How do you get the key value from a vb.net collection when iterating through it?
Dim sta As New Collection
sta.Add("New York", "NY")
sta.Add("Michigan", "MI")
sta.Add("New Jersey", "NJ")
sta.Add("Massachusetts", "MA")
For i As Integer = 1 To sta.Count
Debug.Print(sta(i)) 'Get value
Debug.Print(sta(i).key) 'Get key ?
Next
Pretty sure you can't from a straight Microsoft.VisualBasic.Collection.
For your example code above, consider using a System.Collections.Specialized.StringDictionary. If you do, be aware that the Add method has the parameters reversed from the VB collection - key first, then value.
Dim sta As New System.Collections.Specialized.StringDictionary
sta.Add("NY", "New York")
'...
For Each itemKey in sta.Keys
Debug.Print(sta.Item(itemKey)) 'value
Debug.Print(itemKey) 'key
Next
I don't recommend using the Collection class, as that is in the VB compatibility library to make migrating VB6 programs easier. Replace it with one of the many classes in the System.Collections or System.Collections.Generic namespace.
It is possible to get a key with using Reflection.
Private Function GetKey(Col As Collection, Index As Integer)
Dim flg As BindingFlags = BindingFlags.Instance Or BindingFlags.NonPublic
Dim InternalList As Object = Col.GetType.GetMethod("InternalItemsList", flg).Invoke(Col, Nothing)
Dim Item As Object = InternalList.GetType.GetProperty("Item", flg).GetValue(InternalList, {Index - 1})
Dim Key As String = Item.GetType.GetField("m_Key", flg).GetValue(Item)
Return Key
End Function
Not using VB.Collection is recommended but sometimes we are dealing with code when it was used in past. Be aware that using undocumented private methods is not safe but where is no other solution it is justifiable.
More deailed information can be found in SO: How to use reflection to get keys from Microsoft.VisualBasic.Collection
Yes, it may well, but I want recomend that you use another Collection.
How to do you do with Reflection, the type Microsoft.VisualBasic.Collection contains some private fields, the field one should use in this case is "m_KeyedNodesHash" the field, and the field type is System.Collections.Generic.Dictionary(Of String, Microsoft.VisualBasic.Collection.Node), and it contains a property called "Keys", where the return type is System.Collections.Generic.Dictionary(Of String, Microsoft.VisualBasic.Collection.Node).KeyCollection, and the only way to get a certain key is to convert it to type IEnumerable(Of String), and the call ElementAt the function.
Private Function GetKey(ByVal col As Collection, ByVal index As Integer)
Dim listfield As FieldInfo = GetType(Collection).GetField("m_KeyedNodesHash", BindingFlags.NonPublic Or BindingFlags.Instance)
Dim list As Object = listfield.GetValue(col)
Dim keylist As IEnumerable(Of String) = list.Keys
Dim key As String = keylist.ElementAt(index)
Return key
End Function
Related
I want to make a collection to have data available
Example:
Dim b As New Collection
colb = New Collection
b.Add("system", "1001", "SYSTEM")
b.Add("network", "1002", "NETWORKA")
b.Add("networksecond", "1010", "NETWORKB")
colb.Add(b, "list")
im looking for a function to get data from this collection:
I want to, based on the ID (Second number) get the first and third value
So if I search for 1010, I need to have the value Network and NETWORKA
VB6 called, they want their Collection back.
No, seriously, please consider using a Dictionary instead of the old, legacy Collection class. Behold the beauty of generics and strong typing:
Dim dic As New Dictionary(Of Integer, Tuple(Of String, String))
dic.Add(1001, Tuple.Create("system", "SYSTEM"))
dic.Add(1002, Tuple.Create("network", "NETWORKA"))
dic.Add(1010, Tuple.Create("networksecond", "NETWORKB"))
' Search
Dim t As Tuple(Of String, String) = Nothing
If dic.TryGetValue(1002, t) Then
Console.WriteLine(t.Item1) ' prints "network"
Console.WriteLine(t.Item2) ' prints "NETWORKA"
End If
As soon as you have more than two values, I suggest that you use a specialized class instead of a Tuple to increase readability.
Also, you can simply use List(Of T). In most cases this is enough. Dictionary is good for fast search out long list by a single key.
'declare model
Public Class NetworkModel
Public Property Id As Integer
Public Property Name1 As String
Public Property Name2 As String
End Class
' load list of models
Private _modelList As New List(Of NetworkModel)()
.......
' search using LINQ
Dim model As NetworkModel = _modelList.FirstOrDefault(Function(m) m.Id = 1001)
If model IsNot Nothing Then . . . . .
I know that it is not possible to get keys (How to get the Key and Value from a Collection VB.Net) and it is better to use other classes. However I am debugging 10 years old code and I cannot change it.
In the Watch Window I see:
So it seems to be possible to deal the collection as "List(of KeyValuePair)". Can I do it in code or is it only an internal translation.
I basically need to list all KEYs in a Collection.
VisualBasic.Collection has an undocumented private method InternalItemsList which allows reading keys besides values. The type of InternalItemsList is Microsoft.VisualBasic.Collection.FastList which does not seem to be Enumerable but has a method Item which returns items with a zero based index. The type of those items is Microsoft.VisualBasic.Collection.Node. An item has two private properties m_Value and m_Key. And here we are.
Following code illustrates how to convert VisualBasic.Collection to List(Of KeyValuePair.
Dim flg As BindingFlags = BindingFlags.Instance Or BindingFlags.NonPublic
Dim InternalList As Object = col.GetType.GetMethod("InternalItemsList", flg).Invoke(col, Nothing)
Dim res As New List(Of KeyValuePair(Of String, Object))
For qq As Integer = 0 To col.Count - 1
Dim Item As Object = InternalList.GetType.GetProperty("Item", flg).GetValue(InternalList, {qq})
Dim Key As String = Item.GetType.GetField("m_Key", flg).GetValue(Item)
Dim Value As Object = Item.GetType.GetField("m_Value", flg).GetValue(Item)
res.Add(New KeyValuePair(Of String, Object)(Key, Value))
Next
I know that using undocumented functions is not safe but it is for internal use only and only solution I have managed to find.
I have a List(Of String) object and need to create a new collection based on the strings' values. The new collection will be of a custom class with two string fields - call them Key and Value (but it's not the built-in KeyValue class, it's a custom class).
All the values of Key will be the same, it's just Value that I want to source from the string list. Example:
Dim slValues = New List(Of String)({"Cod", "Halibut", "Herring"})
Dim myList = New List(Of myClass)( ... amazing initialisation line here? )
Class myClass
Public Key As String ' This will always be "Fish"
Public Value As String ' This will be the fish name.
End Class
(Note I don't actually have access to the class I'm using, so can't just change it to Public Key As String = "Fish" as a default. Key must be set at runtime.)
I can of course just do a loop and do it manually, but I'm wondering if there's a whiz-bang way to achieve this as part of the initialisation line?
How about this
Dim myList = slValues.ConvertAll(Of myClass)( _
Function(s) New YourClass With {.Key = "Fish", .Value = s})
Here's an alternative to Jodrell's answer using Linq's Select function:
Dim myList = slValues.Select(Function(fish) New CustomClass With {.Key = "Fish", .Value=fish}).ToList()
from x in Enumerable.Range(1, slValues.count-1).ToArray
select new KeyValuePair(of string,myClass) with {.Key=slValues(x),.Value=myList(x)}
hope it helps.
OK, that question sounds maybe a little confusing so I'll try to explain it with an example.
Pretend you have an object like this:
Class Something
Private varX As New Integer
Private varY As New String
'[..with the associated property definitions..]
Public Sub New()
End Sub
End Class
And another with:
Class JsonObject
Inherits Dictionary(Of String, String)
Public Function MakeObject() As Object 'or maybe even somethingObject
Dim somethingObject As New Something()
For Each kvp As KeyValuePair(Of String, String) In Me
'Here should happen something to use the Key as varX or varY and the Value as value for the varX or varY
somethingObject.CallByName(Me, kvp.Key, vbGet) = kpv.Value
Next
return somethingObject
End Function
End Class
I've got the 'CallByMe()' function from a previous question of myself
CallByName works different from the way you are trying to use it. Look at the documentation, it will tell you that in this particular case the correct usage would be
CallByName(Me, kvp.Key, vbSet, kpv.Value)
However, the function CallByName is part of a VB library that isn’t supported on all devices (notably it isn’t included in the .NET Mobile framework) and consequently it’s better not to use it.
Using proper reflection is slightly more complicated but guaranteed to work on all platforms.
Dim t = GetType(Something)
Dim field = t.GetField(kvp.Key, BindingFlags.NonPublic Or BindingFlags.Instance)
field.SetValue(Me, kvp.Value)
I have a 3rd party method that returns an old-style ArrayList, and I want to convert it into a typed ArrayList(Of MyType).
Dim udc As ArrayList = ThirdPartyClass.GetValues()
Dim udcT AS List(Of MyType) = ??
I have made a simple loop, but there must be a better way:
Dim udcT As New List(Of MyType)
While udc.GetEnumerator.MoveNext
Dim e As MyType = DirectCast(udc.GetEnumerator.Current, MyType)
udcT.Add(e)
End While
Dim StronglyTypedList = OriginalArrayList.Cast(Of MyType)().ToList()
' requires `Imports System.Linq`
Duplicate.
Have a look at this SO-Thread: In .Net, how do you convert an ArrayList to a strongly typed generic list without using a foreach?
In VB.Net with Framework < 3.5:
Dim arrayOfMyType() As MyType = DirectCast(al.ToArray(GetType(MyType)), MyType())
Dim strongTypeList As New List(Of MyType)(arrayOfMyType)
What about this?
Public Class Utility
Public Shared Function ToTypedList(Of C As {ICollection(Of T), New}, T)(ByVal list As ArrayList) As C
Dim typedList As New C
For Each element As T In list
typedList.Add(element)
Next
Return typedList
End Function
End Class
If would work for any Collection object.
I would like to point out something about both the DirectCast and System.Linq.Cast (which are the same thing in the latest .NET at least.) These may not work if the object type in the array is defined by the user class, and is not easily convertable into object types that .NET recognizes. I do not know why this is the case, but it seems to be the problem in the software for which I am developing, and so for these we have been forced to use the inelegant loop solution.