Select Range of Text in WPF RichTextBox (FlowDocument) Programmatically

I have this WPF RichTextBox and I want to programmatically select a given range of letters/words and highlight it. I've tried this, but it doesn't work, probably because I'm not taking into account some hidden FlowDocument tags or similar. For example, I want to select letters 3-8 but 2-6 gets selected):

var start = MyRichTextBox.Document.ContentStart;
var startPos = start.GetPositionAtOffset(3);
var endPos = start.GetPositionAtOffset(8);
var textRange = new TextRange(startPos,endPos);
textRange.ApplyPropertyValue(TextElement.ForegroundProperty,
    new SolidColorBrush(Colors.Blue));
textRange.ApplyPropertyValue(TextElement.FontWeightProperty, 
    FontWeights.Bold);

I've realised RichTextBox handling is a bit trickier than I thought :)

Update: I got a few answers on the MSDN forums: This thread where "dekurver" seid:

The offsets you're specifying are not character offsets but symbol offsets. What you need to do is get a TextPointer that you know is adjacent to text, then you can add character offsets.

And "LesterLobo" said:

you will need to loop through the paragraphs and inlines to find the Next and then their offsets in a loop to apply for all appearances of the specific text. note that when you edit your text would move but your highlight wouldnt move as its associated with the offset not the text. You could however create a custom run and provide a highlight for it...

Would still LOVE to see some sample code for this if someone knows their way around FlowDocuments...

EDIT I got a version of Kratz VB code working, it looks like this:

private static TextPointer GetPoint(TextPointer start, int x)
{
    var ret = start;
    var i = 0;
    while (i < x && ret != null)
    {
        if (ret.GetPointerContext(LogicalDirection.Backward) == 
TextPointerContext.Text ||
            ret.GetPointerContext(LogicalDirection.Backward) == 
TextPointerContext.None)
            i++;
        if (ret.GetPositionAtOffset(1, 
LogicalDirection.Forward) == null)
            return ret;
        ret = ret.GetPositionAtOffset(1, 
LogicalDirection.Forward);
    }
    return ret;
}

And I use it like this:

Colorize(item.Offset, item.Text.Length, Colors.Blue);

private void Colorize(int offset, int length, Color color)
{
    var textRange = MyRichTextBox.Selection;
    var start = MyRichTextBox.Document.ContentStart;
    var startPos = GetPoint(start, offset);
    var endPos = GetPoint(start, offset + length);

    textRange.Select(startPos, endPos);
    textRange.ApplyPropertyValue(TextElement.ForegroundProperty, 
new SolidColorBrush(color));
    textRange.ApplyPropertyValue(TextElement.FontWeightProperty, 
FontWeights.Bold);
}

Kratz

Public Function GoToPoint(ByVal start As TextPointer, ByVal x As Integer) As TextPointer
    Dim out As TextPointer = start
    Dim i As Integer = 0
    Do While i < x
        If out.GetPointerContext(LogicalDirection.Backward) = TextPointerContext.Text Or _
             out.GetPointerContext(LogicalDirection.Backward) = TextPointerContext.None Then
            i += 1
        End If
        If out.GetPositionAtOffset(1, LogicalDirection.Forward) Is Nothing Then
            Return out
        Else
            out = out.GetPositionAtOffset(1, LogicalDirection.Forward)
        End If


    Loop
    Return out
End Function

Try this, this should return a text pointer for the given char offset. (Sorry its in VB, but thats what I am working in...)

Try that :

var textRange = MyRichTextBox.Selection;
var start = MyRichTextBox.Document.ContentStart;
var startPos = start.GetPositionAtOffset(3);
var endPos = start.GetPositionAtOffset(8);
textRange.Select(startPos, endPos);
textRange.ApplyPropertyValue(TextElement.ForegroundProperty, new SolidColorBrush(Colors.Blue));
textRange.ApplyPropertyValue(TextElement.FontWeightProperty, FontWeights.Bold);

I tried using the solution posted by KratzVB but found that it was ignoring newlines. If you want to count \r and \n symbols then this code should work:

private static TextPointer GetPoint(TextPointer start, int x)
{

        var ret = start;
        var i = 0;
        while (ret != null)
        {
            string stringSoFar = new TextRange(ret, ret.GetPositionAtOffset(i, LogicalDirection.Forward)).Text;
            if (stringSoFar.Length == x)
                    break;
            i++;
            if (ret.GetPositionAtOffset(i, LogicalDirection.Forward) == null)
                return ret.GetPositionAtOffset(i-1, LogicalDirection.Forward)

        }
        ret=ret.GetPositionAtOffset(i, LogicalDirection.Forward);
        return ret;
}

My version based on cave_dweller's version

private static TextPointer GetPositionAtCharOffset(TextPointer start, int numbertOfChars)
{
    var offset = start;
    int i = 0;
    string stringSoFar="";
    while (stringSoFar.Length < numbertOfChars)
    {
        i++;
        TextPointer offsetCandidate = start.GetPositionAtOffset(
                i, LogicalDirection.Forward);

        if (offsetCandidate == null)
            return offset; // ups.. we are to far

        offset = offsetCandidate;
        stringSoFar = new TextRange(start, offset).Text;
    }

    return offset;
}

To omit some characters add this code inside loop:

stringSoFar = stringSoFar.Replace("\r\n", "")
                         .Replace(" ", "")

Instead of this (slow):

var startPos = GetPoint(start, offset);
var endPos = GetPoint(start, offset + length);

You should do this (faster)

var startPos = GetPoint(start, offset);
var endPos = GetPoint(startPos, length);

Or create separate method to get TextRange:

private static TextRange GetTextRange(TextPointer start, int startIndex, int length)
{
    var rangeStart = GetPositionAtCharOffset(start, startIndex);
    var rangeEnd = GetPositionAtCharOffset(rangeStart, length);
    return new TextRange(rangeStart, rangeEnd);
}

You can now format text without Select()ing:

var range = GetTextRange(Document.ContentStart, 3, 8);
range.ApplyPropertyValue(
    TextElement.BackgroundProperty, 
    new SolidColorBrush(Colors.Aquamarine));

Could not find a solution with acceptable performance solution to this problem for a long time. Next sample works in my case with the highest performance. Hope it will help somebody as well.

TextPointer startPos = rtb.Document.ContentStart.GetPositionAtOffset(searchWordIndex, LogicalDirection.Forward);
startPos = startPos.CorrectPosition(searchWord, FindDialog.IsCaseSensitive);
if (startPos != null)
{
    TextPointer endPos = startPos.GetPositionAtOffset(textLength, LogicalDirection.Forward);
    if (endPos != null)
    {
         rtb.Selection.Select(startPos, endPos);
    }
}

public static TextPointer CorrectPosition(this TextPointer position, string word, bool caseSensitive)
{
   TextPointer start = null;
   while (position != null)
   {
       if (position.GetPointerContext(LogicalDirection.Forward) == TextPointerContext.Text)
       {
           string textRun = position.GetTextInRun(LogicalDirection.Forward);

           int indexInRun = textRun.IndexOf(word, caseSensitive ? StringComparison.InvariantCulture : StringComparison.InvariantCultureIgnoreCase);
           if (indexInRun >= 0)
           {
               start = position.GetPositionAtOffset(indexInRun);
               break;
           }
       }

       position = position.GetNextContextPosition(LogicalDirection.Forward);
   }

   return start; 
}

Incidentally (and this may be academic to all but myself), if you set FocusManager.IsFocusScope="True" on the container of the RichTextBox, a Grid for example,

<Grid FocusManager.IsFocusScope="True">...</Grid>

then you should be able to use Johan Danforth's Colorize method without the two invocations of ApplyPropertyValue, and the RichTextBox ought to use the default selection Background and Foreground to highlight the selection.

private void Colorize(int offset, int length, Color color)
{
    var textRange = MyRichTextBox.Selection;
    var start = MyRichTextBox.Document.ContentStart;
    var startPos = GetPoint(start, offset);
    var endPos = GetPoint(start, offset + length);

    textRange.Select(startPos, endPos);
}

Have not tried it with the RichTextBox, but it works quite well when templating a find TextBox in a FlowDocumentReader. Just to be sure you might also set

<RichTextBox FocusManager.FocusedElement="{Binding RelativeSource={RelativeSource Self}}">...</RichTextBox>

to ensure the RichTextBox has focus within its focus scope.

The downside of this, of course, is that if the user clicks or performs a selection within the RichTextBox, your selection disappears.

    private TextPointer GetPoint(TextPointer start, int pos)
    {
        var ret = start;
        int i = 0;
        while (i < pos)
        {
            if (ret.GetPointerContext(LogicalDirection.Forward) ==
    TextPointerContext.Text)
                i++;
            if (ret.GetPositionAtOffset(1, LogicalDirection.Forward) == null)
                return ret;
            ret = ret.GetPositionAtOffset(1, LogicalDirection.Forward);
        }
        return ret;
    }

    private void SelectText(int start, int length)
    {
        TextRange textRange = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
        TextPointer pointerStart = textRange.Start.GetPositionAtOffset(start, LogicalDirection.Forward);
        TextPointer pointerEnd = textRange.Start.GetPositionAtOffset(start + length, LogicalDirection.Backward);

        richTextBox.Selection.Select(pointerStart, pointerEnd);
    }

来源：https://stackoverflow.com/questions/1454440/select-range-of-text-in-wpf-richtextbox-flowdocument-programmatically

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wpf

richtextbox