I want to make an app of Lucky Draw of 7 numbers.When you click the "next number" button each time, it generates a random number. When generating the last number, the app will do the sorting except the last number. After generating the last number, click the button will have no response. You need to click "clear" button to restart. And the numbers cannot repeat. I have tries so many times and it still cannot work. Usually, the app is stopped or cannot generate the numbers one by one. Does anyone know how to do it?