我尝试将从Firebase检索到的数据保存到全局变量spendDict。但是，在我调用retrieveSpend（）之后，在关闭之外，spendDict仍然是空的。如何将Firebase的最终结果保存到Swift中的全局变量中。感谢。
该功能如下所示：
var spendDict: [String:[String]] = [:]
override func viewDidLoad() {
super.viewDidLoad()
retrieveSpend()
}
func retrieveSpend(){
// the dict will be [time:[amount , amount , amount]]
var spendDict :[String: [String]] = [:]
let spendDB = Database.database().reference().child("Spend")
spendDB.observe(.childAdded, with:{(snapshot) in
let returnValue = snapshot.value as! Dictionary<String, String>
var amount_retrieved = returnValue["amount"]
var time_retrieved = returnValue["time"]
var tag_retrieved = returnValue["tag"]
if self.spendDict.index(forKey: time_retrieved!) == nil {
// the key does not exist in the dictionary
self.spendDict[time_retrieved!] = [amount_retrieved!]
}
else{
self.spendDict[time_retrieved!]?.append(amount_retrieved!)
}
print("spendDict in closure ", spendDict)
})
print("spendDict outside the closure " , spendDict)
}
这是输出：
spendDict outside the closure [:]
spendDict in closure ["02-07-2018": ["7"]]
spendDict in closure ["02-07-2018": ["7"], "02-06-2018": ["6"]]
spendDict in closure ["02-05-2018": ["5"], "02-07-2018": ["7"], "02-06-2018": ["6"]]
spendDict in closure ["02-06-2018": ["6"], "02-08-2018": ["8"], "02-05-2018": ["5"], "02-07-2018": ["7"]]
spendDict in closure ["02-06-2018": ["6"], "02-08-2018": ["8"], "02-05-2018": ["5"], "02-07-2018": ["7"], "02-09-2018": ["9"]]
spendDict in closure ["02-01-2018": ["1"], "02-06-2018": ["6"], "02-08-2018": ["8"], "02-05-2018": ["5"], "02-07-2018": ["7"], "02-09-2018": ["9"]]
spendDict in closure ["02-09-2018": ["9"], "02-06-2018": ["6"], "02-02-2018": ["2"], "02-08-2018": ["8"], "02-01-2018": ["1"], "02-05-2018": ["5"], "02-07-2018": ["7"]]
spendDict in closure ["02-09-2018": ["9"], "02-03-2018": ["3"], "02-06-2018": ["6"], "02-02-2018": ["2"], "02-08-2018": ["8"], "02-01-2018": ["1"], "02-05-2018": ["5"], "02-07-2018": ["7"]]
spendDict in closure ["02-09-2018": ["9"], "02-03-2018": ["3"], "02-06-2018": ["6"], "02-02-2018": ["2"], "02-08-2018": ["8", "88"], "02-01-2018": ["1"], "02-05-2018": ["5"], "02-07-2018": ["7"]]
spendDict in closure ["02-09-2018": ["9"], "02-03-2018": ["3"], "02-06-2018": ["6"], "02-02-2018": ["2"], "02-10-2018": ["10"], "02-08-2018": ["8", "88"], "02-01-2018": ["1"], "02-05-2018": ["5"], "02-07-2018": ["7"]]