c# - Autoscale Font in a TextBox Control so that its as big as possible and still fits in text area bounds

Question

I need a TextBox or some type of Multi-Line Label control which will automatically adjust the font-size to make it as large as possible and yet have the entire message fit inside the bounds of the text area.

I wanted to see if anyone had implemented a user control like this before developing my own.

Example application: have a TextBox which will be half of the area on a windows form. When a message comes in which is will be approximately 100-500 characters it will put all the text in the control and set the font as large as possible. An implementation which uses Mono Supported .NET libraries would be a plus.

If know one has implemented a control already... If someone knows how to test if a given text completely fits inside the text area that would be useful for if I roll my own control.

Edit: I ended up writing an extension to RichTextBox. I will post my code shortly once i've verified that all the kinks are worked out.

Answer 1

I had to solve the same basic problem. The iterative solutions above were very slow. So, I modified it with the following. Same idea. Just uses calculated ratios instead of iterative. Probably, not quite as precise. But, much faster.

For my one-off need, I just threw an event handler on the label holding my text.

    private void PromptLabel_TextChanged(object sender, System.EventArgs e)
    {
        if (PromptLabel.Text.Length == 0)
        {
            return;
        }

        float height = PromptLabel.Height * 0.99f;
        float width = PromptLabel.Width * 0.99f;

        PromptLabel.SuspendLayout();

        Font tryFont = PromptLabel.Font;
        Size tempSize = TextRenderer.MeasureText(PromptLabel.Text, tryFont);

        float heightRatio = height / tempSize.Height;
        float widthRatio = width / tempSize.Width;

        tryFont = new Font(tryFont.FontFamily, tryFont.Size * Math.Min(widthRatio, heightRatio), tryFont.Style);

        PromptLabel.Font = tryFont;
        PromptLabel.ResumeLayout();
    }