How to Adjust Font Size for the Text Fields in PDF Forms

Environment

Product Version	Product	Author
2023.1.314	RadPdfViewer for WinForms	Desislava Yordanova

Description

When a very long text is entered in a text field of a PDF form, the font size remains unchanged and the text is scrolled in the following way:

Default Font Size

Abode offers in the PDF forms text auto-sizing/shrinking functionality so the text can fit in the available box and it is fully visible. This article demonstrates a sample approach how to simulate a similar behavior:

Auto Font Size

Solution

It is possible to change the font size dynamically for the activated editor. For this purpose, it is necessary to measure the text and determine the correct size.

        private void RadPdfViewer1_MouseUp(object sender, MouseEventArgs e)
        {
            foreach (RadFixedPageElement visualPage in this.radPdfViewer1.PdfViewerElement.ViewElement.Children)
            {
                foreach (RadElement editorElement in visualPage.Children)
                {
                    RadTextBoxControlElement tb = editorElement as RadTextBoxControlElement;
                    if (tb != null)
                    {
                        font = tb.Font;
                        tb.TextChanged -= tb_TextChanged;
                        tb.TextChanged += tb_TextChanged;
                    }
                }
            }
        }

        Font font;
        float width;
        float initialFontSize = -1;
        private void tb_TextChanged(object sender, System.EventArgs e)
        {
            RadTextBoxControlElement tb = sender as RadTextBoxControlElement;
            string textToMeasure = tb.Text;
            float fontSize = tb.Font.Size;
            if (initialFontSize == -1)
                initialFontSize = tb.Font.Size;
            SizeF measured = TextRenderer.MeasureText(textToMeasure, font);
            width = tb.Size.Width;

            if (measured.Width > width)
            {
                do
                {
                    fontSize = Math.Max(0, fontSize - 1);
                    font = new Font(tb.Font.FontFamily, fontSize, FontStyle.Regular);
                    measured = TextRenderer.MeasureText(textToMeasure, font);
                }
                while (!(measured.Width < width));
            }
            else
                do
                {
                    fontSize = Math.Min(fontSize + 1, initialFontSize);
                    font = new Font(tb.Font.FontFamily, fontSize, FontStyle.Regular);
                    measured = TextRenderer.MeasureText(textToMeasure, font);
                }
                while ((measured.Width < width) && fontSize < initialFontSize);
            tb.Font = font;
        }         

    Private Sub RadPdfViewer1_MouseUp(sender As Object, e As MouseEventArgs)
        For Each visualPage As RadFixedPageElement In Me.RadPdfViewer1.PdfViewerElement.ViewElement.Children
            For Each editorElement As RadElement In visualPage.Children
                Dim tb As RadTextBoxControlElement = TryCast(editorElement, RadTextBoxControlElement)
                If tb IsNot Nothing Then
                    font = tb.Font
                    RemoveHandler tb.TextChanged, AddressOf tb_TextChanged
                    AddHandler tb.TextChanged, AddressOf tb_TextChanged
                End If
            Next
        Next
    End Sub

    Dim font As Font
    Dim width As Double
    Dim initialFontSize As Integer = -1
    Private Sub tb_TextChanged(sender As Object, e As System.EventArgs)
        Dim tb As RadTextBoxControlElement = TryCast(sender, RadTextBoxControlElement)
        Dim textToMeasure As String = tb.Text
        Dim fontSize As Single = tb.Font.Size
        If initialFontSize = -1 Then
            initialFontSize = tb.Font.Size
        End If 
        Dim measured As SizeF = TextRenderer.MeasureText(textToMeasure, font)
        width = tb.Size.Width 

        If measured.Width > width Then

            Do
                fontSize = Math.Max(0, fontSize - 1)
                font = New Font(tb.Font.FontFamily, fontSize, FontStyle.Regular)
                measured = TextRenderer.MeasureText(textToMeasure, font) 
            Loop Until measured.Width < width

        Else

            Do
                fontSize = Math.Min(fontSize + 1, initialFontSize)
                font = New Font(tb.Font.FontFamily, fontSize, FontStyle.Regular)
                measured = TextRenderer.MeasureText(textToMeasure, font)

            Loop Until measured.Width > width Or fontSize <= initialFontSize

        End If
        tb.Font = font 
    End Sub