I bought it because I could study exactly what I wanted at a low price. However, since it was a lecture from two years ago, there were many codes that could not be applied, so I had a hard time. I had problems from the first DSL. There were parts that caused errors even when I changed the code posted in the notice. Fortunately, I had also taken other Hilt lectures, so I was able to write it so that it would run by comparing it with the code I used then. However, I couldn't finish the app because the API used in the lecture was deprecated. If you want to check the example codes for using the MVVM pattern, Hilt, and Firebase, you can buy it, but I don't recommend it to those who want to know in detail why they should be used and how the code works.