add a preview if longpressing preview

lib/api/api.dart

@@ -3,12 +3,10 @@ import 'dart:convert';
 
 import 'package:http/http.dart' as http;
 import 'package:openmediacentermobile/api/token.dart';
-import 'package:openmediacentermobile/log/log.dart';
 
 class API {
   static Future<String> query(
       String apinode, String action, Object payload) async {
-    final Completer<String> cmpl = Completer();
     final t = await Token.getInstance().getToken();
     if (t != null) {
       final resp = await http.post(
@@ -20,11 +18,9 @@ class API {
         body: jsonEncode(payload),
       );
 
-      cmpl.complete(resp.body);
+      return resp.body;
     } else {
-      cmpl.complete("");
+      return "";
     }
-
-    return cmpl.future;
   }
 }