Find and Replace using another form - vb.net

Question

I have my frmMainwhich has RichTextBox1 and I have a button btnfind&Replacewhich whose click event pops out another minute form frmFindandReplace which has two textboxes: TextBoxSearch and TextBoxReplace with two buttons: replaceButton and findButton. I cannot seem to get my code for instances of finding a word in textbox and an instance of replacing it. Here is my code:
Public Class frmFindandReplace
Dim txtClientArea As RichTextBox
Private Sub TextBoxSearch_TextChanged(sender As Object, e As EventArgs) Handles TextBoxSearch.TextChanged
End Sub
Private Sub frmFindandReplace_Load(sender As Object, e As EventArgs) Handles MyBase.Load
End Sub
Private Sub replaceButton_Click(sender As Object, e As EventArgs) Handles replaceButton.Click
End Sub
Protected Friend Sub findButton_Click(sender As Object, e As EventArgs) Handles findButton.Click
Dim a As String
Dim b As String
a = TextBoxSearch.Text
b = InStr(StartPosition, a, txtClientArea)
If b Then txtClientArea.Focus()
txtClientArea.SelectionStart = b - 1
txtClientArea.SelectionLength = Len(a)
txtClientArea.ScrollToCaret()
End Sub
The findButton code doesnot even work. Throws an error!
Error 3: Overload resolution failed because no accessible 'InStr' can be called with these arguments:
'Public Function InStr(Start As Integer, String1 As String, String2 As String, [Compare As Microsoft.VisualBasic.CompareMethod = Microsoft.VisualBasic.CompareMethod.Binary]) As Integer': Value of type 'System.Windows.Forms.TextBox' cannot be converted to 'String'.
'Public Function InStr(String1 As String, String2 As String, [Compare As Microsoft.VisualBasic.CompareMethod = Microsoft.VisualBasic.CompareMethod.Binary]) As Integer': Value of type 'System.Windows.Forms.RichTextBox' cannot be converted to 'Microsoft.VisualBasic.CompareMethod'. C:\Users\Joseph GodwinKE\Documents\Visual Studio 2013\Projects\simpleapp\frmFindandReplace.VB 25 13 Simple app
I know I have not done much but am new and all my efforts of searching a solution over the internet have failed! Thank you I hope someone will help me pls.

Answer 1

A few pointers:
InStr returns an integer.
Check the documentation as it'll show you have the search values the wrong way around.
Turn Option Explicit on to help find your issues.
This should work better.
Private Sub findButton_Click(sender As Object, e As EventArgs) Handles findButton.Click
Dim searchString As String
Dim findPos As Integer
Try
searchString = TextBoxSearch.Text
findPos = InStr(txtClientArea.Text, searchString)
If findPos > 0 Then txtClientArea.Focus()
txtClientArea.SelectionStart = findPos - 1
txtClientArea.SelectionLength = searchString.Length
txtClientArea.ScrollToCaret()
Catch ex As Exception
MessageBox.Show(String.Concat("An error occurred: ", ex.Message))
End Try
End Sub

Answer 2

If you want your code work you need to pass the reference to the RichTextBox present in the first form to the findandReplace form.
Otherwise you will not be able to work with that instance of the RichTextBox.
Usually, this means that when you create and open an instance of the findandReplace form you pass the reference to the RichTextBox to work with in the call to the constructor. Something like this
Dim fReplace As frmFindandReplace = New frmFindandReplace(Me.txtClientArea)
fReplace.Show()
Here the New call reaches the constructor of frmfindandReplace. This call is usually hidden by VB.NET but you could add it writing explicit code for it
Public Class frmFindandReplace
Dim txtClientArea As RichTextBox
Public Sub New (ByVal txt as RichTextBox)
txtClientArea = txt
End Sub
Now the global variable txtClientArea inside the findandReplace class is assigned to the existing reference of the RichTextBox present in the first form and you could happily work with it
Protected Friend Sub findButton_Click(sender As Object, e As EventArgs) Handles findButton.Click
Dim a As String
a = TextBoxSearch.Text
Dim position = txtClientArea.Find(a, 0, RichTextBoxFinds.MatchCase)
.....
End Sub
And please make yourself a favor and start using the more complete methods available from the NET Framework library and stop using the old fashioned VBA methods.
For example the RichTextBox has a method that does exactly what you are trying to do in code. Find, search the content of the textbox and if it founds a match it highlight the text and return the starting position of the text.
There is no replace builtin method but having the position and the length is really simple to implement your own replacing code.

Answer 3

You Have defined b as a string. Change it to an integer. Also Instr doesn't allow you to set a start position, just a string to search and the string to search for and optionally the type of search - Binary or Text.
Finally rather than type If b then, use If b>0 then rather than turning off Option Strict. It's always better to write code with Option Strict on as it makes you write better code and in the long run is easier to chase down errors