Android: How to check if users date is valid

Question

I know there are a lot of questions asked that are related to this but they all seems not to solve my problem. I want to check if the date on the user\'s device is correct, star

Answer 1

You must have server's timestamps to determine if the time in device is fake. Npt pool is a free service to help you get true timestamps.
To use, device must ONLINE, you can not check without the Internet.
Copy class SntpClient to your project: https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/net/SntpClient.java

Code:

SntpClient client = new SntpClient();
long now = -1;
if (client.requestTime("pool.ntp.org", TIME_OUT)) {              
      now = client.getNtpTime();
      if (Math.abs(now - System.currentTimeMillis())    >= ONE_DAY){ 
           // the device's time is wrong
           startErrorActivity();
           ...
      } else {
           // the different time lower than 1 day
           startNextActivity();
      }
} else {
      // something wrong, can't get server's time          
}

Don't forget add INTERNET permission to your manifest