快速地，如何使函数从Firebase返回querysnapshot? [英] In swift, how to make function to return querysnapshot from Firebase?

问题描述

迅速，如何在此代码中返回 querySnapshot :

In swift, how can I return a the querySnapshot in this code:

  func read(){
    reference(to: .users).getDocuments() { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            for document in querySnapshot!.documents {
                print("\(document.documentID) => \(document.data())")

            }
        }

    }
}

上面的代码从firebase读取数据，并在else语句中打印出数据.我想从视图控制器调用 read()函数，并且 read()应该返回 querySnaphot！.documents .如果可以，我该怎么做:

The above code reads the data from firebase and prints the data out in the else statement. I want to call the read() function from a view controller and read() should return the querySnaphot!.documents. How can I do this if I do:

func read() -> QuerySnaphot{
...
return querySnapshot!.documents

它给我一个错误，它返回一个非空值

It gives me an error that it returns a non void value

推荐答案

void函数中意外的非void返回值

Unexpected non-void return value in void function

您不能在Clouser内部返回值.代替它，您可以使用完成处理程序.

You cannot return a value inside the clouser. Instead of it you can use completion handlers.

 func read(_ completion:@escaping(_ querySnapshot:[QueryDocumentSnapshot])->Void){
   reference(to: .users).getDocuments() { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {

            if let documents = querySnapshot?.documents{
                completion(documents)
            }
        }

    }

用法:

read { (documents) in

    for document in documents{

          print("\(document.documentID) => \(document.data())")
     }
}

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