simplified form), I have a button with some text in it. I'd like it so when this button is clicked, a message box shows up displaying the text. However, I have 9 of these buttons (think numbers on a calculator), and I'd like to create a single method that handles all of these clicks, and outputs the correct text depending on the button.. which is why I need to pass the button as a parameter.

Here's the code I have for the method that handles it so far:

private void btn_Click(object sender, EventArgs e, Button b)
{
    MessageBox.Show(b.Text);
}

The above small code snippet is the same solution that others have used and had working. However, for me this code doesn't compile and shows an error that says No overload for 'btn_Click' matches delegate 'System.EventHandler' .

When I double click on that error, it takes me to the Designer.cs page for the form, and this is the line of code that has the error:

this.btnN7.Click += new System.EventHandler(this.btnN7_Click);

I have no clue what the overload and delegate parts mean, sorry I'm pretty new to this. I was thinking that maybe overload has to do with constructors but even if that's correct, I'm unsure of what the next step would be.

I have System.Windows.Forms; included properly so the issue shouldn't be that the Button object wasn't recognized.

If you could provide any insight as to what I'm missing or doing wrong, that'd be very sweet! Please let me know if you need any additional information to continue.

And lastly, this is unrelated to my issue but it's a small question that's been irking me ever since I started using VS a week ago: Are the control parameters object sender and EventArgs e that are automatically created for controller events even necessary? Most of the examples I've looked up online omit them. I've just kept them in since they were created by default but I don't really know what kind of function they provide, and I've never had to use those parameters in my methods.

Thanks all! =)

Answer 1

You just need to use sender parameter.You can't subscribe an event handler if the method signature doesn't match with the EventHandler delegate.

private void btn_Click(object sender, EventArgs e)
{
   var currentButton = sender as Button;
   if(currentButton != null) MessageBox.Show(currentButton.Text);
}

sender will be assigned to an object that triggers the event.So for instance when your button2 is clicked, it will be assigned to button2 .Ofcourse you need to attach this event handler to button2 's Click event.I have also used the as operator to ensure that a button is triggered the event.In the future if you call this method manually like btn_Click(this, EventArgs.Empty) then the explicit cast will throw an InvalidCastException .Using as operator is always better to avoid this.If the type of the sender is different than Button then currentButton will be null .

Answer 2

which is why I need to pass the button as a parameter.

You don't really have to create that extra parameter. What you need is already there.

object sender is a source of the event, so just call

var btn = (Button) sender;
MessageBox.Show(btn.Text);

and you should be fine.

Are the control parameters object sender and EventArgs e that are automatically created for controller events even necessary?

So now you have a part of an answer for this question. The second part ( EventArgs ) are needed for passing additional information. Read more about event args on MSDN .

Answer 3

You have two options here:

• If you want to access to the button that fired the event, you can do it trough sender

   private void btn_Click(object sender, EventArgs e) { Button b = (Button)sender; MessageBox.Show(b.Text); } 

• Otherwise, access directly through the button name (in case you know it)