小编Oma*_*any的帖子

提供者值来自父小部件。我可以在构建上下文下使用提供程序值。但是，我需要getHomeCampaigns函数中的提供程序值。我尝试定义局部变量并将它们分配给构建小部件后的提供程序值，但该函数声称这些变量是在 null 上调用的。我想它们是在提供者的构建上下文下设置之前使用的。

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  // Variables to be set inside the function and then used by the last widget
  User currentUser;
  String country;
  List<CampaignWidget> friendsCamps;
  List<CampaignWidget> featuredCamps;

  // Function that needs the provider values
  getHomeCampaigns() async {
    // Get all campaigns where their owner is in the list of friends for the current user
    QuerySnapshot friendsSnapshot = await Firestore.instance
        .collection('campaigns')
        .where('user.uid', whereIn: currentUser.friends) …