从Google Drive中列出文件，并在Android中获得所选文件的downloadUrl

Question

public class GoogleDriveActivity extends Activity {

private GoogleApiClient mGoogleApiClient;
public com.google.api.services.drive.Drive mService;
public GoogleAccountCredential credential;
public static final int REQUEST_AUTHORIZATION = 3;
public static final int REQUEST_ACCOUNT_PICKER = 4;

private static final String PREF_ACCOUNT_NAME = "accountName";
private static final String[] SCOPES = {DriveScopes.DRIVE_METADATA_READONLY};
final HttpTransport transport = AndroidHttp.newCompatibleTransport();
final JsonFactory jsonFactory = GsonFactory.getDefaultInstance();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_google_drive);

    SharedPreferences settings = getPreferences(Context.MODE_PRIVATE);
    credential = GoogleAccountCredential.usingOAuth2(
            getApplicationContext(), Arrays.asList(SCOPES))
            .setBackOff(new ExponentialBackOff())
            .setSelectedAccountName(settings.getString(PREF_ACCOUNT_NAME, "[e-mail]"));

    mService = new com.google.api.services.drive.Drive.Builder(
            transport, jsonFactory, credential)
            .setApplicationName("My Application")
            .build();
}

@Override
public void onResume() {
    super.onResume();
    refreshResults();
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    switch (requestCode) {
        case REQUEST_AUTHORIZATION:
            if (resultCode != RESULT_OK) {
                chooseAccount();
            }
            break;
        case REQUEST_ACCOUNT_PICKER:
            Log.w("gd", "in account picker");
            if (resultCode == RESULT_OK && data != null &&
                    data.getExtras() != null) {
                String accountName =
                        data.getStringExtra(AccountManager.KEY_ACCOUNT_NAME);
                if (accountName != null) {
                    credential.setSelectedAccountName(accountName);
                    SharedPreferences settings =
                            getPreferences(Context.MODE_PRIVATE);
                    SharedPreferences.Editor editor = settings.edit();
                    editor.putString(PREF_ACCOUNT_NAME, accountName);
                    editor.commit();
                }
            } else if (resultCode == RESULT_CANCELED) {
                Log.W("gd", "in cancelled");
            }
            break;

        default:
            super.onActivityResult(requestCode, resultCode, data);
            break;
    }
}

private void chooseAccount() {
    startActivityForResult(
            credential.newChooseAccountIntent(), REQUEST_ACCOUNT_PICKER);
}

private void refreshResults() {
    new GoogleDriveAsync(this).execute();
}

public class GoogleDriveAsync extends AsyncTask<Void, Void, Void> {

    private GoogleDriveActivity activity;

    @Override
    protected Void doInBackground(Void... voids) {
        try {
            getDataFromApi();

        } catch (final GooglePlayServicesAvailabilityIOException availabilityException) {
            Log.w("gd", "GPS unavailable");

        } catch (UserRecoverableAuthIOException userRecoverableException) {
            Log.w("gd", "user recoverable");
            activity.startActivityForResult(
                    userRecoverableException.getIntent(),
                    GoogleDriveActivity.REQUEST_AUTHORIZATION);

        } catch (Exception e) {
            Log.w("gd", "general exception " + e.getMessage());
        }
        return null;
    }

    GoogleDriveAsync(GoogleDriveActivity activity) {
        this.activity = activity;
    }

    /**
     * Fetch a list of up to 10 file names and IDs.
     *
     * @return List of Strings describing files, or an empty list if no files
     * found.
     * @throws IOException
     */
    private List<String> getDataFromApi() throws IOException {
        // Get a list of up to 10 files.
        List<String> fileInfo = new ArrayList<String>();
        FileList result = activity.mService.files().list()
                .setMaxResults(10)
                .execute();
        List<File> files = result.getItems();
        if (files != null) {
            for (File file : files) {
                fileInfo.add(String.format("%s (%s) (%s)\n",
                        file.getTitle(), file.getId(), file.getDownloadUrl()));
            }
        }
        Log.w("gd", "file info is " + fileInfo.toString());
        return fileInfo;

    }
}
}

Answer 1

        DriveId driveId = metadata.getDriveId();
        String resourceId = driveId.getResourceId();