gistfile1.txt

accountEditText.addTextChangedListener(accountTextWatcher);
...
...
...

private TextWatcher accountTextWatcher = new TextWatcher() {

		@Override
		public void onTextChanged(CharSequence s, int start, int before, int count) {
		}

		@Override
		public void beforeTextChanged(CharSequence s, int start, int count, int after) {
		}

		@Override
		public void afterTextChanged(Editable s) {
			if (s.length() <= 0) {
				button.setEnable(false);
			} else {
				button.setEnable(true);
			}
		}
	};