JSON with dict in Array - arrays

Question

I keep getting error since last week but I can finde the problem. Maybe you can help me out.
I have got this function:
func getAllBlocks () { //Abruf der JSON Daten zum Überblick.
let JSONurl = "https://chain.api.btc.com/v3/block/latest,5000,2" //URL festlegen
let url = URL(string: JSONurl ) //String umwandeln in eine URl
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in //Datenabruf
if error != nil {
print("ERROR \(String(describing: error))")
return
}
do {
let loadedJSON = try JSONSerialization.jsonObject(with: data!) as! [String:Any] //JSON verarbeiten
print(loadedJSON)
for (key, value) in loadedJSON {
print(key)
if (key == "data") { //prüfen auf key "data" und dann dessen Dict abgreifen
print("data")
XXXX
}}
} catch{ print("Error beim JSON decodieren! \(error)") }
}
task.resume()
}
So what it should do is: get these three blocks from the URL and get all the Data into array or a struct. What it does: as long as I am only loading the "latest" block it is fine. But wenn I am loading more than one Block there pops up an array that I am not able to handle.
The code is running to the last print statement but after that it crashers no matter how I try to get my data.
What am I doing wrong?
Thanks!

Answer 1

You can parse JSON using Swift Codable Protocol (available from Swift 4). For that, you need a create a struct, that has to conform to Codable Protocol. In this case, I've created two structs. "BitCoinData" to save data collection and error. "BitData" is to save properties inside the data collection.
Note that properties should be same as JSON response keys
Tested with the data in the following urls:
https://chain.api.btc.com/v3/block/5000,50001
https://chain.api.btc.com/v3/block/latest,5000,2
struct BitCoinData: Codable {
var data : [BitData]?
var err_no: Int?
var err_msg: String?
}
struct BitData: Codable {
var height: Int?
var version: Int?
var mrkl_root: String?
var timestamp: Int?
var bits : Int?
var nonce: Int?
var hash: String?
var prev_block_hash: String?
var next_block_hash: String?
var size: Int?
var pool_difficulty: Int?
var difficulty: Double?
var tx_count: Int?
var reward_block: Int?
var reward_fees: Int?
var created_at: Int?
var confirmations: Int?
var is_orphan: Bool?
var curr_max_timestamp: Int?
var is_sw_block: Bool?
var stripped_size: Int?
var weight: Int?
}
//JSONDecoder to parse the response.
do {
let decoder = JSONDecoder()
//Pass the class here to start decoding your JSON response with respect to your mapped class.
let gitData = try decoder.decode(BitCoinData.self, from: responseData)
print("JSON Response: \(gitData.data![0].height!)")
}
catch DecodingError.dataCorrupted{
print("Data Corrupted");
}
catch DecodingError.typeMismatch{
print("typeMismatch");
}
catch DecodingError.valueNotFound{
print("Value Not Found");
}
catch DecodingError.keyNotFound{
print("Key Not Found");
}
catch {
print("Unable to Parse");
}

Answer 2

I see one difference between responses with one object (https://chain.api.btc.com/v3/block/latest) and with several objects (https://chain.api.btc.com/v3/block/5000,50001). In the first case the data parameter is a Dictionary, in the second one it is an Array. Check the code, that is responsible for parsing the data parameter. In any case, it is vary bad practice to change the parameter type in the API depending on the number of objects.