Unable to Parse JSON Files on Swift3

I'm getting JSON from my API server and trying to log it.

let json:NSDictionary=try JSONSerialization.jsonObject(with:data!,options:.allowFragments)as!NSDictionary

in the section

The data couldn't be read because it is not in the correct format.

I get an error saying, but what is the cause of> From the contents of the session risp variable, I think the API access was successful with status code=200

SWIFT Code

func someTask(){
        let url = URL (string: "My API Address")!
        let session = URLSession(configuration:URLSessionConfiguration.default)
        let task = session.dataTask(with:url, completionHandler:{
            (data, resp, error) in

            if error!=nil{
                letstr=NSString(data:data!, encoding:String.Encoding.utf8.rawValue)
                print(str!)

                print(error!.localizedDescription)
                return
            }

            do{

                let json:NSDictionary=try JSONSERIALIZATION.jsonObject(with:data!,options:.allowFragments)as!NSDictionary

                print(json["a"]???"a:none")
                print(json["b"]???"b:none")

            } catchlet error as NSError {
                print(error.localizedDescription)
            }

        })
        task.resume()
    }

Code of your own API

<html>
<head>
</head>
<body>

<?php

$returnValue=array("a"=>1,"b"=>2);
echo json_encode($returnValue);

?>

</body>
</html>

swift swift3

2022-09-30 21:19

1 Answers

Your homegrown API code returns a byte string equivalent to the following string:

<html>
<head>
</head>
<body>

{"a":1, "b":2}

</body>
</html>

JSON responses buried in HTML tags like this cannot be parsed in JSONSERIALIZATION.

Try changing the server-side code as follows:

<?php

$returnValue=array("a"=>1,"b"=>2);
echo json_encode($returnValue);

I would like to recommend some modifications to Swift's code, so I will list them in bullet points.

(There should be no fatal impact on this issue, so you can ignore the following.)

data in case of error could be nil, so data! could crash the app
You do not need to use NSString to string a response in case of an error

str! is also dangerous

because the response to the error may not be interpreted by UTF-8

iflet data=data{
            let str = String (data:data, encoding: .utf8)
            print(str??"data not in UTF-8")
        } else{
            print("data is nil")
        }

If you expect the result to always be a JSON object (Dictionary on Swift side), you do not need options:.allowFragments
Swift3 makes it easier to get into the habit of using Swift's Dictionary (or Array) than using NSDictionary (or Array).

as! causes the app to crash when a non-JSON object response arrives

iflet json=try JSONSERIALIZATION.jsonObject(with:data!)as?[String:Any]{
            print(json["a"]???"a:none")
            print(json["b"]???"b:none")
        } else{
            print ("invalid JSON")
        }

str! is also dangerous

because the response to the error may not be interpreted by UTF-8

iflet data=data{
            let str = String (data:data, encoding: .utf8)
            print(str??"data not in UTF-8")
        } else{
            print("data is nil")
        }

If you expect the result to be a JSON object (Dictionary on Swift side), you do not need options:.allowFragments

as! causes the app to crash when a non-JSON object response arrives

iflet json=try JSONSERIALIZATION.jsonObject(with:data!)as?[String:Any]{
            print(json["a"]???"a:none")
            print(json["b"]???"b:none")
        } else{
            print ("invalid JSON")
        }

2022-09-30 21:19

If you have any answers or tips

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