Access MainWIndow Control from a class in a separate file

Question

I add a TextBlock to the MainWindow in XAML. And I would need to change the TextBlock Text in a separate class resided in a separate .cs file. I tried the following

Answer 1

You mentioned XAML, so I will assume you are talking about a WPF application. the .xaml and .xaml.cs files go hand in hand. If you need to access anything in that "control" you will need to instantiate it or need its reference in the outside class.

As for the error, you declare the tw1 but it is not instantiated - which is the reason you are getting a Null exception error. Doing tw1 = this is also won't work.