[Motaz Alnuweiri]

تفضل أخي

كود :

'كود جلب أسماء كل الطابعات المثبتة على الجهاز
Public Sub LoadAllPrinters()
    For Each Name As String In Printing.PrinterSettings.InstalledPrinters
        ComboBox1.Items.Add(Name)
    Next

    Dim PrintDoc As New Printing.PrintDocument()
    ComboBox1.Text = PrintDoc.PrinterSettings.PrinterName
End Sub

'كود تعيين الطابعة الافتراضية
Public Function SetDefaultPrinter(ByVal Name As String) As Boolean
    Dim PrintDoc As New Printing.PrintDocument()
    Dim WshNetwork As Object = Nothing
    Dim OldPrinterName As String = String.Empty

    Try
        OldPrinterName = PrintDoc.PrinterSettings.PrinterName
        WshNetwork = Microsoft.VisualBasic.CreateObject("WScript.Network")
        WshNetwork.SetDefaultPrinter(Name)
        PrintDoc.PrinterSettings.PrinterName = Name

        If PrintDoc.PrinterSettings.IsValid Then
            Return True
        Else
            WshNetwork.SetDefaultPrinter(OldPrinterName)
            Return False
        End If

    Catch ex As Exception
        If WshNetwork IsNot Nothing Then
            WshNetwork.SetDefaultPrinter(OldPrinterName)
        End If

    Finally
        PrintDoc = Nothing
        WshNetwork = Nothing
    End Try

    Return False
End Function

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    LoadAllPrinters()
End Sub

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    If SetDefaultPrinter(ComboBox1.Text) Then
        MessageBox.Show(String.Format("الطابعة ""{0}"" أصبحت هي الطابعة الافتراضية", ComboBox1.Text),
                        "الطابعة", MessageBoxButtons.OK, MessageBoxIcon.Information,
                        MessageBoxDefaultButton.Button1, MessageBoxOptions.RtlReading)
    End If
End Sub

المرجع: Setting Windows default printer