Question

I came to the same question again and again. I need to use the user entered values after a button event, or a doubleclick, or anything. when I do it with the designer, it passes automatically the txt control and its value to the whole program, and I can use it anywhere. But programatically I couldn’t solve it.
here’s a little example:

        private void Form1_Load(object sender, EventArgs e)
    {
        string blabla = "anything";

        Button btn = new Button();
        btn.Location = new Point(10, 40);
        btn.Text = "Click me";
        btn.Click += new EventHandler(btn_Click);
        this.Controls.Add(btn);

    }
    void btn_Click(object sender, EventArgs e)
    {
        MessageBox.Show(blabla);
    }

this doesn’t work, so I added a “public” and the script goes:

    public string blabla;
    private void Form1_Load(object sender, EventArgs e)
    {
        blabla = "anything";

        Button btn = new Button();
        btn.Location = new Point(10, 40);
        btn.Text = "Click me";
        btn.Click += new EventHandler(btn_Click);
        this.Controls.Add(btn);

    }
    void btn_Click(object sender, EventArgs e)
    {
        MessageBox.Show(blabla);
    }

And so I can use my variable with the changed values. This goes well with controls too.
This works, but this makes thousands of public variables in a bigger application. How can I increase the readability by losing these publics? Is there a way to use “ref”? I saw it on the automatic “extract method”, I just don’t know, how can I use that with events.

Maybe I am on the wrong track in this, if there is a shortcut or other solution, please help.

Answer 1

The important change between the two snippets wasn’t the fact that you made the variable public – it’s that you changed it from a local variable in the Form1_Load method into an instance variable. It can still be a private instance variable, if you’re handling it in the same class.

However, another alternative is to keep it as a local variable but use an anonymous function to handle the event:

private void Form1_Load(object sender, EventArgs e)
{
    string blabla = "anything";

    Button btn = new Button();
    btn.Location = new Point(10, 40);
    btn.Text = "Click me";
    btn.Click += (sender, args) => {
        MessageBox.Show(blabla);
        // Other code here, but hopefully not too much...
    };
    this.Controls.Add(btn);
}

(As noted, you don’t want to make the anonymous function too big, for the sake of readability – but it can always call another method with all the appropriate state.)

EDIT: As you’re using VS2005, you’re only using C# 2 so you can’t use lambda expressions. You can use anonymous methods though. The code would then be:

private void Form1_Load(object sender, EventArgs e)
{
    string blabla = "anything";

    Button btn = new Button();
    btn.Location = new Point(10, 40);
    btn.Text = "Click me";
    btn.Click += delegate {
        MessageBox.Show(blabla);
        // Other code here, but hopefully not too much...
    };
    this.Controls.Add(btn);
}