Question

我有一个随机生成的数字数组，然后我尝试在Firebase中查询一个问题，该问题等于所选数字数组中索引[0]的值。目前的问题是我收到错误Cannot subscript a value of type '[UInt32]'。附：我在swift方面并不是极其有经验，因此精确的代码解决方案会非常苛刻！我还附上了我的火力架结构......

import UIKit
import Firebase

class QuestionViewController: UIViewController {


let ref = Firebase(url: "https://123test123.firebaseio.com/questions")

override func viewDidLoad() {
    super.viewDidLoad()

    // An empty array to hold the selected numbers
    var selectedNumbers: [UInt32] = []

    // A range of acceptable numbers
    let randomNumberRange = 1...10

    // How many numbers are needed?
    let randomNumbersToChoose = 10

    // Crash if asking for more numbers than are available in the range
    assert(randomNumberRange.count >= randomNumbersToChoose, "Must have enough numbers to choose from!")

    // Repeat this loop until all enough numbers have been selected
    while selectedNumbers.count < randomNumbersToChoose {

        // Pick a random number within the allowed range
        let selectedNumber = arc4random_uniform(UInt32(randomNumberRange.endIndex - randomNumberRange.startIndex)) + UInt32(randomNumberRange.startIndex)

        // If it's not already in the selected array, add it
        if (selectedNumbers.indexOf(selectedNumber) == nil) {
            selectedNumbers.append(selectedNumber)
        }
    }

    // Print the result
    print(selectedNumbers)


        print(selectedNumbers)
        let selectedNumberIndex: UInt32 = 2
        ref.queryOrderedByChild("value").queryEqualToValue(selectedNumbers[0])
            .observeEventType(.ChildAdded, withBlock: {
                snapshot in
                //Do something with the question
                print(snapshot.key)
                print(snapshot.value.valueForKey("question"))
            })
    }

@IBAction func truepressed(sender: AnyObject) {
}

@IBAction func falsePressed(sender: AnyObject) {
}

}

JSON数据：

{
  "question1" : {
    "answer" : "Nohghpe",
    "question" : "Do you know swift",
    "value" : 1
  },
  "question10" : {
    "answer" : "A fdsbit",
    "question" : "Do you kndfggow firebase",
    "value" : 10
  },
  "question2" : {
    "answer" : "A bfhit",
    "question" : "Dodhfg you know firebase",
    "value" : 2
  },
  "question3" : {
    "answer" : "A bsdit",
    "question" : "Do you know firebsgdfase",
    "value" : 3
  },
  "question4" : {
    "answer" : "A vcxbit",
    "question" : "Do yosgfdu know firebase",
    "value" : 4
  },
  "question5" : {
    "answer" : "A bivcxt",
    "question" : "Do you kfghnow firebase",
    "value" : 5
  },
  "question6" : {
    "answer" : "A bxcvit",
    "question" : "Do you know fnhirebase",
    "value" : 6
  },
  "question7" : {
    "answer" : "A bivxct",
    "question" : "Do you sgdfknow firebase",
    "value" : 7
  },
  "question8" : {
    "answer" : "A bivcxt",
    "question" : "Do you knsfdow firebase",
    "value" : 8
  },
  "question9" : {
    "answer" : "A bdsfit",
    "question" : "Do you kdfgnow ffsdirebase",
    "value" : 9
  }
}

Answer 1

这是Swift编译器模糊另一个背后的真实错误的典型情况。 .queryEqualToValue(..) method期望参数类型为AnyObject;它只能包含引用（类）类型，而UInt32是值类型。

另一个混乱的主题可能是我们通常习惯AnyObject类型可以，看似，持有Int类型的事实，实际上这样赋值隐式将Swift本机Int值类型转换为Foundation __NSCFNumber引用类型。但是，此隐式转换不适用于UInt32类型。

var a : AnyObject?
let foo : [Int] = [1, 2, 3]
let bar : [UInt32] = [1, 2, 3]

/* OK: Int -> [implicitly] -> __NSCFNumber */
a = foo[0]
print(a!.dynamicType) // __NSCFNumber

/* Not OK */
a = bar[0]
/* error: cannot subscript a value of type '[UInt32]' a = bar[0] */

因此，您可以通过以下方式解决此问题：

让selectedNumbers成为Int的数组，而不是UInt32（并相应地修改代码中受影响的部分）。
在您致电UInt32的通话中，执行从Int到.queryEqualToValue(..)的类型转换。例如，在上面的例子中：
```
a = Int(bar[0])
```
请注意，对于32位系统（例如iPhone 5），由UInt32类型表示的数字的上半部分的一半不能用Int类型表示，因为在32位系统上， Int对应Int32。
```
INT32_MAX   // 2147483647
UINT32_MAX  // 4294967295
```
但是，从快速浏览一下代码来看，这似乎不应该是一个问题，因为selectedNumbers的元素不会包含{{1}所代表的较大数字（对于64位系统：好的，UInt32对应Int）。但是，如果选择此选项，您应该在转换之前断言Int64值可以由用于运行应用程序的系统上的UInt32类型表示。

无法下标'[UInt32]'类型的值

1 个答案: