Member Avatar for Dzulham

I'm new in Vb.net and try to make a simple program. I need one variable to be used in all subs. How can i do that with this:

RTB As Richtextbox = CType(TabControl1.SelectedTab.Controls.Item(0), Richtextbox)
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  • Latest Post Latest Post by Dzulham

Dani AI

Generated

was on the right track wanting a single RichTextBox reference for use in multiple subs, and 's pointer to search is fine, but the runtime error happens because the control reference is Nothing when the field is initialized. Initializing a form-level variable from another control at declaration time runs before the designer-created controls exist, so attempting to cast a missing object raises the NullReferenceException (see the .NET docs on NullReferenceException).

A reliable pattern is to declare the variable at class scope but assign it after InitializeComponent has run (for example in Form.Load) or to compute the current RichTextBox on demand. Example: declare the field, then find and store the RichTextBox in Load and update it on tab changes.

Private RTB As RichTextBox

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    RTB = Nothing
    If TabControl1.SelectedTab IsNot Nothing Then
        For Each c As Control In TabControl1.SelectedTab.Controls
            If TypeOf c Is RichTextBox Then
                RTB = CType(c, RichTextBox)
                Exit For
            End If
        Next
    End If
End Sub

An alternative that avoids keeping a possibly stale reference is a read-only property that returns the RichTextBox found in the currently selected tab each time it is needed:

Private ReadOnly Property CurrentRTB As RichTextBox
    Get
        If TabControl1.SelectedTab Is Nothing Then Return Nothing
        For Each c As Control In TabControl1.SelectedTab.Controls
            If TypeOf c Is RichTextBox Then Return CType(c, RichTextBox)
        Next
        Return Nothing
    End Get
End Property

Practical tips: use TryCast when appropriate to avoid exceptions, always check for Nothing before using the reference, and refresh the stored reference in the TabControl.SelectedIndexChanged handler if tabs can change. See the Microsoft documentation on NullReferenceException and the TryCast operator for details.

Member Avatar for Histopathlab

Search in google, you will definitly get information.

Member Avatar for Dzulham

Search in google, you will definitly get information.

I use this,

Public RTB As Richtextbox = CType(TabControl1.SelectedTab.Controls.Item(0), Richtextbox)

Private Sub (Blah Blah) Handles Button1.Click
    If FontDialog1.ShowDialog = Windows.Forms.DialogResult.OK Then
        RTB.Font = FontDialog1.Font
    End If
End Sub

And Get error: Object reference not set to an instance of an object.

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