Line height RichTextBox

[i00]

I was wondering how I would go about getting the height of a line in a RichTextBox from a character index.
When I say line I don't mean split by line breaks but lines as they are displayed on the screen (with word breaks).
I need it to take into consideration the actual height that is taken up by that line ... which won't necessarily be the height of the font as there may be a larger font on that line later that makes the line larger.

How can I go about this?

On a side note I have always thought that the implementation of the RichTextBox was a little dodgy... so i preferably don't want a dodgy way to do this.

Thanks in advance,
Kris

[jmcilhinney]

I'm not aware of anything built into the RichTextBox control to do that. All I can think of is checking all the Fonts used on the line containing that character and taking the largest one.

[Joacim Andersson]

The event ContentsResized is raised when the text of a RichTextBox is, well resized. So if you could copy the line with all the formatting you might be able to put it inside another (hidden or in memory) RichTextBox and use this event to get the new rectangele size.

Private Sub HiddenRTB_ContentsResized(sender As Object, e As ContentsResizedEventArgs)
  _lineHeight = e.NewRectangle.Height
End Sub

I know, it's a bit of a hack but it might work for you.

[Inferrd]

Not tested, but:

Get your known character's position in the RTB (.GetPositionFromCharIndex method)
Get the line number that your character is on (.GetLineFromCharIndex method)
Add 1 to give the next line
Get the character index of the first character on that next line(.GetFirstCharIndexFromLine method)
Get the position of that character within the RTB (.GetPositionFromCharIndex method)

Subtracting the Y coordinates of the two position values should give the line height



To get the height of the last line, I think you'll need to ensure the text always ends with a hard line break. Might be a problem.

[Inferrd]

For example, if you have a RichTextBox named RTB that contains rich text, add the following MouseUp event handler, and select a character on a line:

Private Sub RTB_MouseUp(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles RTB.MouseUp
    RTB.Refresh()

    Dim thisCharIndex As Integer = RTB.GetCharIndexFromPosition(e.Location)

    Dim lineHeight As Integer

    Dim thisCharPos As Point
    Dim thisCharLine As Integer
    Dim nextCharLine As Integer
    Dim nextCharIndex As Integer
    Dim nextCharPos As Point


    thisCharPos = RTB.GetPositionFromCharIndex(thisCharIndex)
    thisCharLine = RTB.GetLineFromCharIndex(thisCharIndex)
    nextCharLine = thisCharLine + 1
    nextCharIndex = RTB.GetFirstCharIndexFromLine(nextCharLine)
    nextCharPos = RTB.GetPositionFromCharIndex(nextCharIndex)

    lineHeight = nextCharPos.Y - thisCharPos.Y


    Using g As Graphics = RTB.CreateGraphics
        Dim rect As New Rectangle(0, thisCharPos.Y, RTB.Width, lineHeight)
        g.DrawRectangle(Pens.Black, rect)
    End Using

End Sub

It's bad code, only meant as a demonstration of the methods used.