Flutter example with async events

I learn Flutter and I am lost with quite a simple example: 1. We have a window with an input field, a button("Ok") and a status Text(). 2. When nothing is in the input field, the button cannot be pressed (looks like disabled), otherwise the button is enabled. 3. When the button is pressed, data from the input field is written to a file, with async calls. 4. The Future of async calls are displayed in the Text with the status "Saving..." / "Saved." / "Failed". 5. While the Future is awaiting during "Saving..", the button is also disabled. I need loose coupling between the objects, so the logic between the Button and the Text shall happen via callbacks in the Screen widget (file) and the Button and Text shall be decoupled from themselves.