Develop Reference

System.Text.Json.JsonException: The JSON value could not be converted

I'm using Ubuntu and dotnet 3.1, running vscode's c# extension.
I need to create a List from a JSON file, my controller will do some calculations with this model List that I will pass to it
So, here is my code and the error I'm getting.
First, I thought my error was because at model my attributes were char and C#, for what I saw, cannot interpret double-quotes for char, it should be single quotes. Before losing time removing it, I just changed my type declarations to strings and it's the same error.
Can someone help me?
ElevadorModel
using System.Collections.Generic;
namespace Bla
{
public class ElevadorModel
{
public int andar { get; set; }
public string elevador { get; set; }
public string turno { get; set; }
}
}
Program.cs:
class Program
{
static void Main(string[] args)
{
var path = "../input.json";
string jsonString;
ElevadorModel elevadoresModel = new ElevadorModel();
jsonString = File.ReadAllText(path); //GetType().Name = String
Console.WriteLine(jsonString); //WORKS
elevadoresModel = JsonSerializer.Deserialize<ElevadorModel>(jsonString);
}
JSON:

Your input json has an array as the base token, whereas you're expecting an object. You need to change your deserialization to an array of objects.
var elevadoresModels = JsonSerializer.Deserialize<List<ElevadorModel>>(jsonString);
elevadoresModel = elavoresModels.First();

Your input JSON is an array of models, however you're trying to deserialize it to a single model.
var models = JsonSerializer.Deserialize<List<ElevadorModel>>(jsonString);

This is also a problem in Blazor-Client side. For those calling a single object
e.g ClassName = await Http.GetFromJsonAsync<ClassName>($"api/ClassName/{id}");
This will fail to Deserialize. Using the same System.Text.Json it can be done by:
List<ClassName> ListName = await Http.GetFromJsonAsync<List<ClassName>>($"api/ClassName/{id}");
You can use an array or a list. For some reason System.Text.Json, does not give errors and it is successfully able Deserialize.
To access your object, knowing that it is a single object use:
ListName[0].Property
In your case the latter solution is fine but with the path as the input.

In my case, I was pulling the JSON data to deserialize out of an HTTP response body. It looked like this:
var resp = await _client.GetAsync($"{endpoint}");
var respBody = await resp.Content.ReadAsStringAsync();
var listOfInstances = JsonSerializer.Deserialize<List<modelType>>(respBody);
And the error would show up. Upon further investigation, I found the respBody string had the JSON base object (an array) wrapped in double quotes...something like this:
"[{\"prop\":\"value\"},...]"
So I added
respBody = respBody.Trim('\"');
And the error changed! Now it was pointing to an invalid character '\'.
I changed that line to include
respBody = respBody.Trim('\"').Replace("\\", "");
and it began to deserialize perfectly.
For reference:
var resp = await _client.GetAsync($"{endpoint}");
var respBody = await resp.Content.ReadAsStringAsync();
respBody = respBody.Trim('\"').Replace("\\", "");
var listOfInstances = JsonSerializer.Deserialize<List<modelType>>(respBody);

Issue in Parsing Json image in C#

net C#. I am trying to parse Json from a webservice. I have done it with text but having a problem with parsing image. Here is the Url from where I m getting Json
http://collectionking.com/rest/view/items_in_collection.json?args=122
And this is My code to Parse it
using (var wc = new WebClient()) {
JavaScriptSerializer js = new JavaScriptSerializer();
var result = js.Deserialize<ck[]>(wc.DownloadString("http://collectionking.com/rest/view/items_in_collection.json args=122"));
foreach (var i in result) {
lblTitle.Text = i.node_title;
imgCk.ImageUrl = i.["main image"];
lblNid.Text = i.nid;
Any help would be great.
Thanks in advance.
PS: It returns the Title and Nid but not the Image.
My class is as follows:
public class ck
{
public string node_title;
public string main_image;
public string nid; }

Your problem is that you are setting ImageUrl to something like this <img typeof="foaf:Image" src="http://... and not an actual url. You will need to further parse main image and extract the url to show it correctly.
Edit
This was a though nut to crack because of the whitespace. The only solution I could find was to remove the whitespace before parsing the string. It's not a very nice solution but I couldn't find any other way using the built in classes. You might be able to solve it properly using JSON.Net or some other library though.
I also added a regular expression to extract the url for you, though there is no error checking what so ever here so you'll need to add that yourself.
using (var wc = new WebClient()) {
JavaScriptSerializer js = new JavaScriptSerializer();
var result = js.Deserialize<ck[]>(wc.DownloadString("http://collectionking.com/rest/view/items_in_collection.json?args=122").Replace("\"main image\":", "\"main_image\":")); // Replace the name "main image" with "main_image" to deserialize it properly, also fixed missing ? in url
foreach (var i in result) {
lblTitle.Text = i.node_title;
string realImageUrl = Regex.Match(i.main_image, #"src=""(.*?)""").Groups[1].Value; // Extract the value of the src-attribute to get the actual url, will throw an exception if there isn't a src-attribute
imgCk.ImageUrl = realImageUrl;
lblNid.Text = i.nid;
}
}

Try This
private static string ExtractImageFromTag(string tag)
{
int start = tag.IndexOf("src=\""),
end = tag.IndexOf("\"", start + 6);
return tag.Substring(start + 5, end - start - 5);
}
private static string ExtractTitleFromTag(string tag)
{
int start = tag.IndexOf(">"),
end = tag.IndexOf("<", start + 1);
return tag.Substring(start + 1, end - start - 1);
}
It may help

populating a dictionary with links via HtmlAgility & custom webclient

private void button1_Click(object sender, EventArgs e)
{
test();
}
public void test()
{
Dictionary<string, string> LnksDict = new Dictionary<string, string>();
using (SmartWebClient smwc = new SmartWebClient())
{
HtmlAgilityPack.HtmlDocument htmlDoc = new HtmlAgilityPack.HtmlDocument();
htmlDoc.LoadHtml(smwc.DownloadString("http://www.google.com/adplanner/static/top1000/"));
var links = htmlDoc.DocumentNode
.Descendants("a").Select(x => x.Attributes["href"]);
foreach (var link in htmlDoc.DocumentNode.SelectNodes("//a"))
{
var UrlVal= link.Attributes["href"].Value;
var name = UrlVal.Split('.')[1];
LnksDict.Add(name, UrlVal);
}
}
}
#region <<=========== SmWbCl ============>>
public class SmartWebClient : WebClient
{
private readonly int maxConcurentConnectionCount;
public SmartWebClient(int maxConcurentConnectionCount = 20)
{
this.maxConcurentConnectionCount = maxConcurentConnectionCount;
}
protected override WebRequest GetWebRequest(Uri address)
{
var httpWebRequest = (HttpWebRequest)base.GetWebRequest(address);
if (httpWebRequest == null)
{
return null;
}
if (maxConcurentConnectionCount != 0)
{
this.Proxy = null;
this.Encoding = Encoding.GetEncoding("UTF-8");
httpWebRequest.ServicePoint.ConnectionLimit = maxConcurentConnectionCount;
}
return httpWebRequest;
}
}
#endregion
in this code i am trying to build a list of urls to be used as autoComplete source later.
what i am doing wrong is notc onditioning on adding the parsed values into the dictionary .
i need to find a way to add domain name as the key, even if already exist,
so i would like to be able to make a condition :
if the key in this dictionary already exists, add collection index of current link to string.value of key as a suffix
or if you would like to suggest a different solution all together... i will be happy to see new example.
thanks

I think what you want, rather than a Dictionary<string, string>, is a Dictionary<string, HashSet<string>>. That way, you can build a list of URLs for each domain. Your code to add an item to the list would be:
var UrlVal= link.Attributes["href"].Value;
var name = UrlVal.Split('.')[1];
// get links for this host
HashSet hostLinksList;
if (!LnksDict.TryGetValue(name, out hostLinksList))
{
hostLinksList = new HashSet<string>();
LnksDict.Add(name, hostLinksList);
}
// add the URL to the list of links for this host
hostLinksList.Add(UrlVal);
The key here is that calling Add on a HashSet when the item is already there won't throw an exception. It just doesn't add it again and returns false to indicate that the item was already in the collection.
When you're done, you have a list of URLs for each host (domain), which you can then use for your auto completion.
By the way, your method of splitting out the host using Split('.') isn't going to work very well. It assumes domains of the form "www.example.com". If you run into, for example, "example.com" (without the "www"), you're going to get "com" for the name. Also, "www.example.com" is going to collide with "www.example.org" and "www.example.co.uk". You need a better way of identifying hosts.

JsonConvert - Can not assign string value to a string variable

public void FindCityName()
{
string url = "http://maps.google.com/maps/geo?q=39.920794,32.853902&output=json&oe=utf8&sensor=true&key=MYKEY";
var w = new WebClient();
Observable.FromEvent<DownloadStringCompletedEventArgs>(w, "DownloadStringCompleted").Subscribe(r =>
{
var deserialized = JsonConvert.DeserializeObject<RootObject>(r.EventArgs.Result);
string s = deserialized.Placemark[0].AddressDetails.Country.SubAdministrativeArea.Locality.LocalityName;
/// setCity() and City=s produce the same thing
setCity(s);
City = s;
//foreach (var item in deserialized.Placemark)
//{
// //MessageBox.Show(item.AddressDetails.Country.SubAdministrativeArea.Locality.LocalityName);
// City = (string)item.AddressDetails.Country.SubAdministrativeArea.Locality.LocalityName;
//}
//Problem here >>>>>
////MessageBox.Show(City);
});
w.DownloadStringAsync(new Uri(url));
}
Problem:
I am working on a windows phone 7 application and I need to find the "City Name" from GPS coordinates in order to move forward...
I found the code above on the internet and tried it. I can see the city name by using these codes(Message.Box(City) show exactly what I want, the city name). However, this line of code
deserialized.Placemark[0].AddressDetails.Country.SubAdministrativeArea.Locality.LocalityName;
which gives me the city name seems to give a volatile string value.
For example, I created a method which assigns the value of string variable "s" to the string field of my class, name City. If I try to get the City's content after calling FindCityName() method, I see that City's content is not updated.
Again, same thing happens then I call the code line under the comment "Problem here >>>>>" that MessageBox.Show(City) shows nothing new...
Can someone explain me the reason of my problem?

you put this question on my blog as well, but I will answer it here. I feel a bit responsible for putting up the sample code in the first place ;-)
I am going to assume the class containing your code looks like this:
public class MyClass
{
private void MyMethod()
{
FindCityName();
MessageBox.Show(City);
}
private void FindCityName()
{
// Code omitted - see your question
}
private string City;
}
There is nothing volatile about the string. Your problem is asynchronicity. If you look carefully you will see that I use an observable that fires when the DownloadStringCompleted is fired. The code inside Observable.Event is only called when the download is finished but that happens asynchronously. But what I assume you do is call the FindCityName method and then directly trying to access results like I show in the MyMethod method. That's like directly wanting the result after firing the request. The results are not in yet! It's like a web page downloading - it takes a while. You can fix that with a callback, something like this:
public class MyClass
{
private void MyMethod()
{
FindName();
}
public void FindCityName()
{
string url = "http://maps.google.com/maps/geo?q=39.920794,32.853902&output=json&oe=utf8&sensor=true&key=MYKEY";
var w = new WebClient();
Observable.FromEvent<DownloadStringCompletedEventArgs>(w, "DownloadStringCompleted").Subscribe(r =>
{
var deserialized = JsonConvert.DeserializeObject<RootObject>(r.EventArgs.Result);
City = deserialized.Placemark[0].AddressDetails.Country.SubAdministrativeArea.Locality.LocalityName;
DoneDownloading();
});
w.DownloadStringAsync(new Uri(url));
}
private string City;
private void DoneDownloading
{
MessageBox.Show(City);
}
}
Does that help?

I would recommend you to use this Google Map API
http://maps.googleapis.com/maps/api/geocode/json?latlng=39.920794,32.853902&sensor=true
And once you get JSON response in your request. You can parse easily with NEWTONSOFT for wp7
WebClient wc = new WebClient();
var json = (JObject)JsonConvert.DeserializeObject(wc.DownloadString(url));
var locality= json["results"]
.SelectMany(x => x["address_components"])
.FirstOrDefault(t => t["types"].First().ToString() == "locality");
var name = locality!=null ? locality["long_name"].ToString() : "";

storing JSON data in db

I'm trying to store data from fb wall into database.
My *.cs code
public ActionResult GetWall()
{
JSONObject wallData = helper.Get("/me/feed");
if (wallData != null)
{
var data = wallData.Dictionary["data"];
List<JSONObject> wallPosts = data.Array.ToList<JSONObject>();
ViewData["Wall"] = wallPosts;
}
return View("Index");
}
Which gets posts from fb wall.
And then I have an *.aspx file, which "breaks" my wallposts into pieces (objects) or whatever you like to call them.
foreach (Facebook.JSONObject wallItem in wallPosts)
{
string wallItemType = wallItem.Dictionary["type"].String;
//AND SO ON...
What i'm trying to say is that I can access to elements inside fb JSON.
Is there a way i can access to the JSON elements inside *.cs file.
Or is there a way I can store elements inside the *.aspx file to db?
And if its possible, I would like to know how. =)
Thanks for help

Don't use the SDK. Fetch the JSON Data using HttpWebRequest and then Deserialize it using System.Runtime.Serialization.Json.DataContractJsonSerializer. You just have to Create a class with same properties returned in JSON data. See the example below
string Response = Utilities.HttpUtility.Fetch("https://graph.facebook.com/me?access_token=" + AccessToken, "GET", string.Empty);
using (System.IO.MemoryStream oStream = new System.IO.MemoryStream(System.Text.Encoding.UTF8.GetBytes(Response)))
{
oStream.Position = 0;
return (Models.FacebookUser)new System.Runtime.Serialization.Json.DataContractJsonSerializer(typeof(Models.FacebookUser)).ReadObject(oStream);
}

I'm not familiar with the facebook API and the question isn't too clear, but I assume that the string wallItemType is itself a JSON string, and you wish to parse it.
I'd use the Json.Net library to parse this.
using Newtonsoft.Json;
//your code as above
foreach (Facebook.JSONObject wallItem in wallPosts)
{
string wallItemType = wallItem.Dictionary["type"].String;
//I assume wallItemType is a JSON string {"name":"foobar"} or similar
JObject o = JObject.Parse(wallItemType);
string name = (string)o["name"]; //returns 'foobar'
//and so on
you can also use the Json.Net to deserialize to a custom type. This custom type could be mapped to a SQL database using NHibernate.
If you wish to store the entire json string in a database, then you could use a document database such as CouchDB.