Expandable WinForms TextBox

Question

I have created a textbox in a Windows Forms application that starts out at a height for entering text in a single line. But I would like the textbox to automatically increase its height if the user enters text that is wrapped within the control.

Currently, for this textbox, I have the properties multiline and wordwrap set to true. I've tried using the TextChanged event to determine when the text has been wrapped but I'm unable to find any property that will help me with this. The Lines property does not provide any help with wrapped text; only for text that the user has hit enter to begin a new line.

How can I get my textbox to expand its height each time the text wraps past the width of the textbox?

Answer 1

If you're willing to use a RichTextBox instead (which, in my experience, is kind of a grumpy control that comes with lots of quirks), you can use the ContentsResized event, which gives you the new required size:

private void HandleContentsResized(object sender, ContentsResizedEvenetArgs e)
{
    int newheight = e.NewRectangle.Height;
}

Answer 2

Unfortunately, I can't provide specifics but you are going to need to probably do a custom implementation.

I'd derive a new text box type -- ExpandableTextBox -- and then you'll need to implement it by hand.

This also seems relevant to what you are looking for: http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/11dfb280-b113-4ddf-ad59-788f78d2995a

Answer 3

Same kind of idea as others have posted, put this in your textChanged event:

Dim s As SizeF = TextRenderer.MeasureText(txt.Text, txt.Font, txt.ClientRectangle.Size, TextFormatFlags.WordBreak)
txt.Height = CInt(s.Height)

You will need some kind of minimum height, and possibly to specify some padding, but this does work.

Answer 4

I'm using the code below with success until about the 10th line, then it gets 1 character off, but this works for me. Don't ask me about the random numbers like - 7 and - 12, they have something to do with padding

    private void txbDescription_TextChanged(object sender, EventArgs e)
    {
        SizeF s = TextRenderer.MeasureText(txbDescription.Text, txbDescription.Font, txbDescription.ClientRectangle.Size, TextFormatFlags.TextBoxControl);

        int lines = (int)Math.Ceiling((decimal)Convert.ToInt32(s.Width - 7) / ((decimal)txbDescription.Width - 12));

        if (lines == 0)
        {
            txbDescription.Height = 20;
        }
        else
        {
            txbDescription.Height = 20 + (lines - 1) * 13;
        }
    }

Answer 5

I just wrote this for a label control for a different project. I got the code off of code project somewhere I think. Changing it to a Textbox should be as simple as changing the base.

public class GrowLabel : Label
{
    private bool _growing;
    //public bool GrowFontSize { get; set; }

    public GrowLabel()
    {
        AutoSize = false;
        //GrowFontSize = false;
    }

    public override sealed bool AutoSize
    {
        get { return base.AutoSize; }
        set { base.AutoSize = value; }
    }

    private void ResizeLabel()
    {
        if (_growing) return;
        try
        {
            _growing = true;

            var sz = new Size(Width, Int32.MaxValue);
            sz = TextRenderer.MeasureText(Text, Font, sz, TextFormatFlags.WordBreak);
            Height = sz.Height;
        }
        finally
        {
            _growing = false;
        }
    }

    protected override void OnTextChanged(EventArgs e)
    {
        base.OnTextChanged(e);
        ResizeLabel();
    }

    protected override void OnFontChanged(EventArgs e)
    {
        base.OnFontChanged(e);
        ResizeLabel();
    }

    protected override void OnSizeChanged(EventArgs e)
    {
        base.OnSizeChanged(e);
        ResizeLabel();
    }
}

Answer 6

AdamSane's post was helpful but the textbox didn't grow. I'd to make some modifications. My mods are below:

class GrowTextBox : TextBox
{
    private double m_growIndex = 0.0;
    private Timer m_timer;

    public GrowTextBox()
    {
        AutoSize = false;
        this.Height = 20;

        // Without the timer, I got a lot of AccessViolationException in the System.Windows.Forms.dll.
        m_timer = new Timer();
        m_timer.Interval = 1;
        m_timer.Enabled = false;
        m_timer.Tick += new EventHandler(m_timer_Tick);

        this.KeyDown += new KeyEventHandler(GrowTextBox_KeyDown);
    }

    void GrowTextBox_KeyDown(object sender, KeyEventArgs e)
    {
        if (e.Modifiers == Keys.Control && e.KeyCode == Keys.A)
        {
            this.SelectAll();
        }
    }

    void m_timer_Tick(object sender, EventArgs e)
    {
        var sz = new Size(Width, Int32.MaxValue);
        sz = TextRenderer.MeasureText(Text, Font, sz, TextFormatFlags.TextBoxControl);

        m_growIndex = (double)(sz.Width / (double)Width);

        if (m_growIndex > 0)
            Multiline = true;
        else
            Multiline = false;

        int tempHeight = (int)(20 * m_growIndex);

        if (tempHeight <= 20)
            Height = 20;
        else
            Height = tempHeight;

        m_timer.Enabled = false;
    }

    public override sealed bool AutoSize
    {
        get { return base.AutoSize; }
        set { base.AutoSize = value; }
    }


    protected override void OnTextChanged(EventArgs e)
    {
        base.OnTextChanged(e);
        m_timer.Enabled = true;
    }

    protected override void OnFontChanged(EventArgs e)
    {
        base.OnFontChanged(e);
        m_timer.Enabled = true;
    }

    protected override void OnSizeChanged(EventArgs e)
    {
        base.OnSizeChanged(e);
        m_timer.Enabled = true;
    }
}