Calling Control_MouseDown

[Digitborn]

Hello,


How to call the code below:

            
private void Control_MouseDown(System.Object sender,
                System.Windows.Forms.MouseEventArgs e)
            {
                Control control = (Control)sender;
                if (control.Capture)
                {
                    TextBox1.Text = control.Name + " has captured the mouse";
                }
            }

from a Button1 Click event:

            private void Button1_Click(object sender, EventArgs e)
            {
                //this code doesn't work - returns invalid arguments
               Control_MouseDown(sender, control)
            }

[demausdauth]

You need to match the signature. The MouseDown event requires that 2 things are passed to it:

1) An object (This is generally the control that raised the event)
2) An object of System.Windows.Forms.MouseEventArgs

So you could do this...

Control_MouseDown(sender, new System.Windows.Forms.MouseEventArgs(System.Windows.Forms.MouseButtons.Left, 0,1,1,0));

It is hard to figure out what to give you for an answer as it isn't easy to understand what you are attempting.

[Digitborn]

Thanks I get the point and do what I need

[jmcilhinney]

The simple fact is that you shouldn't be calling that event handler directly.

private void Control_MouseDown(Object sender, MouseEventArgs e)
{
    Control control = (Control) sender;
 
    this.IdentifyMouseCapture(control);
}
 
private void Button1_Click(object sender, EventArgs e)
{
    Control control = (Control)sender;
 
    this.IdentifyMouseCapture(control);
}
 
private void IdentifyMouseCapture(Control ctl)
{
    if (ctl.Capture)
    {
        textBox1.Text = ctl.Name + " has captured the mouse";
    }
}

[Digitborn]

Hi,

Can you give me more info why shouldn't be calling event handler directly? I believe you, but i just want to understand it.
For me at this stage seems more complicated to call one more procedure - IdentifyMouseCapture.

[jmcilhinney]

An event handler is a method so you certainly can call it directly if you want to. The thing is, by creating "fake" arguments for an event handler you can get into the situation where you're not dealing with the data you think you are. This is one of those situations where if you just make a rule not to call event handlers directly then you can never get it wrong. It's very simple to structure your code not to have to call an event handler so you may as well do so.

[Digitborn]

1. When I call an event handler I thought I can call arguments, like any other procedure. I didn't know these arguments are a kind of "fake" arguments. I still didn't learn the conception around arguments in event handlers, that's why in my first post I asked such a beginner question.

2. Do you know some proper articles/sample code around that topic? Especially about calling directly and not calling directly pros+/cons-?

[cdaq]

The "fake" parameter you are passing is the MouseEventArgs object that you are creating.

You will run into this situation pretty frequently. The pattern that works in most cases is to factor out the common code into it's own function and then call the re-factored function as needed (just as jmcilhinney suggested) instead of the event handler.

[jmcilhinney]

The arguments received by an event handler are created by the object that raised the event. If there's no event and you created the arguments yourself then they are obviously fake, becaue they don't represent a real event.

You don't need a tutorial for this because it's pretty simple: event handlers are supposed to handle events. If there's no event there should be no event handler. You can call one directly because it's still a method. Doing so saves you having to write a separate method but, as one of our main aims when writing code is clarity, we shouldn't create a less clear, possibly problematic situation to save a few keystrokes.