Android : How to make button enabled depends on edittext in API 7

I need to setEnabled button when edittext is not empty but project is in API 7.. have to do this for low android :-/ I tried this way:

edittxt.setOnFocusChangeListener(new View.OnFocusChangeListener() {
            @Override
            public void onFocusChange(View view, boolean b) {
            if (!b) {
                if (!edittxt.getText().toString().trim().equals("")) {
                  btn1.setEnabled(true);
                }
            }
            }
        });

App does not work. In API 7 setEnabled() method is not available.. Is there any way how to make it? Thx.