this is a fairly simple question.
I am using a web service in my app, and the server returns a JSON string to communitcate with the app.
Here is an example response:
{
repsonse = {
message = "Message";
"response_id" = X;
};
}
Using objective-c I want to be able to get what "response_id" is but I am unsure on how to do this.
Here is my code:
NSMutableArray *json = [NSJSONSerialization JSONObjectWithData:jsonData options:0 error:nil];
// Get json value
NSLog(#"%#", json);
if([json[#"response"][#"response_id"] isEqualToString:#"1"]){
return YES;
}else{
return NO;
}
Each time the isStringEqualTo method returns false.
Could somebody help me?
Thanks,
Peter
You have two problems:
json needs to be declared as an NSDictionary, not NSMutableArray since the JSON root is a dictionary, not an array. And you get back an immutable dictionary, not a mutable one.
The JSON has a key of "repsonse", not "response".
Related
This is the code i have so far
// Parse data using NSJSONSerialization
NSError *error = nil;
NSArray *JsonArray = [NSJSONSerialization JSONObjectWithData:myData options:NSJSONReadingMutableContainers error: &error];
if(!JsonArray)
{
NSLog(#"Error Parsing Data: %#", error);
}
else
{
for(NSDictionary *event in JsonArray)
{
if([[event description] isEqualToString:#"error"])
{
// Get error number? I am confused by this part
NSLog(#"Element: %#", [event objectForKey:#"error"]);
}
else
{
NSLog(#"Element: %#", [event description]);
}
}
}
this is the JSON Data that parses correctly:
[{data string}, {data strings}]
This only gives me the string "error" and not the int as well:
{"error":0}
I am echoing this data from a PHP script if that helps any. Am i just doing it wrong, or did i miss something?
Your problem is that when you receive an error, you get back an NSDictionary and not an NSArray. This should work:
if ([jsonObject isKindOfClass:[NSArray class]]) {
// no error: enumerate objects as you described above
} else if ([jsonObject isKindOfClass:[NSDictionary class]]) {
// error: obtain error code
NSNumber *errCode = jsonObject[#"error"];
} else {
// something bad's happening
}
Stylistic pieces of advice:
Don't call your object JsonArray, since it's not always an array. Call it jsonObject.
Don't start variable names with capital letters.
Would be great if you had posted the complete JSON document that you are trying to parse, because without that, there is absolutely no chance to figure out whether your code is anywhere near correct. The example [{data string}, {data strings}] that you gave is most definitely not a correct JSON document, so trying to parse it will return nil. {"error":0} is a dictionary with a single key "error" and a value 0. Having dictionaries with a single key is let's say unusual.
A JSON document contains either an array or object (using JSON terms) which will be turned either into an NSArray* or an NSDictionary*. You should know whether you expect an array or dictionary. If you expect an NSArray, check that [jsonObject isKindOfClass:[NSArray class]]. If you expect an NSDictionary, check that [jsonObject isKindOfClass:[NSDictionary class]]. If you don't do that then the wrong JSON document will either crash your app or produce total nonsense.
If you have an array then you will usually iterate through the elements of the array and handle each one in turn. If you have a dictionary you will usually look up keys that you know how to handle. What you are doing, iterating through an array of dictionaries, and checking for a dictionary with a key of "error", that's a very strange design of your JSON document.
And lookup what the "description" method does. "description" is what NSLog calls to find out what to print when it is asked to print an object. For an NSDictionary with a single key "error" and a value 0, it would return something like "error:0" which is of course not the same as "error".
NSDictionary *jsonDic = [NSJSONSerialization JSONObjectWithData:myData options:NSJSONReadingMutableContainers error:&error];
NSLog(#"jsonDic: %#", [jsonDic objectForKey:#"string"]);
I use the following code to get a NSString from a NSDictionary and then cast it into NSUrl:
NSURL * url = [NSURL URLWithString:[self.item objectForKey:#"website"]];
The NSDictionary self.item comes from a web server and it's correctly filled using JSON data. All the other objects inside the NSDictionary work perfectly fine.
But sometimes the web server passes a website url with the text "null" because the object has no website filled in. From debugging i learned that the NSURL object can contain a url with the text "null". But how do i prevent this, or how can i write an if statement that checks this?
I tried the following:
NSString * niks = [eventUrl absoluteString];
if(niks == #"null")
{
UIAlertView *message = [[UIAlertView alloc] initWithTitle:#"Event" message:#"Event heeft geen website" delegate:nil cancelButtonTitle:#"Oke" otherButtonTitles:#"Oke", nil];
[message show];
}
else
{
[webView loadRequest:[NSURLRequest requestWithURL:eventUrl]];
NSLog(#"%#",eventUrl);
}
But this doesn't work, it always passes the url directly to the webview. Can someone set me in the right direction?
Your comparison;
if(niks == #"null")
only compares if the pointers are equal (i.e. if the two are the same string object instance). Since one is a constant and the other is created dynamically from JSON fetched from the server, it's very unlikely.
To compare the content of two strings, you should instead do;
if([niks isEqualToString:#"null"])
For the link thirsty, here is the [NSString isEqualToString:] documentation.
To do string comparison, you need to do [niks isEqualToString:#"null"], that's why the first condition is broken.
You can also use [niks RangeOfString:#"null"];
I believe you can do this:
id str = [self.item objectForKey:#"website"];
if([str isMemberOfClass[NSNull class]]) {
... its null
}
The JSON convertors all change null to a NSNull object (in my experience).
I am not 100% clear of my memory, but I encountered a situation where [NSDictionary objectForKey:] actually returned NSNull class instance instead of "null" string.
If this is the case, you can check the class of [self.item objectForKey:#"website"] by using isKindOfClass method.
I'm learning Xcode at the moment and i have a project that is pulling data from a Mysql database using php and passing it to my app via json. In the database all varchars are set to utf8_bin.
here is the php:
header('Cache-Control: no-cache, must-revalidate');
header('Content-type: application/json');
echo json_encode($this->Idea_model->get($id));
here is a snipet of the outputted JSON:
[{"id":"1","title":"JWT blood sucka","objective":"test ","mission":"test","design_time":"80","development_time":"80","votes":"0","user_id":"0","date_created":"2012-08-03","date_modified":"2012-08-03","active":"1"},{"id":"2","title":"ford - liveDealer","objective":"to increce ","mission":"thid id a es","design_time":"80","development_time":"80","votes":"1","user_id":"1","date_created":"0000-00-00","date_modified":"0000-00-00","active":"1"}]
in xcode I'm using this function to pull in the JSON [reference tutorial:
http://www.raywenderlich.com/5492/working-with-json-in-ios-5]
(void)fetchedData:(NSData *)responseData {
//parse out the json data
NSError* error;
NSDictionary* json = [NSJSONSerialization
JSONObjectWithData:responseData //1
options:kNilOptions
error:&error];
NSArray* latestLoans = [json objectForKey:#"loans"]; //2
NSLog(#"loans: %#", latestLoans); //3
}
when i use this JSON file from the tutorial it works
http://api.kivaws.org/v1/loans/search.json?status=fundraising
but when i use my JSON file i get the following error.
[8690:207] -[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0x6a10400
Current language: auto; currently objective-c
obviously there is an issue with my JSON output as i printed the contents from the tutorial file in my PHP file and that worked as well.
i also have tried "reset contents and settings" in the iOS simulator.
any ideas?
The returned object appears to be an array but your code is treating it like a dictionary (json object/hash)
The error tells you this: it say that the message objectForKey: (which is a method on NSDictionary) is being sent to an instance of __NSCFArray, which is an implementation class of NSArray, hence my supposition...
Yes I have an Idea -
-[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0x6a10400
Arrays are not dictionaries. They do not respond to objectForKey
They respond to objectForIndex;
You are thinking you have an array when you have a dictionary.
Common JSON mistake.
Heres your data:
its a list
starts here --> "[" then the object starts here "{"
[{"id":"1","title":"JWT blood sucka","objective":"test ","mission":"test","design_time":"80","development_time":"80","votes":"0","user_id":"0","date_created":"2012-08-03","date_modified":"2012-08-03","active":"1"}
then a comma "," then the next item in the list starting with a { "{"id":"2","title":"ford - liveDea
JSON says a list is an array and an object is a dictionary so flip your code around
(void)fetchedData:(NSData *)responseData {
//parse out the json data
NSError* error;
NSArray* latestLoans = [NSJSONSerialization
JSONObjectWithData:responseData //1
options:kNilOptions
error:&error];
NSLog(#"loans: %#", latestLoans); //3
for (int i=0; i < latestLoans.count; i++)
{
NSDictionary *myLoan = (NSDictionary*)[latestLoans objectAtIndex:i];
NSLog(#"loan:%#", myLoan);
}
....
Got it?
I am new to Facebook Developer. I want to create Mac OSX application using Facebook API. When i request FQL and its return me JSON data only like below:
My Code:
[self.result_text setString:[NSString stringWithFormat:#"%#",[result objectForKey: #"result"]];
It display:
[{"name":"My Name","first_name":"My First Name","last_name":"My Last Name"}]
I want to read the object inside this Dictionary. Example I just want to display "My Name" string. But I don't know how to it.
Thanks,
As Ashley Mills wrote, you should check the documentation. You can loop through the all dictionary keys like this:
for ( NSString *key in [dictionary allKeys]) {
//do what you want to do with items
NSLog(#"%#", [dictionary objectForKey:key]);
}
Hope it helps
You can parse the JSON contents from the server into a NSDictionary object via Lion's brand new NSJSONSerialization class (documentation linked for you).
e.g.
NSDictionary *jsonDictionary = [NSJSONSerialization JSONObjectWithData: [self.result_text dataUsingEncoding: NSUTF8StringEncoding] options: nil error: &error];
And once you have it in a NSDictionary object, it's easy to do something like:
NSString * myLastNameContent = [jsonDictionary objectForKey: #"last_name"];
Sergio's answer (which he keeps editing, even as I type :-) is very good too. +1 to him.
You can use JSONKit to transform the JSON string into a dictionary:
NSDictionary *resultsDictionary = [resultString
objectFromJSONStringWithParseOptions:JKParseOptionLooseUnicode|JKParseOptionValidFlags error:&err];
NSString* name = [resultDictionary objectForKey:#"name"];
JSONKit is straightforward to use and will make your application work also on older SDK versions.
You should read the documentation for NSDictionary here:
https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/nsdictionary_Class/Reference/Reference.html
in particular the section titled Accessing Keys and Values
i have a problem using dataWithContentsOfURL.
I'm loading some images from the internet in a loop.
The Problem is: if the image at the URL doesn't exist, dataWithContentsOfURL does NOT return nil as expected. The apple reference says it returns nil if NSData could not be created.
Here's the Code:
NSString *TermineImgFileName = nil;
NSString *TermineImgPath = nil;
NSURL *TermineImgURL = nil;
NSData *TermineImg = nil;
for (deviceTermineHighInt; deviceTermineHighInt <= serverTermineHighInt; deviceTermineHighInt++) {
TermineImgFileName = [NSString stringWithFormat:#"Termine%i.png", deviceTermineHighInt];
TermineImgURL = [rootURL URLByAppendingPathComponent:TermineImgFileName];
TermineImg = [NSData dataWithContentsOfURL:TermineImgURL];
if (TermineImg != nil) {
TermineImgPath = [[paths objectAtIndex:0] stringByAppendingPathComponent:TermineImgFileName];
[TermineImg writeToFile:TermineImgPath atomically:YES];
updateCount += 1;
NSLog(#"File %# saved", TermineImgFileName);
}
else {
NSLog(#"Write Error");
}
TermineImg = nil;
}
Do you know why the method doesn't return nil if the file at the URL doesn't exist?
And a second question: Does it make sense to use the Strings, NSURL and NSData as i did? I thought for memory reasons it would be the best way.
Thank you in advance,
Nikos
Edit: The variables for the loop are defined before the code, the loop works fine. Also the variable rootURL is a constant defined in the header. The URL is built fine and it works.
I'd say the question is what the server actually does if you request a non-existing image.
If it gives you a 404, -dataWithContentsOfURL: should return nil - but if it doesn't, a NSData instance with the results will be created which just happens to not contain any useful image data.
Testing the code (on a single run ). If the image does not exist I get the Write Error as expected. Whats returned is (NULL). Which I think acts the same in this case, and points to a zero value.
There is a stackoverflow post which tries to explain it Here. are-null-and-nil-equivalent