ios - 为什么这个循环在这段代码之前执行？

Question

为什么 for 循环在 firebase 代码之前执行，即使它是在 firebase 代码之后输入的？

messageDB.observe(.childAdded) { (snapshot) in
    let snapshotValue = snapshot.value as! Dictionary<String,String>
    print("Snapshot value \(snapshotValue)")
    let email = snapshotValue["UserEmail"]!
    if (email == Auth.auth().currentUser?.email as String?){
        let user : UserString = UserString()
        user.name = snapshotValue["UserName"]!
        user.height = snapshotValue["UserHeight"]!
        user.weight = snapshotValue["UserWeight"]!
        user.date = snapshotValue["EntryDate"]!
        userArray.append(user)
    }    
}

for index in 0...4{
    print(index)
}  

Answer 1

这是因为 firebase observe 事件是 asynchronous , 所以如果你想在这之后执行一段代码，你需要把它移到 block 中。

所以你的代码将是:

messageDB.observe(.childAdded) { (snapshot) in
        let snapshotValue = snapshot.value as! Dictionary<String,String>
        print("Snapshot value \(snapshotValue)")
        let email = snapshotValue["UserEmail"]!
        if (email == Auth.auth().currentUser?.email as String?){
            let user : UserString = UserString()
            user.name = snapshotValue["UserName"]!
            user.height = snapshotValue["UserHeight"]!
            user.weight = snapshotValue["UserWeight"]!
            user.date = snapshotValue["EntryDate"]!
            userArray.append(user)
        }
        for index in 0...4{
           print(index)
        }
        // self.afterBlock()
    }

// func afterBlock() { yourCodeHere }

或者像在注释代码中那样在单独的方法中调用它。

别忘了remove当您关闭 ViewController 时观察。