error cause: unknown, but Android Studio sometimes has this problem.
1. Sometimes because the software is turned off illegally
2. Sometimes the code from someone else’s computer will not run
. Sometimes a file
is missing. 4. Sometimes it is due to the problem of mobile phone terminal
and so on…
solution:
. Click the toolbar

and

–

Build Clean Project
2. Click the toolbar

and

–

An Rebulid Project
in Build can solve a large part of the problem