Flutter从Future（布尔）返回bool类型。方法 [英] Flutter returning a bool type from a Future<bool> Method

问题描述

这个问题与

是否有一种方法可以从Future中获取布尔类型的返回类型

解决方案

从 doesNameAlreadyExist 返回的返回类型为 Future< bool> ; ，
所以行 doesNameAlreadyExist（ userName，usernameController.value）== true ，
实际上是 Future< bool> == bool 。
您需要等待，然后再等待结果。

  doesNameAlreadyExist（ userName，usernameController.value）。然后（值=>值== true）
  

或

 （等待dosNameAlreadyExist（ userName，usernameController.value））==真
  

在此处详细了解异步编程： Dart期货

This question is quite similar to this but the explanation didn't quite help for my use-case. I have a method of type Future that return a bool performing a query to cloud firestore to check if the username the user is entering already exists.

static Future<bool> doesNameAlreadyExist(String value, String 
name) async{
final QuerySnapshot result = await Firestore.instance
  .collection('users')
  .where(value, isEqualTo: name)
  .limit(1)
  .getDocuments();
  final List<DocumentSnapshot> documents = result.documents;
 return  documents.length == 1;

}

When i call that method here i get this error

Is there a way to get a return type of bool from a Future

解决方案

The return type returned from doesNameAlreadyExist is Future<bool>, so the line doesNameAlreadyExist("userName", usernameController.value) == true, is actually Future<bool> == bool. You need to await, or then the result.

doesNameAlreadyExist("userName", usernameController.value).then(value => value == true)

or

(await doesNameAlreadyExist("userName", usernameController.value)) == true

Read more about async programming here: Dart Futures

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