Resizing a WinForms textbox control based on MaxLength

netresizetextboxwinforms

I've got a situation (a key-based search) where I'm going to have multiple inputs of varying, but constrained, length. So I'm building a common control to use for each input, and this control has a TextBox for use when the input type is free-form text. In that case I'd like the length of the TextBox to reflect the constraint placed on the input based on the TextBox's MaxLength property (or at least on a maximum length of some sort).

How can I do this? I realize this is technically impossible with variable width characters, but I'm interested in getting close. The fields vary in maximum length from 3 characters to around 90.

Best Answer

I would try to avoid this dynamic approach.
Do you really think that it adds value for the user? In my opinion it looks strange, when a common control has a different look all the time. Do you think the user can differ between a textbox that allows 32 characters and one that allows 29 characters? How about extrem values? When e.g. only three characters are allowed - or even 1024.
I'd make the TextBox the same length, always - that is better for your control and easier to implement. When the user needs a hint about the max lenght of the text add a label that says "29 characters left" and that updates during the input ...

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An easy to understand and simple solution.

// Save today's date.
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.net – Making a WinForms TextBox behave like your browser’s address bar

First of all, thanks for answers! 9 total answers. Thank you.

Bad news: all of the answers had some quirks or didn't work quite right (or at all). I've added a comment to each of your posts.

Good news: I've found a way to make it work. This solution is pretty straightforward and seems to work in all the scenarios (mousing down, selecting text, tabbing focus, etc.)

bool alreadyFocused;

...

textBox1.GotFocus += textBox1_GotFocus;
textBox1.MouseUp += textBox1_MouseUp;
textBox1.Leave += textBox1_Leave;

...

void textBox1_Leave(object sender, EventArgs e)
{
    alreadyFocused = false;
}


void textBox1_GotFocus(object sender, EventArgs e)
{
    // Select all text only if the mouse isn't down.
    // This makes tabbing to the textbox give focus.
    if (MouseButtons == MouseButtons.None)
    {
        this.textBox1.SelectAll();
        alreadyFocused = true;
    }
}

void textBox1_MouseUp(object sender, MouseEventArgs e)
{
    // Web browsers like Google Chrome select the text on mouse up.
    // They only do it if the textbox isn't already focused,
    // and if the user hasn't selected all text.
    if (!alreadyFocused && this.textBox1.SelectionLength == 0)
    {
        alreadyFocused = true;
        this.textBox1.SelectAll();
    }
}

As far as I can tell, this causes a textbox to behave exactly like a web browser's address bar.

Hopefully this helps the next guy who tries to solve this deceptively simple problem.

Thanks again, guys, for all your answers that helped lead me towards the correct path.

Best Answer

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.net – Making a WinForms TextBox behave like your browser’s address bar

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