我有一个android应用程序，需要用户的许可才能访问它的谷歌电子表格（范围是谷歌电子表格API）。

在应用程序第一次发布时，一切正常，我可以很好地访问电子表格。我正在将用户选择的电子邮件地址保存到共享首选项中。

我想要的是，在用户下次启动应用程序时（第一次之后），应用程序将只获得令牌（因为我已经拥有用户的电子邮件地址），而用户不必再次通过帐户选择器。

我想这是以前做过的，因为用户应该只选择他的帐户一次。尽管如此，我不知道什么是最好的做法。

他是Google OAuth 2.0类

从这里直走http://developer.android.com/google/auth/http-auth.html

public class GoogleAccountActivity extends Activity {

    static final int REQUEST_CODE_PICK_ACCOUNT = 1000;
    static final int REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR = 1001;
    static final int REQUEST_CODE_RECOVER_FROM_AUTH_ERROR = 1002;

    String mEmail; 
    private static final String SCOPE =
            "oauth2:https://spreadsheets.google.com/feeds/";
    private Intent homeIntent;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        homeIntent=new Intent(this, HomeActivity.class); 
         // next activity tto launch
        pickUserAccount();
    }


    private void getUsername() {
        if (mEmail == null) {
            pickUserAccount();
        } else {
            if (isDeviceOnline()) {
                new GetUsernameTask(this, mEmail, SCOPE).execute();
            } else {
                Toast.makeText(this, R.string.not_online, Toast.LENGTH_LONG).show();
            }
        }
    }

    public boolean isDeviceOnline() {
        ConnectivityManager connMgr = (ConnectivityManager) 
            getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected()) {
            return true;
        } else {
            return false;
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_CODE_PICK_ACCOUNT) {
            // Receiving a result from the AccountPicker
            if (resultCode == RESULT_OK) {
                mEmail = data.getStringExtra(AccountManager.KEY_ACCOUNT_NAME);
                // With the account name acquired, go get the auth token
                getUsername();
            } else if (resultCode == RESULT_CANCELED) {
                // The account picker dialog closed without selecting an account.
                // Notify users that they must pick an account to proceed.
                Toast.makeText(this, R.string.pick_account, Toast.LENGTH_SHORT).show();
            }
        } else if ((requestCode == REQUEST_CODE_RECOVER_FROM_AUTH_ERROR ||
                requestCode == REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR)
                && resultCode == RESULT_OK) {
            // Receiving a result that follows a GoogleAuthException, try auth again
            getUsername();
        }
    }

    private void pickUserAccount() {
        String[] accountTypes = new String[]{"com.google"};
        Intent intent = AccountPicker.newChooseAccountIntent(null, null,
                accountTypes, false, null, null, null, null);
        startActivityForResult(intent, REQUEST_CODE_PICK_ACCOUNT);
    }



    public void handleException(final Exception e) {
        // Because this call comes from the AsyncTask, we must ensure that the following
        // code instead executes on the UI thread.
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                if (e instanceof GooglePlayServicesAvailabilityException) {
                    // The Google Play services APK is old, disabled, or not present.
                    // Show a dialog created by Google Play services that allows
                    // the user to update the APK
                    int statusCode = ((GooglePlayServicesAvailabilityException)e)
                            .getConnectionStatusCode();
                    Dialog dialog = GooglePlayServicesUtil.getErrorDialog(statusCode,
                            GoogleAccountActivity.this,
                            REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR);
                    dialog.show();
                } else if (e instanceof UserRecoverableAuthException) {
                    // Unable to authenticate, such as when the user has not yet granted
                    // the app access to the account, but the user can fix this.
                    // Forward the user to an activity in Google Play services.
                    Intent intent = ((UserRecoverableAuthException)e).getIntent();
                    startActivityForResult(intent,
                            REQUEST_CODE_RECOVER_FROM_PLAY_SERVICES_ERROR);
                }
            }
        });
    }

    public class GetUsernameTask extends AsyncTask<Void, Void, String>{
        Activity mActivity;
        String mScope;
        String mEmail;

        GetUsernameTask(Activity activity, String name, String scope) {
            this.mActivity = activity;
            this.mScope = scope;
            this.mEmail = name;
        }

        /**
         * Executes the asynchronous job. This runs when you call execute()
         * on the AsyncTask instance.
         */
        @Override
        protected String doInBackground(Void... params) {
            try {
                String token = fetchToken();
                if (token != null) {
                    homeIntent.putExtra("userToken", token);
                    startActivity(homeIntent); // starting the Home Activity
                }
            } catch (IOException e) {
                // The fetchToken() method handles Google-specific exceptions,
                // so this indicates something went wrong at a higher level.
                // TIP: Check for network connectivity before starting the AsyncTask.
            }
            return null;
        }

        /**
         * Gets an authentication token from Google and handles any
         * GoogleAuthException that may occur.
         */
        protected String fetchToken() throws IOException {
            try {
                return GoogleAuthUtil.getToken(mActivity, mEmail, mScope);
            } catch (UserRecoverableAuthException userRecoverableException) {
                // GooglePlayServices.apk is either old, disabled, or not present
                // so we need to show the user some UI in the activity to recover.
                handleException(userRecoverableException);
            } catch (GoogleAuthException fatalException) {
                // Some other type of unrecoverable exception has occurred.
                // Report and log the error as appropriate for your app.
            }
            return null;
        }
    }



}

它在第一次发布时运行良好，但我不确定下一次要做什么。

总而言之：

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