Public Class frmXmlEditor
    Public Property FileName As String

    Private Sub frmXmlEditor_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        If FileName Is Nothing OrElse FileName = String.Empty Then
            MsgBox("Kein Dateiname übergeben!", MsgBoxStyle.Critical, Text)
            Exit Sub
        End If

        If Not IO.File.Exists(FileName) Then
            MsgBox("Datei existiert nicht!", MsgBoxStyle.Critical, Text)
            Exit Sub
        End If

        Try
            Dim oContents = IO.File.ReadAllText(FileName)
            RichEditControl1.Text = oContents
        Catch ex As Exception
            MsgBox($"Fehler beim Laden der Datei: {ex.Message}", MsgBoxStyle.Critical, Text)
        End Try

        RichEditControl1.Document.DefaultCharacterProperties.FontName = "Consolas"
        RichEditControl1.Document.DefaultCharacterProperties.FontSize = 9
    End Sub
End Class