We Keep Coding

C# - Using reflection with JsonSchema4.FromTypeAsync

[INTRO]
I know there are about a zillion QA about generics and reflections everywhere, but it's becoming a blackhole to me, and I'm only getting more lost the more I read!!
What i need to do is simple, and I'm amazed that it hasn't been addressed before.
[SAMPLE] Consider the following snippit:
public async Task<string> generateJsonSchema(string model)
{
try
{
string modelName = "Models." + model;
Type t = Type.GetType(modelName, false);
JsonSchema4 schema = await JsonSchema4.FromTypeAsync<t>();
return schema.ToJson();
}
catch (Exception ex)
{
Logger.WriteToLogFile(ex.ToString(), "exception");
return "";
}
}
[PROBLEM] Now the main problem is that variable t is evaluated at runtime, thus, JsonSchema4.FromTypeAsync<t>() throws the error 't' is a variable but is used like a type when trying to build compile time
Whoever used JsonSchema4 will understand what I'm trying to achieve here.
Instead of creating a generate function for each of my models, or make a switch/if-else logic,
[QUESTION]
How to make it receive the model name as a string parameter, and convert the string-model-name to model-type and pass it to jSonSchema4 method.

The problem here is that, as you say, t is evaluated as runtime.
I also ran into this Problem and solved it by creating a MethodInfo of the method I wanted to invoke, in your case JsonSchema4.FromTypeAsync<t>().
So basically this is want may fix the problem:
var methodInfo = typeof(JsonSchema4).GetMethod("FromTypeAsync", new Type[] { }); //Get the "normal method info", the overload without parameters
var methodInfoWithType = methodInfo.MakeGenericMethod(t); //now you have a method with your desired parameter t as TypeParameter
Task<JsonSchema4> task = methodInfoWithType.Invoke(null, null) as Task<JsonSchema4>; //now you can cast the result from invoke as Task to keep the Async-Await functionality
var schema = await task;
return schema.ToJson();

Can't return HTTP status and data from a method after using httpClient.GetAsync()

I am having issues with the following code. I am retrieving a JSON object as a string and then wish to return this from my method so it can be used elsewhere. When I do however I get the message:
'filmsGlossary.searchQueries.returnJson(object); returns void, a return keyword must not be followed by an object expression'
public async void returnJson(object term)
{
//Set Variables
var searchFormat = "&format=json";
var termValue = term;
var httpClient = new HttpClient();
try
{
//Set web service URL format
string baseURI = "http://localhost/filmgloss/webService/web-service.php?termName=";
string userURI = baseURI + termValue + searchFormat;
//Send URL to web service and retrieve response code.
var response = await httpClient.GetAsync(userURI);
response.EnsureSuccessStatusCode();
var content = await response.Content.ReadAsStringAsync();
return content.ToString();
}
catch (HttpRequestException hre)
{
}
catch (Exception ex)
{
}
}
Originally I was only returning
return content;
However after reading it seemed that the issue might be that I needed to change this to:
return content.ToString();
However this did not help. I also read that I could change it to a synchronous, rather than asynchronous method and change the method to be 'public string' however I am only just learning c# and don't yet fully understand the implications of this (or how to do it).
Is it possible to resolve this error within the code I already have?
I would also like to understand the cause of the issue rather than just know the solution.
Thanks.

You really should paste the error messages that you are getting.
Why does your function declaration return void? It should return Task<string>.
public async Task<string> returnJson(object term)
Also in the body you should return the Task, like this:
await response.Content.ReadAsStringAsync();

HttpClient ReadAsAsync does not deserialize

I am not sure if the issue I am having is related to the way I'm using Task or if I am an not using ReadAsAsync correctly. I am following the pattern I found here:
http://blogs.msdn.com/b/henrikn/archive/2012/02/11/httpclient-is-here.aspx
Background:
Object I am deserializing is a POCO. Properties have no attributes. It is just a few value type properties and a couple collection properties. REST service appears to work ok also. When I look at the JSON returned by the service it appears to be OK.
Using Web API 2.1 5.1.2
Problem:
.. is calling HttpResponseMessage.Content.ReadAsAsync(). Sometimes it works (returns an object) and sometimes it doesn't (throws "Thread was being aborted" or returns null). It appears the content property can be read once only and subsequent reads throw errors. See comments in code below.
Related questions:
HttpContent.ReadAsAsync Deserialization issue
Question appears to be similar to mine. Answer indicates a bug but this is over two years old.
Code:
[TestMethod]
public void AddSiteTest()
{
// Use POST to create a resource i.e. insert. Use PUT to update.
Site site = new Site {SiteName = "Test", Active = true, URI="www.test.com" };
Site newSite = null;
client.PostAsJsonAsync<Site>(baseURI + "/Sites/AddSite?securityKey="+ SecurityKey, site).ContinueWith(x =>
{
HttpResponseMessage response = x.Result;
response.EnsureSuccessStatusCode();
if (response.IsSuccessStatusCode)
{
try
{
string str = Task.Run(() => response.Content.ReadAsStringAsync()).Result; // yep its json and it is a proprety serialized object
// Method 1 (preferred... ):
//Site siteA = Task.Run(() => response.Content.ReadAsAsync<Site>()).Result; // usuallly throws if content has been read
// Method 2:
Site siteB = response.Content.ReadAsAsync<Site>().Result; // usully returns a valid result (when I dont put a breakpoint on it). Does not deadlock.
// Method 3:
response.Content.ReadAsAsync<Site>().ContinueWith(d =>
{
Site siteC = d.Result; // returns null
});
}
catch (Exception ex)
{
string y = ex.Message;
}
}
});
}

try to use await:
string str = await response.Content.ReadAsStringAsync();
And you have to add async before void in your method.

Portable Class Library HttpClient

For one of my projects I want to develop a library that can be used in different platforms (Desktop, Mobile, Surface, etc). Hence have opted Porable Class Library.
I am developing a class for calling different API calls' using HttpClient. I am stuck with how to call the method, response and work around. This is my code :-
public static async Task<JObject> ExecuteGet(string uri)
{
using (HttpClient client = new HttpClient())
{
// TODO - Send HTTP requests
HttpRequestMessage reqMsg = new HttpRequestMessage(HttpMethod.Get, uri);
reqMsg.Headers.Add(apiIdTag, apiIdKey);
reqMsg.Headers.Add(apiSecretTag, ApiSecret);
reqMsg.Headers.Add("Content-Type", "text/json");
reqMsg.Headers.Add("Accept", "application/json");
//response = await client.SendAsync(reqMsg);
//return response;
//if (response.IsSuccessStatusCode)
//{
string content = await response.Content.ReadAsStringAsync();
return (JObject.Parse(content));
//}
}
}
// Perform AGENT LOGIN Process
public static bool agentStatus() {
bool loginSuccess = false;
try
{
API_Utility.ExecuteGet("http://api.mintchat.com/agent/autoonline").Wait();
// ACCESS Response, JObject ???
}
catch
{
}
finally
{
}
Like ExecuteGet, I will also create for ExecutePost. My query is from ExecuteGet, if (1) I pass JObject on parsing when IsSuccessStatusCode only, then how can I know about any other errors or messages to inform the user. (2) If I pass response, then how do I assign it here
response = API_Utility.ExecuteGet("http://api.mintchat.com/agent/autoonline").Wait();
that is giving error.
What would be the best approach to handle this situation ? And I got to call multiple API's, so different API will have different result sets.
Also, can you confirm that designing this way and adding PCL reference I will be able to access in multiple projects.
UPDATE :-
As mentioned in below 2 answers I have updated my code. As mentioned in the provided link I am calling the from the other project. This is my code :-
Portable Class Library :-
private static HttpRequestMessage getGetRequest(string url)
{
HttpRequestMessage reqMsg = new HttpRequestMessage(HttpMethod.Get, url);
reqMsg.Headers.Add(apiIdTag, apiIdKey);
reqMsg.Headers.Add(apiSecretTag, ApiSecret);
reqMsg.Headers.Add("Content-Type", "text/json");
reqMsg.Headers.Add("Accept", "application/json");
return reqMsg;
}
// Perform AGENT LOGIN Process
public static async Task<bool> agentStatus() {
bool loginSuccess = false;
HttpClient client = null;
HttpRequestMessage request = null;
try
{
client = new HttpClient();
request = getGetRequest("http://api.mintchat.com/agent/autoonline");
response = await client.SendAsync(request).ConfigureAwait(false);
if (response.IsSuccessStatusCode)
{
string content = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
JObject o = JObject.Parse(content);
bool stat = bool.Parse(o["status"].ToString());
///[MainAppDataObject sharedAppDataObject].authLogin.chatStatus = str;
o = null;
}
loginSuccess = true;
}
catch
{
}
finally
{
request = null;
client = null;
response = null;
}
return loginSuccess;
}
From the other WPF project, in a btn click event I am calling this as follows :-
private async void btnSignin_Click(object sender, RoutedEventArgs e)
{
/// Other code goes here
// ..........
agent = doLogin(emailid, encPswd);
if (agent != null)
{
//agent.OnlineStatus = getAgentStatus();
// Compile Error at this line
bool stat = await MintWinLib.Helpers.API_Utility.agentStatus();
...
I get these 4 errors :-
Error 1 Predefined type 'System.Runtime.CompilerServices.IAsyncStateMachine' is not defined or imported D:\...\MiveChat\CSC
Error 2 The type 'System.Threading.Tasks.Task`1<T0>' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Threading.Tasks, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b03f5f7f89d50a3a'. D:\...\Login Form.xaml.cs 97 21
Error 3 Cannot find all types required by the 'async' modifier. Are you targeting the wrong framework version, or missing a reference to an assembly? D:\...\Login Form.xaml.cs 97 33
Error 4 Cannot find all types required by the 'async' modifier. Are you targeting the wrong framework version, or missing a reference to an assembly? D:\...\Login Form.xaml.cs 47 28
I tried adding System.Threading.Tasks from the PCL library only, that gave 7 different errors. Where am I going wrong ? What to do to make this working ?
Please guide me on this. Have spend lots of hours figuring the best to develop a library accessible to desktop app & Win Phone app.
Any help is highly appreciative. Thanks.

If you call an async api when making the http calls, you should also expose that async endpoint to the user, and not block the request using Task.Wait.
Also, when creating a third party library, it is recommanded to use ConfigureAwait(false) to avoid deadlocks when the calling code tries to access the Result property or the Wait method. You should also follow guidelines and mark any async method with Async, so the method should be called ExecuteStatusAsync
public static Task<bool> AgentStatusAsync()
{
bool loginSuccess = false;
try
{
// awaiting the task will unwrap it and return the JObject
var jObject = await API_Utility.ExecuteGet("http://api.mintchat.com/agent/autoonline").ConfigureAwait(false);
}
catch
{
}
}
And inside ExecuteGet:
response = await client.SendAsync(reqMsg).ConfigureAwait(false);
string content = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
In case IsSuccessStatusCode is false, you may throw an exception to the calling code to show something went wrong. To do that, you can use the HttpResponseMessage.EnsureSuccessStatusCode which throws an exception if the status code != 200 OK.
Personally, if ExecuteGet is a public API method i would definitely not expose it as a JObject but a strongly typed type.

If you want the result of the task, you need to use the Result property:
var obj = API_Utility.ExecuteGet("http://api.mintchat.com/agent/autoonline").Result;
However, it's usually not a good idea to wait synchronously for an async method to complete, because it can cause deadlocks. The better approach is to await the method:
var obj = await API_Utility.ExecuteGet("http://api.mintchat.com/agent/autoonline");
Note that you need to make the calling method async as well:
public static async Task<bool> agentStatus()
Sync and async code don't play together very well, so async tends to propagate across the whole code base.

Accessing Result property of a Task

I am trying to retrieve the ID of an album using the C# Facebook SDK. However I am getting the below error:
System.Threading.Tasks.Task' does not contain a definition for 'Result' and no extension method 'Result' accepting a first argument of type 'System.Threading.Tasks.Task' could be found
Please see the below code, the error occurs on the foreach line
try
{
string wallAlbumID = string.Empty;
FacebookClient client = new FacebookClient(accessToken);
client.GetTaskAsync(pageID + "/albums")
.ContinueWith(task =>
{
if (!task.IsFaulted)
{
foreach (dynamic album in task.Result.data)
{
if (album["type"] == "wall")
{
wallAlbumID = album["id"].ToString();
}
}
}
else
{
throw new DataRetrievalException("Failed to retrieve wall album ID.", task.Exception.InnerException);
}
});
return wallAlbumID;
}
For the record, the FacebookClient.GetTaskAsync method returns Task<object>

I don't know the Facebook API, but the error seems to indicate, that you're dealing with Task class (non-generic) which does not have Result property. It is the generic Task<T> derived from non-generic Task class that has the property. They both allow to run code asynchronously, but the generic class is able to run methods that return values.
If GetTaskAsync returns Task and not Task<T>, then it means you can't get the result from it, as the operation it runs in the background does not return anything.

When I compile your code, I get two errors, the first one is the one you mentioned, and the second one is:
'object' does not contain a definition for 'data' and no extension method 'data' accepting a first argument of type 'object' could be found
This second error is your actual error: task.Result is an object, but (I assume) you want to treat it as dynamic. Because of this error, the compiler also tries to use the overload of ContinueWith() that uses just Task, not Task<object>, which is why you're also getting the first error.
To fix this error, you should cast task.Result to dynamic:
dynamic result = task.Result;
foreach (dynamic album in result.data)
This will compile fine, but it won't actually work, because you set the local variable after you return from the enclosing method.
If you're using C# 5.0, you should use await here, instead of ContinueWith():
try
{
dynamic result = await client.GetTaskAsync(pageID + "/albums");
foreach (dynamic album in result.data)
{
if (album["type"] == "wall")
{
return (string)album["id"].ToString();
}
}
return string.Empty;
}
catch (Exception e) // you should use a specific exception here, but I'm not sure which
{
throw new DataRetrievalException("Failed to retrieve wall album ID.", e);
}
If you can't use C# 5.0, then your whole method should return a Task<string> that's returned by ContinueWith():
return client.GetTaskAsync(pageID + "/albums")
.ContinueWith(
task =>
{
if (!task.IsFaulted)
{
dynamic result = task.Result;
foreach (dynamic album in result.data)
{
if (album["type"] == "wall")
{
return (string)album["id"].ToString();
}
}
return string.Empty;
}
else
{
throw new DataRetrievalException(
"Failed to retrieve wall album ID.", task.Exception.InnerException);
}
});