Get Viewable Text From Textbox

Introduction

This article provides code to get only the viewable text from a textbox. This is useful in case we want to display part of the text which is not viewable on other screens using controls like richtextbox or any other text displaying controls.

Background

This code was developed because of a unique requirement while displaying reports in a project. In the reports there was a textarea for Narration having width = 285 and height=250. So when the user was entering a long text, the RDLC textarea used to clip off the textarea after a specific number of characters. The decision was made to display the remaining text on a supplement report. The challenge was to find the exact number of characters displayed on an RDLC textarea.

To overcome this situation I came up with a solution to have a textbox in runtime have all the same dimensions as that of a textarea in an RDLC report, like font, size, and has the following code to serve the purpose.

The below function accepts two parameters:

1. Textbox which you need to get the viewable text from
2. Number of viewable lines

Private Function GetViewableTextFromTextbox(ByVal textbox As _
           TextBox, ByVal textboxLines As Int32) As String

	Dim prevLineNumber As Integer = 1
	Dim currentLineNumber As Integer = 1
	Dim totalLines As Integer = 1

	Dim visibleText As String = String.Empty

	For charIndex = 0 To textbox.Text.Length - 1
	  visibleText = textbox.Text.Substring(0, charIndex)
	  Dim renderedTxtboxPoint As Point
	  renderedTxtboxPoint = textbox.GetPositionFromCharIndex(charIndex)
	  currentLineNumber = renderedTxtboxPoint.Y
	  If prevLineNumber <> currentLineNumber Then
	    prevLineNumber = currentLineNumber
	    totalLines += 1
	   If totalLines > textboxLines Then
	      GetViewableTextFromTextbox = visibleText
	      Exit For
	   End If
	  End If
	Next

	GetViewableTextFromTextbox = visibleText
End Function

To get the viewable text for your textbox, call it as below:

GetVisibleTextFromTextbox(Textbox1, 18)