Delay using more than one subroutine

[maccarone]

Hi,
I'm using WPF with vb.net for first time, after having used always windows form till now.
I have strange delay in textbox append text functionality.
I'm try to summarize the issue.
I'have the MainWondow xaml where i call other windows like this:

Private Sub Data_Extraction_click()

Dim Data_Extraction_Instance as new Data_extraction​

Data_Extracion_Instance.ShowDialog()​

End Sub

In the Data_Extraction.vb file I have:

Public Class Estrazione_dati

Private Execute_Extraction ()​

'In the xaml file there is an action linked to a button in a click event for this sub
End Sub

Private Execute Extraction ()

Texbox.AppendText(Environment.NewLine & "Start Sub 1 ")​

Call Sub1()​

Texbox.AppendText(Environment.NewLine & "End Sub 1 ")​

Texbox.AppendText(Environment.NewLine & "Start Sub 2 ")​

Call Sub2()​

Texbox.AppendText(Environment.NewLine & "End Sub 1 ")​

End Sub
End Class

The problem is that the text in the textbox is not showed step by step but all the sentences are showed at the end of the last sub (that is the 8, in the example I've written 2 sun just as example).
When I used the same approach in Windows Form I was able to see the text in the textbox as soon as the text was appended by code.
I don't understand why in WPF the behaviour is different.

Tanks Massimo