Accessing Google Account Id /username via Android
How do you access the user's Google Account Id / username in code? I am building an application that will call a web service to store data and I want to identify the identity of the person submitting the data.
I've ran into the same issue and these two links solved for me:
The first one is this one: How do I retrieve the logged in Google account on android phones?
Which presents the code for retrieving the accounts associated with the phone. Basically you will need something like this:
AccountManager manager = (AccountManager) getSystemService(ACCOUNT_SERVICE);
Account[] list = manager.getAccounts();
And to add the permissions in the AndroidManifest.xml
<uses-permission android:name="android.permission.GET_ACCOUNTS"></uses-permission>
<uses-permission android:name="android.permission.AUTHENTICATE_ACCOUNTS"></uses-permission>
Additionally, if you are using the Emulator the following link will help you to set it up with an account : Android Emulator - Trouble creating user accounts
Basically, it says that you must create an android device based on a API Level and not the SDK Version (like is usually done).
This Method to get Google Username:
 public String getUsername() {
    AccountManager manager = AccountManager.get(this);
    Account[] accounts = manager.getAccountsByType("com.google");
    List<String> possibleEmails = new LinkedList<String>();
    for (Account account : accounts) {
        // TODO: Check possibleEmail against an email regex or treat
        // account.name as an email address only for certain account.type
        // values.
        possibleEmails.add(account.name);
    }
    if (!possibleEmails.isEmpty() && possibleEmails.get(0) != null) {
        String email = possibleEmails.get(0);
        String[] parts = email.split("@");
        if (parts.length > 0 && parts[0] != null)
            return parts[0];
        else
            return null;
    } else
        return null;
}
simple this method call ....
And Get Google User in Gmail id::
 accounts = AccountManager.get(this).getAccounts();
    Log.e("", "Size: " + accounts.length);
    for (Account account : accounts) {
        String possibleEmail = account.name;
        String type = account.type;
        if (type.equals("com.google")) {
            strGmail = possibleEmail;
            Log.e("", "Emails: " + strGmail);
            break;
        }
    }
After add permission in manifest;
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.GET_ACCOUNTS" />
Retrieve profile information for a signed-in user Use the GoogleSignInResult.getSignInAccount method to request profile information for the currently signed in user. You can call the getSignInAccount method after the sign-in intent succeeds.
GoogleSignInResult result = 
Auth.GoogleSignInApi.getSignInResultFromIntent(data);
GoogleSignInAccount acct = result.getSignInAccount();
String personName = acct.getDisplayName();
String personGivenName = acct.getGivenName();
String personFamilyName = acct.getFamilyName();
String personEmail = acct.getEmail();
String personId = acct.getId();
Uri personPhoto = acct.getPhotoUrl();
