通过访问令牌创建GoogleCredential

Question

private void retrieveNextPage(){

    if(mHasMore == false)
        return;

    Query query = new Query.Builder().setPageToken(mNextPageToken).build();
    com.google.android.gms.drive.Drive.DriveApi.query(getGoogleApiClient(), query).setResultCallback(metadataBufferResultResultCallback);

}

用户必须在浏览器和应用程序之间手动复制粘贴“授权码”，这在Android中不是一种实用的获取访问令牌的方法。

为了找到一种新的方法，我使用Android API中的GoogleAuthutil来获取访问令牌，同时使用Java API中的GoogleCredential和Drive来获取文件列表，如下所示，

private static List<File> retrieveFiles(Drive service) throws IOException{
    List<File> result = new ArrayList<File>();
    Files.List request = service.files().list();
    do {
        try{
            FileList fileList = request.execute();
            result.addAll(fileList.getItems());
            request.setPageToken(fileList.getNextPageToken());

        }catch (IOException e){
            Log.d(dbgT + "JavaRetrieveFiles", "Retrieved Failed");
            request.setPageToken(null);
        }
    }while (request.getPageToken() != null && request.getPageToken().length() > 0);

    return result;
}

private class RetrieveTokenTask extends AsyncTask<String, Void, String>{

    @Override
    protected String doInBackground(String... params){
        String accountName = params[0];
        String scopes = "oauth2:" + "https://www.googleapis.com/auth/drive";
        String token = null;

        try{
            token = GoogleAuthUtil.getToken(getApplicationContext(), accountName, scopes);
        }
        catch (IOException e){
            Log.e(excpTAG, "IO Exception: " + e.getMessage());
        }
        catch (UserRecoverableAuthException e){
            startActivityForResult(e.getIntent(), REQ_SIGN_IN_REQUIRED);
        }
        catch (GoogleAuthException e)
        {
            Log.e(excpTAG, "GoogleAuthException: " + e.getMessage());
        }

        return token;
    }

    @Override
    protected void onPostExecute(String s){
        super.onPostExecute(s);

        //Get Access Token
        Log.d( dbgT + "Token", s);
        EditText tokenText = (EditText) findViewById(R.id.tokenText);
        tokenText.setText(s);

        EditText fileNameText = (EditText) findViewById(R.id.editTextMeta);

        GoogleCredential credential = new GoogleCredential().setAccessToken(s);
        HttpTransport httpTransport = new NetHttpTransport();
        JsonFactory jsonFactory = new JacksonFactory();
        Drive service = new Drive.Builder(httpTransport, jsonFactory, null).setHttpRequestInitializer(credential).build();

        List<File> fileList;
        try{
            fileList = retrieveFiles(service);
            for(int i=0; i< fileList.size(); i++)
                fileNameText.append(fileList.get(i).getTitle());
        }catch(IOException e){
            Log.d(dbgT + "RetrieveFileList", "IO Exception" );
        }

    }
}

不幸的是，当调用retrievefiles中的request.execute()时，应用程序总是由于NetworkOnMainThreadException而崩溃。

所以我的问题是，如何通过使用访问令牌而不是在setFromTokenResponse中应用授权代码来创建正确的GoogleCredential？

提前谢了。