如何使用NSJSONSerialization

Question

我有一个JSON字符串（来自PHP的json_encode()看起来像这样：

[{"id": "1", "name":"Aaa"}, {"id": "2", "name":"Bbb"}]

我想将其解析为我的iPhone应用程序的某种数据结构。我想对我来说最好的事情就是拥有一个字典数组，所以数组中的第0个元素是一个带有键"id" => "1"和"name" => "Aaa"的字典。

我不明白NSJSONSerialization如何存储数据。到目前为止，这是我的代码：

NSError *e = nil;
NSDictionary *JSON = [NSJSONSerialization 
    JSONObjectWithData: data 
    options: NSJSONReadingMutableContainers 
    error: &e];

这只是我在其他网站上看到的一个例子。我一直试图通过打印出这些元素和类似的东西来阅读JSON对象，但我总是得到EXC_BAD_ACCESS。

如何使用NSJSONSerialization解析上面的JSON，并将其转换为我提到的数据结构？

Answer 1

您的根json对象不是字典而是数组：

[{"id": "1", "name":"Aaa"}, {"id": "2", "name":"Bbb"}]

这可能会让您清楚地了解如何处理它：

NSError *e = nil;
NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData: data options: NSJSONReadingMutableContainers error: &e];

if (!jsonArray) {
  NSLog(@"Error parsing JSON: %@", e);
} else {
   for(NSDictionary *item in jsonArray) {
      NSLog(@"Item: %@", item);
   }
}

Answer 2

这是我检查收到的json是数组还是字典的代码：

NSError *jsonError = nil;
id jsonObject = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:&jsonError];

if ([jsonObject isKindOfClass:[NSArray class]]) {
    NSLog(@"its an array!");
    NSArray *jsonArray = (NSArray *)jsonObject;
    NSLog(@"jsonArray - %@",jsonArray);
}
else {
    NSLog(@"its probably a dictionary");
    NSDictionary *jsonDictionary = (NSDictionary *)jsonObject;
    NSLog(@"jsonDictionary - %@",jsonDictionary);
}

我已经尝试过这个选项：kNilOptions和NSJSONReadingMutableContainers，并且两者都能正常工作。

显然，在if-else块中创建NSArray或NSDictionary指针时，实际代码不能这样。

Answer 3

它对我有用。您的data对象可能是nil，并且正如rckoenes所指出的，根对象应该是（可变的）数组。看到这段代码：

NSString *jsonString = @"[{\"id\": \"1\", \"name\":\"Aaa\"}, {\"id\": \"2\", \"name\":\"Bbb\"}]";
NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
NSError *e = nil;
NSMutableArray *json = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&e];
NSLog(@"%@", json);

（我不得不使用反斜杠转义JSON字符串中的引号。）

Answer 4

您的代码似乎没问题，但结果是NSArray，而不是NSDictionary，这是一个示例：

前两行只是用JSON创建一个数据对象，就像你从网上读取它一样。

NSString *jsonString = @"[{\"id\": \"1\", \"name\":\"Aaa\"}, {\"id\": \"2\", \"name\":\"Bbb\"}]";
NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];

NSError *e;
NSMutableArray *jsonList = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&e];
NSLog(@"jsonList: %@", jsonList);

NSLog内容（词典列表）：

jsonList: (
           {
               id = 1;
               name = Aaa;
           },
           {
               id = 2;
               name = Bbb;
           }
           )

Answer 5

[{"id": "1", "name":"Aaa"}, {"id": "2", "name":"Bbb"}]

在上面的JSON数据中，您显示我们有一个包含字典数的数组。

您需要使用此代码进行解析：

NSError *e = nil;
NSArray *JSONarray = [NSJSONSerialization JSONObjectWithData: data options: NSJSONReadingMutableContainers error: &e];
        for(int i=0;i<[JSONarray count];i++)
        {
            NSLog(@"%@",[[JSONarray objectAtIndex:i]objectForKey:@"id"]);
             NSLog(@"%@",[[JSONarray objectAtIndex:i]objectForKey:@"name"]);
        }

对于swift 3/3 +

   //Pass The response data & get the Array
    let jsonData = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as! [AnyObject]
    print(jsonData)
    // considering we are going to get array of dictionary from url

    for  item  in jsonData {
        let dictInfo = item as! [String:AnyObject]
        print(dictInfo["id"])
        print(dictInfo["name"])
    }

Answer 6

以下代码从Web服务器获取JSON对象，并将其解析为NSDictionary。我使用了openweathermap API，它为此示例返回一个简单的JSON响应。为了简单起见，此代码使用同步请求。

   NSString *urlString   = @"http://api.openweathermap.org/data/2.5/weather?q=London,uk"; // The Openweathermap JSON responder
   NSURL *url            = [[NSURL alloc]initWithString:urlString];
   NSURLRequest *request = [NSURLRequest requestWithURL:url];
   NSURLResponse *response;
   NSData *GETReply      = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
   NSDictionary *res     = [NSJSONSerialization JSONObjectWithData:GETReply options:NSJSONReadingMutableLeaves|| NSJSONReadingMutableContainers error:nil];
   Nslog(@"%@",res);

Answer 7

@rckoenes已经向您展示了如何从JSON字符串中正确获取数据。

对于您提出的问题：EXC_BAD_ACCESS几乎总是在您尝试访问[自动]释放后的对象时出现。这不是特定于JSON [de-]序列化，而是与您获取对象然后在它被释放后访问它有关。它通过JSON发布的事实并不重要。

有很多页面描述了如何调试这一点 - 您想要Google（或SO）obj-c zombie objects，特别是NSZombieEnabled，这对您来说非常有用，可帮助您确定你的僵尸对象的来源。 （“Zombie”是你释放一个对象时所调用的，但保留一个指针并稍后尝试引用它。）

Answer 8

使用do / try / catch块在Xcode 7（Beta）上使用Swift 2.0：

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form name="form1" id="form1">
  <input type="text" name="firstname" value="ABCD"/>
  <input type="text" name="lastname" value="XYZ"/>
</form>

Answer 9

注意：对于Swift 3 。 您的JSON字符串返回Array而不是Dictionary。请尝试以下内容：

        //Your JSON String to be parsed
        let jsonString = "[{\"id\": \"1\", \"name\":\"Aaa\"}, {\"id\": \"2\", \"name\":\"Bbb\"}]";

        //Converting Json String to NSData
        let data = jsonString.data(using: .utf8)

        do {

            //Parsing data & get the Array
            let jsonData = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as! [AnyObject]

            //Print the whole array object
            print(jsonData)

            //Get the first object of the Array
            let firstPerson = jsonData[0] as! [String:Any]

            //Looping the (key,value) of first object
            for (key, value) in firstPerson {
                //Print the (key,value)
                print("\(key) - \(value) ")
            }

        } catch let error as NSError {
            //Print the error
            print(error)
        }

Answer 10

#import "homeViewController.h"
#import "detailViewController.h"

@interface homeViewController ()

@end

@implementation homeViewController

- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.tableView.frame = CGRectMake(0, 20, 320, 548);
    self.title=@"Jason Assignment";

    // Uncomment the following line to preserve selection between presentations.
    // self.clearsSelectionOnViewWillAppear = NO;

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;
    [self clientServerCommunication];
}

-(void)clientServerCommunication
{
    NSURL *url = [NSURL URLWithString:@"http://182.72.122.106/iphonetest/getTheData.php"];
    NSURLRequest *req = [NSURLRequest requestWithURL:url];
    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:req delegate:self];
    if (connection)
    {
        webData = [[NSMutableData alloc]init];
    }
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [webData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [webData appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSDictionary *responseDict = [NSJSONSerialization JSONObjectWithData:webData options:0 error:nil];

    /*Third party API
     NSString *respStr = [[NSString alloc]initWithData:webData encoding:NSUTF8StringEncoding];
     SBJsonParser *objSBJson = [[SBJsonParser alloc]init];
     NSDictionary *responseDict = [objSBJson objectWithString:respStr]; */
    resultArray = [[NSArray alloc]initWithArray:[responseDict valueForKey:@"result"]];
    NSLog(@"resultArray: %@",resultArray);
    [self.tableView reloadData];
}


- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
//#warning Potentially incomplete method implementation.
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
//#warning Incomplete method implementation.
    // Return the number of rows in the section.
    return [resultArray count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
    }

    // Configure the cell...
    cell.textLabel.text = [[resultArray objectAtIndex:indexPath.row] valueForKey:@"name"];
    cell.detailTextLabel.text = [[resultArray objectAtIndex:indexPath.row] valueForKey:@"designation"];

    NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[[resultArray objectAtIndex:indexPath.row] valueForKey:@"image"]]];
cell.imageview.image = [UIImage imageWithData:imageData];

    return cell;
}

/*
// Override to support conditional editing of the table view.
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Return NO if you do not want the specified item to be editable.
    return YES;
}
*/

/*
// Override to support editing the table view.
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the row from the data source
        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
    }   
    else if (editingStyle == UITableViewCellEditingStyleInsert) {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
    }   
}
*/

/*
// Override to support rearranging the table view.
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath
{
}
*/

/*
// Override to support conditional rearranging of the table view.
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Return NO if you do not want the item to be re-orderable.
    return YES;
}
*/


#pragma mark - Table view delegate

// In a xib-based application, navigation from a table can be handled in -tableView:didSelectRowAtIndexPath:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Navigation logic may go here, for example:
     //Create the next view controller.
    detailViewController *detailViewController1 = [[detailViewController alloc]initWithNibName:@"detailViewController" bundle:nil];

 //detailViewController *detailViewController = [[detailViewController alloc] initWithNibName:@"detailViewController" bundle:nil];

 // Pass the selected object to the new view controller.

 // Push the view controller.
 detailViewController1.nextDict = [[NSDictionary alloc]initWithDictionary:[resultArray objectAtIndex:indexPath.row]];
 [self.navigationController pushViewController:detailViewController1 animated:YES];

    // Pass the selected object to the new view controller.

    // Push the view controller.
  //  [self.navigationController pushViewController:detailViewController animated:YES];
}



@end

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
    empName.text=[nextDict valueForKey:@"name"];
    deptlbl.text=[nextDict valueForKey:@"department"];
    designationLbl.text=[nextDict valueForKey:@"designation"];
    idLbl.text=[nextDict valueForKey:@"id"];
    salaryLbl.text=[nextDict valueForKey:@"salary"];
    NSString *ImageURL = [nextDict valueForKey:@"image"];
    NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:ImageURL]];
    image.image = [UIImage imageWithData:imageData];
}

Answer 11

问题似乎与对象的自动释放有关。 NSJSONSerialization JSONObjectWithData显然是创建一些自动释放的对象并将其传递给您。如果你试图把它带到另一个线程，它将无法工作，因为它不能在另一个线程上解除分配。

诡计可能是尝试做一个字典或数组的可变副本并使用它。

NSError *e = nil;
id jsonObject = [NSJSONSerialization 
JSONObjectWithData: data 
options: NSJSONReadingMutableContainers 
error: &e] mutableCopy];

将NSDictionary作为NSArray处理不会导致错误访问异常，但在进行方法调用时可能会崩溃。

另外，可能这里的选项并不重要但是最好给NSJSONReadingMutableContainers | NSJSONReadingMutableContainers | NSJSONReadingAllowFragments但即使它们是自动释放的对象，也可能无法解决此问题。

Answer 12

不好的例子，应该是这样的 {“ id”：1，“ name”：“某物”}

数字和字符串混合在一起。