Why MainActivity.java showing error?

[Nora Morris]

I've designed the front-end and opened the MainActivity.java.
When I hover my mouse over the error, It says "cannot resolve symbol R"

Please help me to rectify this issue!

[Norm Radder]

"cannot resolve symbol R"  

The R class is generated by the IDE after all the bits and pieces of the project have been checked.  Most often there is an error in an xml file that is sort of hidden and requires you to look in all the folders with xml files (eg res) to see if any of them are flagged as having errors.

[Nora Morris]

Guys, I solved the issue
Go to File -> Invalidate Caches / Restart... -> Invalidate and Restart.
It worked for me!

[John Joe]

Sometimes this happened because of the package name  named wrongly

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.example.seng.myapplication">

 // named wrongly

[Nora Morris]

John Joe wrote:Sometimes this happened because of the package name  named wrongly

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.example.seng.myapplication">

 // named wrongly

Okay I got it! Thanks for helping me