应用程序启动时的“致命异常：主要”

After following a beginners tutorial I ended up combining a bunch of lessons to create a timer app which takes an amount of time and plays media once the time passes. The app worked perfectly...Yesterday. I don't recall changing anything but when I tried to debug today the app would load to my phone, install, and crash. I get a load of error messages which I don't understand:After following a beginners tutorial I ended up