将 Future<bool> 转换为 bool in flutter 以检查数据库是否存在

Question

我需要将 Future <bool> 转换为 bool。我知道可以用 then 和 await 来完成，但是怎么做呢？

class MyHomeApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {

    bool isLogin;
    checkDatabase().then((onValue){
      isLogin = onValue;
    });

    if(isLogin) return HomePageScreen();
    if(!isLogin) return SignInScreen();
  }

  Future<bool> checkDatabase() async{
    Directory directory = await getApplicationDocumentsDirectory();
    String path = directory.path + 'koca.db';
    return databaseExists(path);
  }
}

Answer 1

您可以使用 FutureBuilder :

class MyHomeApp extends StatelessWidget {

  Future<bool> get checkDatabase async {
    Directory directory = await getApplicationDocumentsDirectory();
    String path = directory.path + 'koca.db';
    return databaseExists(path);
  }

  @override
  Widget build(BuildContext context) =>
     FutureBuilder(
        future: checkDatabase,
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            if (snapshot.hasData) {
              if (snapshot.data) {
                return HomePageScreen();
              } else {
                return SignInScreen();
              }
            }
          }
          return Center(child: CircularProgressIndicator(),);
        },
      );
}

将 Future<bool> 转换为 bool in flutter 以检查数据库是否存在

Convert Future<bool> to bool in flutter to check if database exists or not

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flutter

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