Question

我正在从NSMutableDictionary生成一个JSON文档，该文档由指向NSStrings的键组成，以及两个指向其他NSMutableDictionary的键。我的问题是，当我输出JSON文档时，我注意到JSON文档具有以不同顺序插入NSMutableDictionary中的对象。例如，我目前的输出如下所示：

JSON Output: {
  "devicetype" : "iPhone Simulator",
  "os" : "6.0",
  "test_results" : [
    {
      "date" : "2012-12-25T20:38:09",
      "name" : "Test 1",
      "result" : "Fail"
    },
    {
      "date" : "2012-12-25T20:38:11",
      "name" : "Test 2",
      "result" : "Pass"
    },
    {
      "date" : "2012-12-25T20:38:13",
      "name" : "Test 3",
      "result" : "Pass"
    },
    {
      "date" : "2012-12-25T20:38:19",
      "name" : "Test 4",
      "result" : "Fail"
    }
  ],
  "devicename" : "?????",
  "reports" : [

  ],
  "device_id" : "bb88413b178b4ef77830d385b9a4bd6d",
  "platform" : "iPhone OS"
}

但我希望输出看起来像这样：

JSON Output: {
  "devicetype" : "iPhone Simulator",
  "os" : "6.0",
  "devicename" : "?????",
  "device_id" : "bb88413b178b4ef77830d385b9a4bd6d",
  "platform" : "iPhone OS"

  "test_results" : [
    {
      "date" : "2012-12-25T20:38:09",
      "name" : "Test 1",
      "result" : "Fail"
    },
    {
      "date" : "2012-12-25T20:38:11",
      "name" : "Test 2",
      "result" : "Pass"
    },
    {
      "date" : "2012-12-25T20:38:13",
      "name" : "Test 3",
      "result" : "Pass"
    },
    {
      "date" : "2012-12-25T20:38:19",
      "name" : "Test 4",
      "result" : "Fail"
    }
  ],

  "reports" : [

  ],
}

我创建JSON文档的代码如下所示：

NSMutableArray* reports = [NSMutableArray array];    
NSMutableArray* results = [NSMutableArray array];


for (TestResult *testObject in testResultArray) {

        if ([[DataModel sharedInstance] getScore:testObject.score] == @"Not Tested") {

            NSMutableDictionary *naTest = [NSMutableDictionary dictionary];
            [naTest setObject:testObject.testName forKey:@"name"];
            [naTest setObject:testObject.dateStamp forKey:@"date"];

            [reports addObject:naTest];

        }

        else {

            NSMutableDictionary *fullTest = [NSMutableDictionary dictionary];
            NSString *score = [[DataModel sharedInstance] getScore:testObject.score];
            [fullTest setObject:score forKey:@"result"];
            [fullTest setObject:testObject.testName forKey:@"name"];
            [fullTest setObject:testObject.dateStamp forKey:@"date"];


            [results addObject:fullTest];

        }

    }

    NSMutableDictionary *mainDoc = [NSMutableDictionary dictionary];
    [mainDoc setObject:udid forKey:@"device_id"];
    [mainDoc setObject:systemName forKey:@"platform"];
    [mainDoc setObject:systemVersion forKey:@"os"];
    [mainDoc setObject:@"?????" forKey:@"devicename"];
    [mainDoc setObject:deviceType forKey:@"devicetype"];

    [mainDoc setObject:results forKey:@"test_results"];
    [mainDoc setObject:reports forKey:@"reports"];


    NSError *ierror = nil;
    NSData *jsnData = [NSJSONSerialization dataWithJSONObject:mainDoc options:NSJSONWritingPrettyPrinted error:&ierror];
    NSString *jsnString = [[NSString alloc] initWithData:jsnData encoding:NSUTF8StringEncoding];
    NSLog(@"JSON Output: %@", jsnString);


}

我的另一个担心是test_results的输出也没有按照我想要的顺序出现。它们以“date”，“name”，“result”的顺序出现，我希望输出为“name”，“date”，“result”。有没有办法可以纠正这个顺序呢？

Answer 1

NSDictionary不提供有序的存储容器 - 您或许应该首先研究如何呈现数据，即直接查询字典键以对NSDictionary进行排序，以及将字典对象加载到NSArray中。

有很多关于NSDictionary缺乏“秩序”的信息。

这个SO问题提供了许多有用的解决方案，例如使用具有有序字典类的外部库，以及使用SortDescriptors： Is the Objective-C dictionary an ordered container?

Answer 2

NSDictionary不保证保持键/值对的顺序（并且它不应该因为NSDictionary不是数组，它是一个查找表）。如果你真的想要对它进行排序，最简单的方法是保持另一个数组，其内容是按照你想要的顺序存储的字典的键。当你解压缩JSON时，使用数组来查询字典。

需要生成的JSON文档与iOS中NSMutableDictionary中插入的对象的顺序相同

2 个答案: