Sending Textbox input to a Visual Basic string in ASP.NET

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VBA

web_development

I'm working on an ASP page that will search for a book by title, author, subject, or keywords. I created variables to hold the information, but when I debug the page, I get a NullReferenceException:

Object reference not set to an instance of an object

How do you reference a string to a textbox? What else should I do to my variables? I hopethis revised code helps.

Public Class Search
	Inherits System.Web.UI.Page

	Dim strTitle As String = Me.TB_Title.Text
	Dim strAuthor As String = Me.TB_Author.Text
	Dim strSubject As String = Me.TB_Subject.Text
	Dim strKeywords As String = Me.TB_Keyword.Text

	Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

	End Sub

	Protected Sub BTN_Submit_Click(ByVal sender As Object, ByVal e As EventArgs) Handles BTN_Submit.Click
		If TB_Title.Text = "" And TB_Author.Text = "" And TB_Subject.Text = "" And TB_Keyword.Text = "" Then
			CV_BlankField.Visible = True
		Else
			CV_BlankField.Visible = False
		End If
	End Sub

	Protected Sub BTN_Clear_Click(ByVal sender As Object, ByVal e As EventArgs) Handles BTN_Clear.Click
		strTitle = ""
		strAuthor = ""
		strSubject = ""
		strKeywords = ""
	End Sub
End Class