我正在尝试创建一个函数,该函数在Firebase中获取给定用户UID的类别子项的键,将它们附加到数组中,然后最终将它们连接在一起成为一个长字符串。一切操作都很好,直到observeSingleEvent函数完成并且返回值为空。这是我的代码:
let referenceDatabase = FIRDatabase.database().reference()
func fetchBuddyInfo(category: String, buddyId: String) -> String {
var buddyInterestsArray = [String]()
var buddyInterests = String()
referenceDatabase.child("Users").child(buddyId).child(category).observeSingleEvent(of: .value, with: { (categorySnap) in
for categoryItems in categorySnap.children.allObjects as! [FIRDataSnapshot] {
buddyInterestsArray.append(categoryItems.key)
}
buddyInterests = buddyInterestsArray.joined(separator: ",")
})
return buddyInterests
}
我认为这与observeSingleEvent函数的嵌套范围有关,因为buddyInterests在运行该函数后似乎会丢失其值,但是我不知道如何提取该值。
最佳答案
问题observeSingleEvent(of:with:)
是异步操作,这意味着它可以在执行函数后稍后返回。这就是为什么在您的情况下,您总是得到一个空String作为返回值的原因
解
因此,在您的情况下,您可以创建如下的完成处理程序:
func fetchBuddyInfo(category: String, buddyId: String, completion: @escaping (String) -> ()) {
var buddyInterestsArray = [String]()
var buddyInterests = String()
referenceDatabase.child("Users").child(buddyId).child(category).observeSingleEvent(of: .value, with: { (categorySnap) in
for categoryItems in categorySnap.children.allObjects as! [FIRDataSnapshot] {
buddyInterestsArray.append(categoryItems.key)
}
buddyInterests = buddyInterestsArray.joined(separator: ",")
completion(buddyInterests)
})
}
然后像这样调用您的函数:
fetchBuddyInfo(category: categoryString, buddyId: buddyId) { (buddyInfoString) in
// do whatever you want with your buddyInfoString
}
关于arrays - swift-获取和附加Firebase值的函数返回一个空字符串,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/57541036/