使用iOS中的objectForKey使用NSJSONSerialization类解析json

Question

I am new in iOS development. I use this code to connect to my REST Web Service and fetch data in Json format.

    NSString *url=@"URL_Address";

    NSURLRequest *theRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:url]];

    NSURLResponse *resp = nil;
    NSError *err = nil;

    NSData *response = [NSURLConnection sendSynchronousRequest: theRequest returningResponse: &resp error: &err];

//    NSString * theString = [[NSString alloc] initWithData:response encoding:NSUTF8StringEncoding]; 
//    NSLog(@"response: %@", theString);

    NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData: response options: NSJSONReadingMutableContainers error: &err];

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

Now I want to seperate them via objectForKey . I used this code inside the loop :

NSString *name = [item objectForKey:@"name"];

It does not work. I got this error:

2012-07-31 12:48:38.426 LearningAFNetworking[390:f803] -[__NSArrayM objectForKey:]: unrecognized selector sent to instance 0x6844460
2012-07-31 12:48:38.428 LearningAFNetworking[390:f803] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM objectForKey:]: unrecognized selector sent to instance 0x6844460'
*** First throw call stack:
(0x13c8022 0x1559cd6 0x13c9cbd 0x132eed0 0x132ecb2 0x2f40 0x2bf8 0xd9a1e 0x38401 0x38670 0x38836 0x3f72a 0x290b 0x10386 0x11274 0x20183 0x20c38 0x14634 0x12b2ef5 0x139c195 0x1300ff2 0x12ff8da 0x12fed84 0x12fec9b 0x10c65 0x12626 0x254d 0x24b5 0x1)
terminate called throwing an exception(lldb)

can you help me?

Answer 1

You have to access the 0 item of item array:

NSArray *mainArray = [item objectAtIndex:0];
(NSDictionary *obj in mainArray) {
     NSString *name = [obj objectForKey:@"name"];
}

When you got this error: -[__NSArrayM objectForKey:] , you need to realize that the object that you're trying to access isn't a dictionary. It's an array ( __NSArrayM ), so you have to first access the 0 index, and then starting exploring the dictionary.

Take a look at this amazing tutorial, from Ray Wenderlich, that explains everything about crashes.

Answer 2

As Alberto said, you assumed that item is an NSDictionary while in reality is an NSArray containing multiple dictionaries. Now for the drill-down part you can use valueForKeyPath as shown below. So your for loop should be something like this:

NSArray *items = [jsonArray objectAtIndex:0];

for (NSDictionary *item in items){
    NSString *name = [item valueForKey:@"name"];
    // You can also get nested properties like this
    NSString *projectName = [item valueForKeyPath:@"project.name"]; 
} 

Another useful thing to know is that if you'd like to get all 'name' values for example, you could use valueForKey on your items array, which would automatically call valueForKey on each dictionary for you. Example:

NSArray *items = [jsonArray objectAtIndex:0];
NSArray *names = [items valueForkey:@"name"];

Answer 3

From the error and from the log output of your code it looks like your are trying to execute the selector objectForKey on a NSArray . Try to change NSString *name = [item objectForKey:@"name"]; to NSString *name = [[item objectAtIndex: 0]objectForKey:@"name"];

Answer 4

这段代码可以帮助您从NSArray获取类型字典的第一个对象

[[jsonArray objectAtIndex:0]objectForKey:@"object-key"];

Answer 5

-(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];
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    custcell=[tableView dequeueReusableCellWithIdentifier:CellIdentifier];



    if(custcell==nil)
    {

        custcell=[[[NSBundle mainBundle]loadNibNamed:@"custumCell" owner:self options:nil]objectAtIndex:0];

    }


    custcell.persnName.text=[[arr objectAtIndex:indexPath.row]valueForKey:@"Name"];
    //else if (objsegment.selectedSegmentIndex==1)
    //{
    custcell.persnAge.text=[[arr objectAtIndex:indexPath.row]valueForKey:@"Age"];

    [sortcontrol addTarget:self action:@selector(SegmentbtnCLK:) forControlEvents:UIControlEventValueChanged];

    //objsegment.selectedSegmentIndex=0;
    // }

    return custcell;
}
- (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];
}
- (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];
}