How to create data bound textbox in edit-dialog


I want to create a databound textBox that displays a itemnumber in a edit-page when the edit-page is opend.

I have tried to follow this article:

I have converted the edit-page to a template
I have add a textbox
In the page load event of the edit-page I have add this:

Type: Set property
Name: data
Value: {itemnumber: 'item number'}

"itemnumber" is a column of the table that is related to the edit-page.

In the TextBox I have set the Value property to ${data.itemnumber}

But when I start the app and open the edit-dialog then the textBox is empty

Can you paste here the JSON contents of that page? It is in the meta\page-name.json file.