Flutter / Dart - How to convert complex objects to uri or query strings.

SimplifiedUri.dart

///A simple Flutter / Dart Utility class for converting complex objects to uri and query strings
///Sample usage on https://github.com/opatajoshua/SimplifiedUri
/*
final params = {
  'name': 'John',
  'columns': ['firstName', 'lastName'],
  'ageRange': {
    'from': 12,
    'to': 60,
  },
  'someInnerArray': [1,2,3,5]
};
final Uri uri = SimplifiedUri.uri('http://api.mysite.com/users', params);
final headers = {HttpHeaders.contentTypeHeader: 'application/json'};
final response = await http.get(uri, headers: headers);
*/
///by Joshua Opata. opatajoshua@gmail.com
class SimplifiedUri{
  static Uri uri(String url, dynamic param){
    // combine the url with the generated query string
    final urlString = "$url?${objectToQueryString(param)}";
    print('urlString: $urlString');
    //create a Uri object from the urlString and return
    return Uri.parse(urlString);
  }

  /// converts a dart object to a query string
  static String objectToQueryString(dynamic json){
    //if no param we return an empty string
    if(json==null)
      return "";
    //keep the list of parameters to transform
    List<String> queries = [];
    //lets handle map params
    if(json is Map){
      //we loop through all the map properties by their keys
      json.keys.forEach((key) {
        //if property value is a nested map we call our method that handles nested maps
        if(json[key] is Map){
          generateInnerMap(queries, "$key", json[key]);
        }
        //if value is an array we call our method that handles inner list
        else if(json[key] is List){
          generateInnerList(queries, "$key", json[key]);
        }
        //else we add the string conversion for the property. eg. name=joshua
        else
          queries.add("$key=${json[key]}");
      });
    }
    //lets handle list param by calling our method that handles inner list
    else if(json is List){
      generateInnerList(queries, "", json);
    }
    //lets join all transformed properties as a single string and urlEncode the string
    return  Uri.encodeFull(queries.join("&"));
  }

  ///transforms inner map properties and adds them to the query list
  static generateInnerMap(List<String> queryList, String parentKey,Map<String, dynamic> innerJson){
    //loop through each map key
    innerJson.keys.forEach((key) {
      // the property is another nested map we call recursive
      if(innerJson[key] is Map){
        generateInnerMap(queryList, "$parentKey[$key]", innerJson[key]);
      }
      // if the property is a list then we call the list transformer method
      else if(innerJson[key] is List){
        generateInnerList(queryList, "$parentKey[$key]", innerJson[key]);
      }
      // else we transform the primitive property and add to the query list. eg. ageRange[from]=3
      else
        queryList.add("$parentKey[$key]=${innerJson[key] }");
    });
  }

  ///transforms array properties and adds them to the query list
  static generateInnerList(List<String> queryList, String parentKey,List<dynamic> innerList){
    //loop through list items
    innerList.forEach((item) {
      //if property is a map object we call our map object transformer
      if(item is Map){
        generateInnerMap(queryList, "$parentKey[]", item as Map<String, dynamic>);
      }
      // else we transform the primitive property and add to the query list. eg. columns[]=firstName
      else
        queryList.add("$parentKey[]=$item");
    });
  }
}