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 > 1)
            return parts[0];
    }
    return null;
}

这在Android中是相当棘手的事情，我还没有做过。但也许这些链接可以帮助你:

Android Issue 1073:谷歌认证令牌应该可以通过API访问第三方应用程序 android 2.x+中的SDK API AccountManager

有一个Android api，允许用户选择他们的电子邮件地址，而不需要许可。来看看:https://developers.google.com/identity/smartlock-passwords/android/retrieve-hints

HintRequest hintRequest = new HintRequest.Builder()
        .setHintPickerConfig(new CredentialPickerConfig.Builder()
                .setShowCancelButton(true)
                .build())
        .setEmailAddressIdentifierSupported(true)
        .setAccountTypes(IdentityProviders.GOOGLE)
        .build();

PendingIntent intent = mCredentialsClient.getHintPickerIntent(hintRequest);
try {
    startIntentSenderForResult(intent.getIntentSender(), RC_HINT, null, 0, 0, 0);
} catch (IntentSender.SendIntentException e) {
    Log.e(TAG, "Could not start hint picker Intent", e);
}

这将显示一个选择器，用户可以在其中选择电子邮件地址。结果将在onActivityResult()中传递

有几种方法可以做到这一点，如下所示。

作为一个友好的警告，在处理帐户、个人资料和联系人数据时，要谨慎和坦率地对待用户。如果你误用了用户的电子邮件地址或其他个人信息，就会发生不好的事情。

方法A:使用AccountManager (API级别5+)

您可以使用AccountManager。getAccounts或AccountManager。getAccountsByType获取设备上所有帐户名的列表。幸运的是，对于某些帐户类型(包括com.google)，帐户名称是电子邮件地址。下面是示例片段。

Pattern emailPattern = Patterns.EMAIL_ADDRESS; // API level 8+
Account[] accounts = AccountManager.get(context).getAccounts();
for (Account account : accounts) {
    if (emailPattern.matcher(account.name).matches()) {
        String possibleEmail = account.name;
        ...
    }
}

注意，这需要GET_ACCOUNTS权限:

<uses-permission android:name="android.permission.GET_ACCOUNTS" />

关于使用AccountManager的更多信息可以在SDK中的Contact Manager示例代码中找到。

方法二:使用ContactsContract。简介(API等级14+)

从Android 4.0 (Ice Cream Sandwich)开始，你可以通过访问用户的个人资料来获取用户的电子邮件地址。访问用户配置文件有点重量级，因为它需要两个权限(下文将详细介绍)，但电子邮件地址是相当敏感的数据，因此这是入场费。

下面是一个使用CursorLoader检索包含电子邮件地址的配置文件数据行的完整示例。

public class ExampleActivity extends Activity implements LoaderManager.LoaderCallbacks<Cursor> {
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getLoaderManager().initLoader(0, null, this);
    }

    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle arguments) {
        return new CursorLoader(this,
                // Retrieve data rows for the device user's 'profile' contact.
                Uri.withAppendedPath(
                        ContactsContract.Profile.CONTENT_URI,
                        ContactsContract.Contacts.Data.CONTENT_DIRECTORY),
                ProfileQuery.PROJECTION,

                // Select only email addresses.
                ContactsContract.Contacts.Data.MIMETYPE + " = ?",
                new String[]{ContactsContract.CommonDataKinds.Email.CONTENT_ITEM_TYPE},

                // Show primary email addresses first. Note that there won't be
                // a primary email address if the user hasn't specified one.
                ContactsContract.Contacts.Data.IS_PRIMARY + " DESC");
    }

    @Override
    public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) {
        List<String> emails = new ArrayList<String>();
        cursor.moveToFirst();
        while (!cursor.isAfterLast()) {
            emails.add(cursor.getString(ProfileQuery.ADDRESS));
            // Potentially filter on ProfileQuery.IS_PRIMARY
            cursor.moveToNext();
        }

        ...
    }

    @Override
    public void onLoaderReset(Loader<Cursor> cursorLoader) {
    }

    private interface ProfileQuery {
        String[] PROJECTION = {
                ContactsContract.CommonDataKinds.Email.ADDRESS,
                ContactsContract.CommonDataKinds.Email.IS_PRIMARY,
        };

        int ADDRESS = 0;
        int IS_PRIMARY = 1;
    }
}

这需要READ_PROFILE和READ_CONTACTS权限:

<uses-permission android:name="android.permission.READ_PROFILE" />
<uses-permission android:name="android.permission.READ_CONTACTS" />

可悲的是，接受的答案并不管用。

我迟到了，但这是内部Android电子邮件应用程序的解决方案，除非内容uri由提供商更改:

Uri EMAIL_ACCOUNTS_DATABASE_CONTENT_URI = 
              Uri.parse("content://com.android.email.provider/account");

public ArrayList<String> GET_EMAIL_ADDRESSES ()
{
    ArrayList<String> names = new ArrayList<String>();
    ContentResolver cr      = m_context.getContentResolver();
    Cursor cursor           = cr.query(EMAIL_ACCOUNTS_DATABASE_CONTENT_URI ,null, 
                             null, null, null);

    if (cursor == null) {
        Log.e("TEST", "Cannot access email accounts database");
        return null;
    }

    if (cursor.getCount() <= 0) {
        Log.e("TEST", "No accounts");
        return null;
    }

    while (cursor.moveToNext()) {
        names.add(cursor.getString(cursor.getColumnIndex("emailAddress")));
        Log.i("TEST", cursor.getString(cursor.getColumnIndex("emailAddress")));
    }
    return names;
}

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 > 1)
            return parts[0];
    }
    return null;
}