If it is a one-page app then as you select EditText in the Designer and generate it as a member of the app, it is initialized spontaneously.
Otherwise, you can create it programmatically as follows:
Private EditText1 as EditText
EditText1.Initialize("ed")
In this case you have to initialize it manually as any other control.
then you can use 'ed' for different edittext methods as ed_TextChanged