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Error reading file async

I had a problem to download a file ( an Image ) and someone recommended to me to do asynchronously.

I changed my code so :

Async Function _take_file(ByVal _file As String) As Task

....

Dim client As HttpClient = New HttpClient()

Dim _Request As HttpRequestMessage = New HttpRequestMessage(HttpMethod.Post, "https://content.dropboxapi.com/2/files/download")
_Request.Headers.Add("Authorization", "Bearer " + _token)
_Request.Headers.Add("Dropbox-API-Arg", _parametro)

Dim _response As HttpResponseMessage = Await client.SendAsync(_Request)

Dim _responseStream As Stream = Await _response.Content.ReadAsStreamAsync()
Dim myStreamReader As New StreamReader(_responseStream)

I have an error on the last line :

System.NullReferenceException was unhandled
Message: An unhandled exception of type 'System.NullReferenceException' occurred in mscorlib.dll

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Comments

Здравко

@Lukag wrote:
...
Dim myStreamReader As New StreamReader(_responseStream)
...

Hm..🤔 Let's see what's going on here. Does the 'myStreamReader' variable get declared here, or get value assigned, or...? 🧐

Lukag

Hm both ?

i thought that it declared and that got value.

Здравко

@Lukag wrote:
...
Dim client As HttpClient = New HttpClient()
...
Dim myStreamReader As New StreamReader(_responseStream)
...

Then, what's different and common in above code lines (aside of different types)?

Lukag

In first case a define the object and i create as a new httpclient

in the second i declare ad object as a new streamreader using data from response .

In the code of example i see i thought it works so 🙂

Здравко

Your error message means that in your code you have used something not initialized at that time. That's it.

Lukag

Yes but i don't understand.

First of all, in you opinion is correct use streamreader ?

I don't want become crazy and after i have other problems 🙂

Здравко

@Lukag wrote:
...
First of all, in you opinion is correct use streamreader ?
...

What you use is matter of design decision, so don't ask anybody else. The best way follows what you're doing. If you don't know what are you doing... no way to decide what's the best (or even to suppose).

Such questions are not Dropbox API related though. If you have something to learn about programing lang in use, read some tutorial or similar.

Lukag

i'm learning and reading guides and tutorial but the error made me worry that API were missing something and so I asked for your help

Здравко

🙂 Ok. Where is the API related error, mistake, mismatching, etc? What are you getting as error response? What is the status code? All are questions, you have to answer, and one of them at least have to be related to Dropbox API (the same for any other API)!

Greg-DB

I see you're getting a System.NullReferenceException. As Здравко said, that's not an error from the Dropbox API itself. You can find Microsoft's documentation for that exception here though.

Lukag

ok i understand but the error is in : Dim myStreamReader As New StreamReader(_responseStream)

and i thought that was connected to the call https://content.dropboxapi.com/2/files/download