I am trying to use a Web Service to return Json for a Collection of Users from a Database Table. I'm only new to .NET (< 1 week experience), and I don't want to use the UpdatePanel for AJAX. I have tried using the JavaScriptSerializer as well as Json.NET to serialize. Both cases seem to spawn an Infinite Loop.
What am I doing wrong? Is there a better way to do this? I appreciate any suggestions. Thanks.
Dim myUser As New HagarDB.Users
myUser.Read()
'Dim jsSerializer As New System.Web.Script.Serialization.JavaScriptSerializer
'Dim sbUsers As New System.Text.StringBuilder
'jsSerializer.Serialize(myUser, sbUsers)
Dim json = JsonConvert.SerializeObject(myUser, Formatting.Indented)
Thanks to RPM1984 for suggesting DataContractJsonSerializer. Here is the working code:
Public Function GetUsers() As String
Dim myUser As New HagarDB.Users
Dim jsonSerializer As New DataContractJsonSerializer(GetType(HagarDB.Users))
Dim stream As New MemoryStream()
myUser.Read()
jsonSerializer.WriteObject(stream, myUser)
Dim json As String = Encoding.[Default].GetString(stream.ToArray())
stream.Close()
Return json
End Function
Related
Receiving below error on deserializing json to dataset.
Unexpected JSON token when reading DataTable. Expected StartArray, got Integer. Path 'id', line 1, position 9
Json Retrieved : {"id":130,"type":"general","setup":"test?","punchline":"test."}
My Code
Dim wc As New WebClient
Try
Dim res As String
For i = 0 To 5
res = wc.DownloadString("https://official-joke-api.appspot.com/random_joke")
Dim jObject = JsonConvert.DeserializeObject(res)
Dim ds As New DataSet
ds = JsonConvert.DeserializeObject(Of DataSet)(res)
MsgBox(ds.Tables.Count)
Next
Catch ex As Exception
MsgBox(ex)
End Try
As user Akshay Gaonkar commented, you can give Newtonsoft.Json a class, named, say, Joke, to deserialise with. You can get around the mismatch of uppercase/lowercase initial letter naming conventions by decorating the properties with <JsonProperty("nameInTheJson")>.
Instead of deserializing the data into a datatable inside a dataset, you could keep it simple and create a List(Of Joke).
This is for a console application:
Imports System.Net
Imports Newtonsoft.Json
Module Program
Class Joke
<JsonProperty("id")>
Property Id As Integer
<JsonProperty("type")>
Property Type As String
<JsonProperty("setup")>
Property Setup As String
<JsonProperty("punchline")>
Property Punchline As String
End Class
Sub Main(args As String())
Dim jokes As New List(Of Joke)
Using wc As New WebClient()
For i = 1 To 5
Dim jokeInfo = wc.DownloadString("https://official-joke-api.appspot.com/random_joke")
jokes.Add(JsonConvert.DeserializeObject(Of Joke)(jokeInfo))
Next
End Using
' Alternative which fetches ten jokes in one go - note the use of (Of List(Of Joke))
'Using wc As New WebClient()
' Dim jokeInfo = wc.DownloadString("https://official-joke-api.appspot.com/jokes/ten")
' jokes = JsonConvert.DeserializeObject(Of List(Of Joke))(jokeInfo)
'End Using
For Each jk In jokes
Console.WriteLine($"{jk.Setup}{vbCrLf}{jk.Punchline}{vbCrLf}")
Next
End Sub
End Module
The Using statement is needed because a WebClient should be disposed of after use to clear up system resources. (You could use the equivalent Try...Finally with wc.Dispose() instead.)
The JSON you showed is invalid. Datatable is expecting array of Object , so the JSON should look like below :
[{"id":130,"type":"general","setup":"test?","punchline":"test."}]
I am able to write to the file perfectly... however I am having trouble reading from file and inserting read data into a listbox.
Public myData As New MySettings
Public saveFile As String = ("mysettings.ini")
'SAVE INFO TO SETTINGS FILE
Dim fs As Stream = New FileStream(saveFile, FileMode.Create)
Dim bf As BinaryFormatter = New BinaryFormatter()
For l_index As Integer = 0 To ListBox1.Items.Count - 1
Dim l_text As String = CStr(ListBox1.Items(l_index))
bf.Serialize(fs, l_text)
Next
fs.Close()
Return
This is the part where I am having trouble...
'LOAD INFO FROM SETTINGS FILE
Dim fs As Stream = New FileStream(saveFile, FileMode.Open)
Dim bf As BinaryFormatter = New BinaryFormatter()
For l_index As Integer = 0 To saveFile.Count - 1
Dim l_text As String = CStr(saveFile(l_index))
'myData = CType(bf.Deserialize(fs), CType(myData))
ListBox1.Items.Add(myData)
Next
fs.Close()
Return
Any help at all would be appreciated, even a point in the right direction.
Thanks in advance!!
The ListBox ObjectCollection (Items) is not marked as serializable, so you cant serialize the entire thing at once. You may have encountered this and used the loop to serialize each item. The loop does appear to serialize each item, but I don't know how you can deserialize in a loop - you wont know how many items there are, nor will the Serializer.
Rather than one item at a time, you could copy the ListBox items to an array and serialize the entire thing:
Dim ary(lb.Items.Count - 1) As Object
lb.Items.CopyTo(ary, 0)
' OpenOrCreate!
Using fs As New FileStream("C:\Temp\lbitems.bin", FileMode.OpenOrCreate)
Dim bf As New BinaryFormatter
bf.Serialize(fs, ary)
End Using ' close and dispose of stream
Deserialization is just the reverse:
Using fs As New FileStream("C:\Temp\lbitems.bin", FileMode.Open)
Dim bf As New BinaryFormatter
Dim myAry = bf.Deserialize(fs)
lb.Items.Clear()
lb.Items.Add(myAry)
End Using
You can make it a bit simpler using a List(of String) and assign it as the DataSource.
Private myLBItems As New List(Of String)
...
' fake items to add
myLBItems.Add("Foo")
myLBItems.Add("Bar")
myLBItems.Add("Option")
myLBItems.Add("Strict")
lb.DataSource = myLBItems
Using the List as the DataSource, you dont have to copy items from here to there - whatever is in the List will appear in the ListBox. Serialization is simple too:
bf.Serialize(fs, myLBItems)
Since Deserializing returns an Object, you need to cast it (Option Strict):
myLBItems = CType(bf.Deserialize(fs), List(Of String))
Note: This may not be doing what you want at all. Your code is serializing what is in the ListBox after converting it to String. Later, it looks like you want to Deserialize to a MySettings Type.
If MySettings is something like a Name and Value pair (or collection of them), probably half the data and all the Type information will have been lost.
I thought this would be an easy task but I seem to have gotten lost in a rabbit hole.
I am trying to convert a class to XML and then a byte array in order to send it as the content of a HTTPWebRequest for a WCF Restful webservice. My code will return the class as XML in the Byte Array but the format is incorrect. The XML looks like this:
<?xml version="1.0" encoding="utf-8"?><Person xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><FirstName>Richard</FirstName><LastName>Cranium</LastName></Person>
I was attempting to use the OmitXmlDeclaration method thinking this would eliminate the extra declarations but it does not work with the xmltextwriter object and when I use the xmlwriterobject I can't determine how convert the outcome to a Byte array.
Here is my code:
Private Shared Function GenerateXMLPersonAsByte(strFirstName As String, strLastName As String) As Byte()
' This should serialize this to a byte array
Dim p As New Person()
p.FirstName = strFirstName
p.LastName = strLastName
' Want to use this with the xmlTextWriter but it does not support the property it is to be used with the XMLWriter instead
'Dim settings As XmlWriterSettings = New XmlWriterSettings()
'settings.OmitXmlDeclaration = True
'settings.ConformanceLevel = ConformanceLevel.Fragment
'settings.CloseOutput = False
' Create the XmlWriter object and write some content.
Dim mStream As New MemoryStream()
Dim ser As New XmlSerializer(GetType(Person))
Dim xmlTW As New XmlTextWriter(mStream, Encoding.UTF8)
ser.Serialize(xmlTW, p)
mStream = DirectCast(xmlTW.BaseStream, MemoryStream)
mStream.Close()
Return mStream.ToArray()
End Function
What must I do in order to get the XML with the correct opening tag?
or
How do I get the output from the XmlTextWriter object to a byte array?
I can't answer the whole question, but convert to string first
Dim myXmlString As String
Dim myStringWriter As New StringWriter()
Dim myXmlTextWriter As XmlTextWriter = New XmlTextWriter(myStringWriter)
'Write XML, and then flush the writer...
myXmlTextWriter.Flush()
'Return text from string writer...
myXmlString = myStringWriter.ToString()
'Close the Objects...
myStringWriter.Close()
myXmlTextWriter.Close()
then convert to byte using (sorry, C#, but you get the .NET call)
byte[] data = ASCIIEncoding.UTF8.GetBytes(myXmlString);
Reading binary data out of the database, and I need to convert it back into a Digital Persona fingerprint template. I'm not familiar with serialization and deserialization, so I could use a bit of help. Here's what I tried:
Dim rsBioData As SqlDataReader = SQL.ExecuteReader
Dim byteTemplate As Byte
Dim memStreamTemplate As MemoryStream
If rsBioData.HasRows Then
While rsBioData.Read
byteTemplate = rsBioData("BiometricData")
memStreamTemplate = New MemoryStream(byteTemplate)
Me.Template = DirectCast(template.DeSerialize(memStreamTemplate), DPFP.Template)
End While
End If
rsBioData.Close()
I receive an error that template.DeSerialize(memStreamTemplate) does not create a value.
For kicks, here's how I serialized the object to place it into the database. I assume this part is working, since the binary data shows up in SQL server--just can't read it back out to see.
Dim str As New MemoryStream
Enroller.Template.Serialize(str)
Dim serializedTemplate As Byte() = str.ToArray()
SQL.Parameters.AddWithValue("biometricData", serializedTemplate)
Thanks
Here's how I was finally able to do it. I was SO close the first time around.
byteTemplate = rsBioData("BiometricData")
memStreamTemplate = New MemoryStream(byteTemplate)
Me.Template.DeSerialize(memStreamTemplate)
I am generating this XML using the serializer in VB.net as shown below
Dim string_writer As New StringWriter()
Dim serializer As New XmlSerializer(GetType(MyClass))
serializer.Serialize(string_writer, addr)
txttest.Text = string_writer.ToString()
though it is returning XML, I see xmlns="http://tempuri.org/ in all the elements, is there anyway I hide this one.
Sure - just pass the default namespace you want to use to the constructor of your XmlSerializer:
Dim string_writer As New StringWriter()
Dim serializer As New XmlSerializer(GetType(MyClass), "")
serializer.Serialize(string_writer, addr)
txttest.Text = string_writer.ToString()
That should do the trick.