I am able to write a "Task" function to get the text from a single web page. But I want to make a function that takes the url as an input and returns the text from the web page (so that I can keep the GET part separate from the rest of my code.
Here is the code that I have working:
Private components As System.ComponentModel.IContainer
ReadOnly client As HttpClient = New HttpClient()
Private Async Function MyWebResponse() As Task
Dim myUrl As String
myUrl = "https://statsapi.mlb.com/api/v1.1/game/632201/feed/live/diffPatch"
' Call asynchronous network methods in a try/catch block to handle exceptions.
Try
Dim response As HttpResponseMessage = Await client.GetAsync(myUrl)
response.EnsureSuccessStatusCode()
Dim responseBody As String = Await response.Content.ReadAsStringAsync()
Catch e As HttpRequestException
Console.WriteLine(Environment.NewLine & "Exception Caught!")
Console.WriteLine("Message :{0} ", e.Message)
MsgBox(e.Message)
End Try
End Function
I want to turn this into a function that returns the responseBody as a string. Something like:
Dim myUrl As String
myUrl = "https://statsapi.mlb.com/api/v1.1/game/632201/feed/live/diffPatch"
myString = MyWebResponse(myUrl)
I haven't been able to figure out a way to convert the function to the kind that returns something. If I make it into Task(Of String) it fails because you can't put a Task(Of String) into a String variable. But if I try to make it a string instead of a Task then I can't have the async and Await stuff and then the Httpclient commands don't work because they require async and Await. At this point it looks like all of my code has to go into a single block of code where I loop through urls and do stuff with the responses. But if I can't make the code modular, it will be extremely difficult to work with and maintain.
Related
Hello I am trying to access a webform with data. However my code does not have error but its not working. It is supposed to send me a text message using the Web API provided by the telco carrier. Any assistance and advise will be greatly appreciated.
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Try
Dim client As New HttpClient
Dim url = $"some url"
Dim data2 = "{""username"": ""someuname"", ""password"":""somepass"", ""msisdn:""some number"", ""content:""Hello, this is a sample broadcast"", ""shortcode_mask:""somemask""}"
Dim payload = Newtonsoft.Json.JsonConvert.SerializeObject(data2)
Dim buffer = Encoding.UTF8.GetBytes(payload)
Dim bytes = New Net.Http.ByteArrayContent(buffer)
bytes.Headers.ContentType = New Net.Http.Headers.MediaTypeHeaderValue("application/json")
Dim request = client.PostAsync(url, bytes)
Catch Ex As Exception
Console.WriteLine()
End Try
End Sub
End Class
There are a few issues in your code. Let me start with the most important one first:
Catch Ex As Exception
Console.WriteLine()
End Try
This code means: If an error occurs, throw away all useful information about the error that could help me find the cause, then write an empty line to the console and pretend nothing bad happened.
Don't do that. Remove the whole try-catch block, then re-run your code again. If you get an exception: That's great, because .NET is now telling you what is wrong with your code! If you understand the error message, use it to fix your code. If you don't understand it, feel free to ask the community on StackOverflow.
Second issue:
This line
Dim request = client.PostAsync(url, bytes)
starts an asynchronous web request. You don't wait for the result, so you don't know whether it succeeded or not.
You're supposed to Await async methods, but if you aren't familiar with the async/await pattern yet, I won't be able to give you all the necessary background in the single StackOverflow answer. Until you have familiarized youself with async/await, you can synchronously wait for the result by accessing the Result property of the Task that has been returned:
Dim response = client.PostAsync(url, bytes).Result
response.EnsureSuccessStatusCode()
Third issue: You JSON-serialize something which is already JSON. If your data is already JSON, just use it as the payload without calling SerializeObject.
Your data2 is a string. When you use the JSON library to serialize it, it probably isn't in the JSON structure that your URL endpoint expects. Create a Type, fill it with data, and pass that to your JsonCoverter
Thank you Heinzi, here is the final working code based on your concepts:
Public Class Form1
Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim client As New HttpClient
Dim url = $"some url"
Dim data2 = "
{""username"": ""some uname"", ""password"": ""somepass"", ""msisdn"": ""somenumber"", ""content"": ""Hello, this is a sample broadcast"", ""shortcode_mask"" :""somemask""}"
Dim buffer = Encoding.UTF8.GetBytes(data2)
Dim bytes = New ByteArrayContent(buffer)
bytes.Headers.ContentType = New Headers.MediaTypeHeaderValue("application/json")
Dim request1 = Await client.PostAsync(url, bytes)
Dim response = client.PostAsync(url, bytes).Result
response.EnsureSuccessStatusCode()
End Sub
End Class
I can now receive text messages :)
Need help in solving error in HTTP GET request [closed]
I have the following code in VB.NET framework which should pull the data in json format and add it to a list view control using GET request. However I am getting following error:
System.Threading.Tasks.Task.FromResult(System.Net.Http.HttpResponseMessage)
Dim client = New HttpClient()
client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", "{Subscription-Key}")
Dim uri = "https://example.com/" & SearchKey
Dim response = client.GetAsync(uri)
lstMer.Items.Add(response.ToString)
Initially I wrote the following code in VBA and it was working fine:
Dim jsonText as String
Set req = New MSXML2.ServerXMLHTTP60
key_id = "{Subscription-Key}"
key_header_name = "Subscription-Key-Id"
liveURL = "https://example.com/" & SearchKey
req.Open "GET", liveURL, False
req.setRequestHeader {Subscription-Key-Id}, {Subscription-Key}
req.setRequestHeader "Host", "site Address"
req.send
jsonText = req.responseText
The requirement is to get the headers from URL and fill a list view.
I think I understand. You don't get an error
System.Threading.Tasks.Task.FromResult(System.Net.Http.HttpResponseMessage)
rather you get that as a result of response.ToString(). This is because you are calling client.GetAsync(uri) directly, which returns a Task.FromResult<TResult>. However, it is meant to be run async, and there are some convenient keywords for achieving this, namely Async / Await. If you await the task, instead of returning a Task.FromResult<TResult>, it will return a TResult. So change your code to do just that
Private Async Sub Foo()
Dim client = New HttpClient()
client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", "{Subscription-Key}")
Dim uri = "https://example.com/" & SearchKey
Dim response = Await client.GetAsync(uri)
lstMer.Items.Add(response.ToString)
End Sub
See HttpClient.GetAsync and about what it returns Task.FromResult
I have a webservice GetCard which calls a function CreateRaces. Inside the CreateRaces I am saving the new objects. This works fine without async. However, when I call the async function for task1 CommitAsync the method executes and returns a response without hitting the next break point. I have tried to work around with via Task.Run, ConfigureWait(true), and with
With HttpContext.Current
bulk.Setup etc...
End With
but nothing seems to work.
The bulk.Setup - CommitAsync calls a third party dll (SqlBulkTools) which returns Task.
It looks like it works on a different thread.
Any ideas how to configure it so I the function executes and I can hit the next break point which is sw.Stop()?
<HttpGet>
<AllowAnonymous>
Public Async Function GetCard(cardurl As String) As HttpResponseMessage
Try
Dim oRace As New RaceCard(cardurl)
oRace.DoWork()
Dim oRC As New RaceController
await oRC.CreateRaces(oRace.Races)
Return Request.CreateResponse(HttpStatusCode.OK, True.ToJson)
Catch ex As Exception
Return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, ex)
End Try
End Function
CreateRaces function
Public Async Function CreateRaces(ByVal t As List(Of Race)) As Threading.Tasks.Task(Of Boolean)
Try
'Proceed only if list has items
If t.Count > 0 Then
Dim bulk As New BulkOperations()
Dim sw As New Stopwatch()
Dim oCon As New SqlClient.SqlConnection(DotNetNuke.Common.Utilities.Config.GetConnectionString)
sw.Start()
Dim task1 = Await bulk.Setup(Of Race).ForCollection(t).WithTable("ArbiRace").AddAllColumns().BulkInsertOrUpdate().SetIdentityColumn(Function(i) i.RaceID).MatchTargetOn(Function(m) m.RaceName).CommitAsync(oCon).ConfigureAwait(True)
sw.Stop()
Dim swt = sw.ElapsedMilliseconds
End If
Return True
Catch ex As Exception
Dim s As String
s = ex.ToString
Return False
End Try
End Function
Asnyc calls can be handled in 2 ways:
Deliberately halting thread execution until one, several, or all tasks are completed.
Leaving the task to run while the current thread goes to do something else.
Based on your question, you are expecting #1, but your code currently does #2. Await Documentation:
An Await expression or statement does not block the thread on which it is executing. Instead, it causes the compiler to sign up the rest of the async method, after the Await expression, as a continuation on the awaited task. Control then returns to the caller of the async method. When the task completes, it invokes its continuation, and execution of the async method resumes where it left off.
In your case, once CreateRaces() reaches the Dim task1 line (which will eventually store the result, not the task), control returns to GetCard(). However, the CreateRaces() call here also uses an Await, so control attempts to go back up the call stack again. Except, there is nowhere left to go up, because you are at the original endpoint. This is why you seem to get a response too soon.
Since you are waiting for the task to finish to get the elapsed time, you want to wait for the tasks to finish before returning a response. This can be accomplished with task.Result, task.Wait(), or the shared method Task.WaitAll().
Example:
<HttpGet>
<AllowAnonymous>
Public Function GetCard(ByVal cardUrl As String) As HttpResponseMessage
Try
Dim oRace As New RaceCard(cardurl)
oRace.DoWork()
Dim oRC As New RaceController
Dim createRacesTask As Threading.Tasks.Task(Of Boolean) = oRC.CreateRaces(oRace.Races)
'Do other tasks here while we wait
Threading.Tasks.Task.WaitAll(createRacesTask, ...)
Return Request.CreateResponse(HttpStatusCode.OK, True.ToJson)
Catch ex As Exception
Return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, ex)
End Try
End Function
I have nearly completed a basic OneDrive interface, and am able to handle creating and writing folders, files, and so forth. The last element to get working is to update a file's date/time stamp to match that of the local (originating) file.
When I drop a file via the browser interface, the file's date/time stamp shows correctly in the view. This is reflected in the "client_updated_time" when I read the file's properties later in my application. Clear enough.
However, I cannot find any way to update this field programmatically from within my application. I am using the following code, to no avail. I have a valid _accessToken value, a valid fileId for the new file, and the call results always indicates success.
The "name" and "updated_time" elements are just in there to see if anything happens, and the file will indeed rename if I mangle the fileName variable a bit. I didn't expect the "updated_time" to updated, but it seems to me that the "client_updated_time" element should work.
Using fiddler, it appears that the browser-based interface (java?) opens a session, sends the file over, and then in the close-session call uses a header entry labelled "X-Last-Modified-ISO8601" to set the file's date-time stamp. However, using the REST interface, I cannot find any examples of this. The documentation for setting file properties mentions renaming only (which works in this code).
Any feedback on how to accomplish setting "client_updated_time" with REST calls would be much appreciated!
Here's the relevant code:
Private _liveURL As String = "https://apis.live.net/v5.0/"
Private Sub AddAuthorizationHeader(hc As HttpClient, authorization As String)
If Len(authorization) > 0 Then
hc.DefaultRequestHeaders.Authorization = New Headers.AuthenticationHeaderValue("Bearer", authorization)
End If
End Sub
Public Function WebPUT(uri As String, contentType As String, authorization As String, data As String) As String
Dim response As String = String.Empty
Try
Dim hc As New HttpClient()
Dim content As New Http.StringContent(data, System.Text.Encoding.UTF8, contentType)
AddAuthorizationHeader(hc, authorization)
Using r = hc.PutAsync(uri, content).Result
response = r.Content.ReadAsStringAsync.Result
End Using
Catch ex As Exception
' fake it
response = "{""error"": {""code"": ""invalid_request"", ""message"": """ + ex.Message + """}}"
End Try
Return response
End Function
Private Function UpdateFileDateTime(fileId As String, fileName As String, fileDt As String) As Boolean
Dim response As Boolean = False
Dim wr As String = WebHelper.WebPUT(_liveURL + fileId, "application/json", _accessToken, "{ ""name"": """ + fileName + """, ""updated_time"": """ + fileDt + """, ""client_updated_time"": """ + fileDt + """ }")
'... parse wr for response
Return response
End Function
Based on the file object reference, that field is read-only via the REST API: http://msdn.microsoft.com/en-us/library/dn631834.aspx
I've got a vs2010, 4.0 vb.net, WinForms app calling AttemptLogin on a form load event.
I want to avoid blocking the form load if possible and I was hoping the tasks and continuation stuff in 4.0 would be the right way to go as I could run the main task on the default scheduler and the continuation on fromcurrentsynchronisationcontext but although I've got the OnAttemptLogin working I can't get my OnAttemptLoginCompleted function in the continuation to be called.
I think it's because the OnAttemptLogin returns a "RunToCompletion" task so the continuation never gets called. But I don't know how to deal with that, I've tried numerous things but I've now confused myself so much I'm pretty much mashing keys. Can anyone offer any advice? Am I simply doing it wrong or have I got the wrong idea all together?
Here's what I have so far, the OnAttemptLogin works as I would expect it to, but it then never calls the LongRunning tasks continuation.
Please note: I can't use await as I'm in vs2010 .net4.0 so I'm stuck with ContinueWith.
Public Sub AttemptLogin(OnAttemptLoginCompleted As Action(Of Task(Of HttpResponseMessage)))
Try
Dim LongRunningTask As Task(Of HttpResponseMessage) = Task.Factory.StartNew(Function()
Return OnAttemptLogin()
End Function, TaskScheduler.Default)
Dim UITask As Task(Of HttpResponseMessage) = LongRunningTask.ContinueWith(Sub(t)
OnAttemptLoginCompleted(t)
End Sub, TaskScheduler.FromCurrentSynchronizationContext)
LongRunningTask.Wait()
Catch ex As AggregateException
' nom nom nom
' do something useful
End Try
End Sub
Private Function OnAttemptLogin() As Task(Of HttpResponseMessage)
Dim aClient = New HttpClient()
Using (aClient)
' CREATE REQUEST
aClient.DefaultRequestHeaders.Accept.Add(New MediaTypeWithQualityHeaderValue("application/json"))
aClient.DefaultRequestHeaders.Add("Authorization", "Basic " + Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes(String.Format("{0}:{1}", CallingDTO.Email, CallingDTO.Password))))
UserQueryDTO.UserName = UserDTO.Email
UserQueryDTO.Password = UserDTO.Password
Dim url As String = DnnRequest.GetUrl(Credentials.HttpAlias, cstModuleAssembly, "User", "CanLogin", False)
' POST REQUEST
Dim p As Task(Of HttpResponseMessage) = aClient.PostAsJsonAsync(url, UserQueryDTO).ContinueWith(Function(x)
' READ RESPONSE
Dim r = x.Result.Content.ReadAsAsync(Of HttpResponseMessage)()
r.Wait()
Return r.Result
End Function)
Try
p.Wait()
Catch ex As Exception
End Try
Return p
End Using
End Function
The problem here is ... convoluted. The main issue you have here, the reason why UITask won't run, is because LongRunningTask is not of type Task(Of HttpResponseMessage). It is actually a Task(Of Task(Of HttpResponseMessage)). OnAttempLogin() returns a Task(of H...), but the task that you start in form load is a Task that will return that Task, hence, Task(Of Task(Of ...)). So there's an exception in that line, hence the UITask line never runs. So the problem with the code is that there's too many Task things all over the place.
The other problem is that you aren't really doing anything asynchronously (except that part that never ran) since you are Wait()-ing for all the tasks. So you need to get rid of most of your waits to actually achieve that. Getting rid of the waits means you need to handle exceptions with a continuation.
Some minor points:
You don't really need the scheduler stuff, either.
UITask is simply a Task, not a Task(Of ...) since it doesn't return anything.
I'm continuing from UITask to handle exceptions so that it also catches UITask's exceptions. If I continued from LongRunningTask, I would miss those exceptions.
Below is an example of what I think the new code will look like. There may be a few syntax issues since I'm missing a few things to get this to compile:
Public Sub AttemptLogin(OnAttemptLoginCompleted As Action(Of Task(Of HttpResponseMessage)))
Dim LongRunningTask As Task(Of HttpResponseMessage) = OnAttemptLogin()
Dim UITask As Task = LongRunningTask.ContinueWith(AddressOf OnAttemptLoginCompleted)
uiTask.ContinueWith(Sub(t)
Dim ex As AggregateException = t.Exception
'nom nom nom
'all your exceptions will end up here.
End Sub, TaskContinuationOptions.OnlyOnFaulted)
End Sub
Private Function OnAttemptLogin() As Task(Of HttpResponseMessage)
Dim aClient = New HttpClient()
Using (aClient)
' CREATE REQUEST
aClient.DefaultRequestHeaders.Accept.Add(New MediaTypeWithQualityHeaderValue("application/json"))
aClient.DefaultRequestHeaders.Add("Authorization", "Basic " + Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes(String.Format("{0}:{1}", CallingDTO.Email, CallingDTO.Password))))
UserQueryDTO.UserName = UserDTO.Email
UserQueryDTO.Password = UserDTO.Password
Dim url As String = DnnRequest.GetUrl(Credentials.HttpAlias, cstModuleAssembly, "User", "CanLogin", False)
' POST REQUEST
Dim p As Task(Of HttpResponseMessage) = aClient.PostAsJsonAsync(url, UserQueryDTO).ContinueWith(Function(x)
' READ RESPONSE
Dim r = x.Result.Content.ReadAsAsync(Of HttpResponseMessage)()
r.Wait()
Return r.Result
End Function)
Try
p.Wait()
Catch ex As Exception
End Try
Return p
End Using
End Function
my solution was to delete everything and give up, i will use something else, anything else, pff at this point ill lock the ui and not care, three days on this rubbish is crazy.
Marking jtseng's reply as correct even though it didnt work as hes the only reply and deserves something for taking the time to try and help.