无法将类型'Swift .__ SwiftDeferredNSArray'（0x104cd8ae8）的值强制转换为'NSMutableArray'（0x7fff87c52960）

Question

下面的代码行产生了错误，

let response1 : NSMutableArray = NSMutableArray.init(array: (JSON.object as! NSMutableArray).value(forKey: "media_list") as! NSArray)

正如错误所言，我理解其强制转换异常，但是我无法修改代码以使其正常工作。我是Swift的新手，所以我们将不胜感激。以下是我的JSON.object

所以，我检查了这是我的JSON.object

[["offset": 30119146, "file_size": 30119146, "filename": video_220120201129271580.mp4, "mediaPath": file:///Users/evuser/Library/Developer/CoreSimulator/Devices/B9B0232F-237D-4413-BB81-BD5FAC727305/data/Containers/Data/Application/401D5D91-4500-434A-98FE-BD416135A1C7/Documents/video_220120201129271580.mp4, "status": completed, "group_id": fKQ2Xd9bE0cXchsw, "createdDate": 2020/01/22 13:59:47, "_id": 5e27e4d3138c8801cd3c26ca, "user_id": 21, "mime_type": video/mp4, "dest_path": /video_220120201129271580.mp4, "resource_id": 3a743d84-eafe-41e5-9f4c-dece67598c32], 
["offset": 6435018, "file_size": 6435018, "filename": video_220120201127525480.mp4, "mediaPath": file:///Users/evuser/Library/Developer/CoreSimulator/Devices/B9B0232F-237D-4413-BB81-BD5FAC727305/data/Containers/Data/Application/401D5D91-4500-434A-98FE-BD416135A1C7/Documents/video_220120201127525480.mp4, "status": completed, "group_id": ffoHuGL0Z17vOqY9, "createdDate": 2020/01/22 13:58:10, "_id": 5e27e472138c8801cd3c26c9, "user_id": 21, "mime_type": video/mp4, "dest_path": /video_220120201127525480.mp4, "resource_id": 50e34fd5-b488-4861-aedd-03ea1ed0d91c]]

Answer 1

似乎JSON.object可能不是数组。或至少不是可变数组。如果不研究JSON.object，我们将很难识别您的问题。快速修复实际上可能是

let response1 : NSMutableArray = NSMutableArray.init(array: (JSON.object as! NSArray).value(forKey: "media_list") as! NSArray)

但是我会尝试进一步挖掘。尝试检查到底发生了什么，并避免使用旧的Objective-C下一步（NS）对象。逐步进行：

let response1: [Any]? = {
    guard let mainArray = JSON.object as? [Any] else {
        print("Outer object is not an array. Check type of \(JSON.object)")
        return nil
    }
    var mutableVersionOfArray = mainArray // This already creates a mutable copy because we used "var" instead of "let"
    guard let mediaList = mutableVersionOfArray.value(forKey: "media_list") as? [Any] else {
        print("Inner object is not an array. Check type of \(mutableVersionOfArray.value(forKey: "media_list"))")
        return nil
    }
    return mediaList    
}()

但是此代码对我来说毫无意义。查看您的代码，我希望您的JSON对象类似于：

{
    "media_list": [{}, {}]
}

在这种情况下，您正在查看词典。尝试以下操作：

let mediaList: [Any]? = {
    guard let topDictionary = JSON.object as? [String: Any] else {
        print("Outer object is not a dictionary. Check type of \(JSON.object)")
        return nil
    }
    guard let mediaListItem = topDictionary["media_list"] else {
        print("There is no media_list in payload")
        return nil
    }
    guard let mediaList = mediaListItem as? [Any] else {
        print("mediaList is not an array")
        return nil
    }
    return mediaList
}

我希望您能看到数组和字典之间的区别。数组中有N个有序元素，而字典中有键/值对。因此，要访问键下的值，可以将其称为dictionary[key]。您的整个代码（如果正确的话）可以是：

let response1 = (JSON.object as? [String: Any])?["media_list"] as? [Any]

但是如果返回nil，则可能很难调试出什么问题。

Answer 2

似乎JSON.object可能不是数组。或至少不是可变数组。如果不研究JSON.object，我们将很难识别您的问题。快速修复实际上可能是

let response1 : NSMutableArray = NSMutableArray.init(array: (JSON.object as! NSArray).value(forKey: "media_list") as! NSArray)

但是我会尝试进一步挖掘。尝试检查到底发生了什么，并避免使用旧的Objective-C下一步（NS）对象。逐步进行：

let response1: [Any]? = {
    guard let mainArray = JSON.object as? [Any] else {
        print("Outer object is not an array. Check type of \(JSON.object)")
        return nil
    }
    var mutableVersionOfArray = mainArray // This already creates a mutable copy because we used "var" instead of "let"
    guard let mediaList = mutableVersionOfArray.value(forKey: "media_list") as? [Any] else {
        print("Inner object is not an array. Check type of \(mutableVersionOfArray.value(forKey: "media_list"))")
        return nil
    }
    return mediaList    
}()

但是此代码对我来说毫无意义。查看您的代码，我希望您的JSON对象类似于：

{
    "media_list": [{}, {}]
}

在这种情况下，您正在查看词典。尝试以下操作：

let mediaList: [Any]? = {
    guard let topDictionary = JSON.object as? [String: Any] else {
        print("Outer object is not a dictionary. Check type of \(JSON.object)")
        return nil
    }
    guard let mediaListItem = topDictionary["media_list"] else {
        print("There is no media_list in payload")
        return nil
    }
    guard let mediaList = mediaListItem as? [Any] else {
        print("mediaList is not an array")
        return nil
    }
    return mediaList
}

我希望您能看到数组和字典之间的区别。数组中有N个有序元素，而字典中有键/值对。因此，要访问键下的值，可以将其称为dictionary[key]。您的整个代码（如果正确的话）可以是：

let response1 = (JSON.object as? [String: Any])?["media_list"] as? [Any]

但是如果返回nil，则可能很难调试出什么问题。