Question

HI,
I am developing an editor using RichTextBox in WPF, i have to implement feature that user can set font of selected Text if some text is selected, if nothing is selected then font should be set for new text.
If i set the font properties(like FontStyle,FontSize) of RTB in later case it will set the properties for whole text, How can i set font properties for new text(i.e if user enter the text it will come with new font setting).

Answer 1

I’ve implemented a toolbar that can change the font size, family, color, etc. What i found is the details can be tricky with the wpf richtextbox. Setting the selection font makes some sense, but, there are also the default font properties of the text box, and the current caret properties to contend with. Here is what i’ve written to get it to work for most cases with the font size. The process should be the same for fontfamily and fontcolor. Hope it helps.

    public static void SetFontSize(RichTextBox target, double value)
    {
        // Make sure we have a richtextbox.
        if (target == null)
            return;

        // Make sure we have a selection. Should have one even if there is no text selected.
        if (target.Selection != null)
        {
            // Check whether there is text selected or just sitting at cursor
            if (target.Selection.IsEmpty)
            {
                // Check to see if we are at the start of the textbox and nothing has been added yet
                if (target.Selection.Start.Paragraph == null)
                {
                    // Add a new paragraph object to the richtextbox with the fontsize
                    Paragraph p = new Paragraph();
                    p.FontSize = value;
                    target.Document.Blocks.Add(p);
                }
                else
                {
                    // Get current position of cursor
                    TextPointer curCaret = target.CaretPosition;
                    // Get the current block object that the cursor is in
                    Block curBlock = target.Document.Blocks.Where
                        (x => x.ContentStart.CompareTo(curCaret) == -1 && x.ContentEnd.CompareTo(curCaret) == 1).FirstOrDefault();
                    if (curBlock != null)
                    {
                        Paragraph curParagraph = curBlock as Paragraph;
                        // Create a new run object with the fontsize, and add it to the current block
                        Run newRun = new Run();
                        newRun.FontSize = value;
                        curParagraph.Inlines.Add(newRun);
                        // Reset the cursor into the new block. 
                        // If we don't do this, the font size will default again when you start typing.
                        target.CaretPosition = newRun.ElementStart;
                    }
                }
            }
            else // There is selected text, so change the fontsize of the selection
            {
                TextRange selectionTextRange = new TextRange(target.Selection.Start, target.Selection.End);
                selectionTextRange.ApplyPropertyValue(TextElement.FontSizeProperty, value);
            }
        }
        // Reset the focus onto the richtextbox after selecting the font in a toolbar etc
        target.Focus();
    }