将元素添加到来自For语句的Flutter中？

Question

我收到以下错误，同时试图从我的for循环元素添加到我的List ...

NoSuchMethodError: The method 'addAll' was called on null. 
    Receiver: null 
    Tried calling: addAll("LrWr826cd3Y") 

这里是我的代码...

Future getData() async { 
    //Map videoId; 

    String url = 'https://Youtube API'; 
    var httpClient = createHttpClient(); 
    var response = await httpClient.read(url); 
    Map data = JSON.decode(response); 
    var videos = data['items']; //returns a List of Maps 

    List searchTitles; 
    List searchIds; 
    List searchImages; 

    for (var items in videos) { 
     //iterate over the list 
     Map myMap = items; //store each map 
     final video = (myMap['id'] as Map); 
     print(video['videoId']); 
     searchIds.addAll(video['videoId']); 
     final details = (myMap['snippet'] as Map); 
     final videoimage = (details['thumbnails'] as Map); 
     final medium = (videoimage['medium'] as Map); 

    } 

    setState(() { }); 

    if (!mounted) return; 
    } 

print(video['videoId']);成功地列出了3 Youtube视频ID作为字符串。 searchIds.addAll(video['videoId']);引发错误。我试过searchIds.add和searchIds.addAll。我哪里错了？

我想这些名单最终推到我这里List类..

class CardInfo { 
    //Constructor 
    List id; 
    List title; 
    List video; 

    CardInfo.fromJson(List json) { 
    this.id; 
    this.title; 
    this.video; 
    } 
} 

Answer 1

你是不是你的实例化对象searchIds。添加这个

List searchIds = new ArrayList<>();