I am attempting to migrate a legacy vb.net application to .net standard and turn it into a nuget package. A good amount of it has been straight forward. I am currently hung up on this error caused by functions like this.
Public Property ErrorMessages As Collection
Get
ErrorMessages = _errorMessages
End Get
Set(value As Collection)
_errorMessages = value
End Set
End Property
If i import System.Collections.ObjectModelCollection(Of T) it is asking me for a type and i am unsure how to proceed. It turns my code into
Collection(Of,) and expects a second argument. Has anyone faced this before? Do i use a different import statement or how is this dealt with in vb now?
You should almost certainly replace Collection with Dictionary(Of TKey, TValue), using the dictionary type from the System.Collections.Generic namespace.
Once again, this requires you to fill in the genetic type arguments TKey and TValue with the actual types. You need to figure out from context which type fits the collection. The value of TKey is probably String since that’s the only key type VB6’ collections properly support. And given the name (ErrorMessages), TValue is probably String as well.
Related
I am struggling. Got properties that are of type ISet(of String) and I need to assign them with value.
.Add()
throws empty link error since it is not instantiated, been trying to create an instance, assign value and pass with set(), but
Activator.CreateInstance(Type.GetType(MyClass.MyProperty)
throws empty link. Neither this solution Visual Basic: dynamically create objects using a string as the name works, I ve output the list and ISet is simply not there.
I've been trying to solve this for a while now.
Interfaces don't fully define objects. They only define one part of an object, and therefore you don't have enough information from the ISet(Of String) interface on it's own to create an instance.
What you need to do is find a type that implements the interface, and create one of those... HashSet(Of String) and SortedSet(Of String) would both work.
So we recently migrated an application from .NET 1.1 to .NET 4.0.
And with that, there was a bunch of compatibility issues which we had to fix.
One of them is that a block of code is throwing the InvalidOperationException.
Public Function MyFunction(ByVal Params As myParams, ByVal ParamArray someNumber As Integer()) As myData
...
If someNumber.BinarySearch(options, MyEnum.Something) >= 0 Then
...
EndIf
...
EndFunction
Before we migrated to .NET4 this was working correctly in .NET1. Now based on some threads i've been reading, there has been reports about this problem which was fixed in .NET4.5. And that to fix this in my current version, I have to implement the IComparable interface on all elements of the array.
How do I go about to fixing this? I would appreciate any help and pointer. Thanks!
EDIT: Adding the link to the BinarySearch method we are using in the code. https://msdn.microsoft.com/en-us/library/y15ef976.aspx
Add Implements IComparable IComparable Interface to your class definition. 2. Add a method for IComparable.CompareTo to the class. Borrowing from msdn:
Public Class Temperature
Implements IComparable
' The temperature value
Protected temperatureF As Double
Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
Implements IComparable.CompareTo
If obj Is Nothing Then Return 1
Dim otherTemperature As Temperature = TryCast(obj, Temperature)
If otherTemperature IsNot Nothing Then
Return Me.temperatureF.CompareTo(otherTemperature.temperatureF)
Else
Throw New ArgumentException("Object is not a Temperature")
End If
End Function
....
End Class
Of coarse the code in the CompareTo function depends on your class (you didn't provide much to go on). All numeric types (such as Int32 and Double) implement IComparable, as do String, Char, and DateTime. Custom types should also provide their own implementation of IComparable to enable object instances to be ordered or sorted. I believe that might be the situation in your case. I hope this helps.
Try this:
...
Array.Sort(Of Integer)(someNumber) ' only if someNumber is not previously sorted
If Array.BinarySearch(Of Integer)(someNumber, MyEnum.Something) >= 0 Then
...
End If
...
This should work in all .NET frameworks > 2.0.
How do I go about to fixing this?
You are not using it correctly. BinarySearch is a Shared/static method and doesnt show in Intellisense when trying to use it as an instance method:
If you type it in anyway, you get a new compiler warning: Access of shared member ... through an instance ... will not be evaluated. MSDN doesnt have anything for NET 1.1, so I dont know if it changed since then (doubtful). Correct usage:
IndexOf6 = Array.BinarySearch(myIntAry, 6)
Which begs the question, as part of the conversion from NET 1.x to 4.5, why not convert this to List(Of Int32). A quick test shows that the IndexOf() method is 2-3 times faster:
IndexOf6 = intList.IndexOf(6)
The List<T> method is also more 'standalone' since unlike a System.Array, it need not be sorted in order to work.
is something like this possible - and if so how?
Public Sub CreateGenericList(ByVal SampleObject As Object)
Dim genericList as new List(Of SampleObject.GetType())
End Function
I want to create a class that is able to deserialize a given XML-file.
The XML-file contains serialized values of a custom type, which is unknown at compilation time.
I thought it might be possible to just initialize the class with a parameter SampleObject and to then get that SampleObject's type for all further progressing.
But it seems as if the type for all operations has to be known at compilation time?
Is there a way around it or can you explain the problem to me?
The code example above is just to illustrate my problem
Thanks for the help,
Janis
Edit: Your answers might allready have solved the problem, I will read more on the topics "reflection" and "generics" and keep you up to date if i make any progress. So thanks allot for the help.
For those still interested:
I was asked for the purpose of my question and will try to explain it as best i can.
Public Function ReadAllObjects() As List(Of myObjectType)
Dim result As New List(Of myObjectType)
Dim ObjectSerializer As New System.Xml.Serialization.XmlSerializer(result.GetType)
Dim FileReader As New System.IO.FileStream(My.Settings.XMLPath, System.IO.FileMode.Open)
result = TryCast(ObjectSerializer.Deserialize(FileReader), List(Of myObjectType))
FileReader.Close()
RaiseEvent ReadingFinished()
Return result
End Function
This pretty much sums up what I want to create: A EasyXmlHandling.dll for further use, which will be initialized with the currently used variable type.
It is then supposed to be able to write and read from/to an XML-File in a really easy way, by just calling "ReadAllObjects" (returns a List of myObjectType) or "AddObject(ByVal theNewObject)"... (more functions)
I got all that to work with a custom class as type, so i could now easily re-use the EasyXmlHandling-code by just replacing that type in the sourcecode with whatever new class i will want to use.
I though would prefer to just call the .dll with a sample object (or the type of it) and to have it do everything else automaticly.
I hope that was understandable, but neither my english nor my technical vocabulary are really good ;)
So thanks again for the help and for reading through this.
I will try to get it to work with all your previous answers and will update the topic when i make further progress.
No, that is not possible (at least, not without using reflection). The whole point of specifying the type in a generic list, or any other generic type, is so that the compiler can perform compile-time type checking. If you aren't specifying the type at compile-time, there is no benefit to it at all. Beyond there being no benefit, it's also simply not supported. If you don't know the type at compile time, you should just use Object instead, since that will work with objects of any type, for instance:
Dim myList As New List(Of Object)()
If you need a list, however, which only allows one type of item, but that type is unknown at compile time, that is possible to do, but you would probably need to create your own non-generic list class for something like that. As far as I know, there is no non-generic list class provided in the framework which restricts its items to a single specified type.
Update
Now that you've explained your reason for doing this, it's clear that generics are your solution. For instance, you could implement it as as generic function, like this:
Public Function ReadAllObjects(Of T)() As List(Of T)
Dim result As New List(Of T)
Dim ObjectSerializer As New System.Xml.Serialization.XmlSerializer(result.GetType)
Dim FileReader As New System.IO.FileStream(My.Settings.XMLPath, System.IO.FileMode.Open)
result = TryCast(ObjectSerializer.Deserialize(FileReader), List(Of T))
FileReader.Close()
RaiseEvent ReadingFinished()
Return result
End Function
Then, you could call it, like this, passing it which ever type you want:
Dim cars As New List(Of Car) = ReadAllObjects(Of Car)()
Dim boats As New List(Of Boat) = ReadAllObjects(Of Boat)()
As you can see, that is the whole purpose of generics. They are a very powerful tool when you any to keep your code type-specific, but still be able to re-use it with different types. Reflection, on the other-hand is not a good fit in this particular situation. Reflection is also very useful, but should always be considered an option of last resort. If there is another way to do it, without reflection, that's usually the better way.
I need to create a property in a class that will give the programmer a list of values to choose from. I have done this in the past using the enums type.
Public Enum FileType
Sales
SalesOldType
End Enum
Public Property ServiceID() As enFileType
Get
Return m_enFileType
End Get
Set(ByVal value As enenFileType)
m_enFileType = value
End Set
End Property
The problem is I would like to populate the list of values on init of the class based on SQL table values. From what I have read it is not possible to create the enums on the fly since they are basically constants.
Is there a way I can accomplish my goal possibly using list or dictionary types?
OR any other method that may work.
I don't know if this will answer your question, but its just my opinion on the matter. I like enums, mostly because they are convenient for me, the programmer. This is just because when I am writing code, using and enum over a constant value gives me not only auto-complete when typing, but also the the compile time error checking that makes sure I can only give valid enum values. However, enums just don't work for run-time defined values, since, like you say, there are compile time defined constants.
Typically, when I use flexible values that are load from an SQL Table like in your example, I'll just use string values. So I would just store Sales and SalesOldType in the table and use them for the value of FileType. I usually use strings and not integers, just because strings are human readable if I'm looking at data tables while debugging something.
Now, you can do a bit of a hybrid, allowing the values to be stored and come from the table, but defining commonly used values as constants in code, sorta like this:
Public Class FileTypeConstants
public const Sales = "Sales"
public const SalesOldType = "SalesOldType"
End Class
That way you can make sure when coding with common values, a small string typo in one spot doesn't cause a bug in your program.
Also, as a side note, I write code for and application that is deployed internally to our company via click-once deployment, so for seldom added values, I will still use an enum because its extremely easy to add a value and push out an update. So the question of using and enum versus database values can be one of how easy it is to get updates to your users. If you seldom update, database values are probably best, if you update often and the updates are not done by users, then enums can still work just as well.
Hope some of that helps you!
If the values aren't going to change after the code is compiled, then it sounds like the best option is to simply auto-generate the code. For instance, you could write a simple application that does something like this:
Public Shared Sub Main()
Dim builder As New StringBuilder()
builder.AppendLine("' Auto-generated code. Don't touch!! Any changes will be automatically overwritten.")
builder.AppendLine("Public Enum FileType")
For Each pair As KeyValuePair(Of String, Integer) In GetFileTypesFromDb()
builder.AppendLine(String.Format(" {0} = {1}", pair.Key, pair.Value))
End For
builder.AppendLine("End Enum")
File.WriteAllText("FileTypes.vb", builder.ToString())
End Sub
Public Function GetFileTypesFromDb() As Dictionary(Of String, Integer)
'...
End Function
Then, you could add that application as a pre-build step in your project so that it automatically runs each time you compile your main application.
I am attempting to create a generic function that the students in my introductory VB .NET course can use to search a single dimension array of a structure.
My structure and array look like this:
Private Structure Survey
Dim idInteger As Integer
Dim membersInteger As Integer
Dim incomeInteger As Integer
Dim stateString As String
Dim belowPovertyLevelBoolean As Boolean
End Structure
Private incomeSurvey(199) As Survey
My generic function header looks like:
Private Function FindSurveyItem(Of xType As Structure)
(ByVal surveyIDInInt As Integer, ByVal surveyArrayIn() As xType) As Integer
??????
End Function
My call to the function looks like:
If FindSurveyItem(Of Survey)(CInt(idTextBox.Text), incomeSurvey) <> -1 Then
My question is: Is there a way to reference the individual structure fields in the array from inside the function? I was trying to make it generic so that the student could simply pass their array into the function - their structure may be named differently than mine and the field names may be different.
I suspect there are other ways to deal with this situation, but I was trying to keep it to just a simple single-dimension array of a structure. I don't think it is possible to do what I want, but I wondered what others thought.
Is there a way to reference the individual structure fields in the array from inside the function?
Generic instead of an array you need a collection type. Add LINQ Code:
Dim Surveys = From svys In xType
Where svys.idInteger = surveyIDInInt
Select svys
For Each rSurveys In svys
'''' Your Code
Next
This is rough answer fill in the details (I know imagine LINQ without SQL DB!!)
If you have a genric type parameter T you are only able to access members of instances of T that are known to exist at compile time. As every type derives from Object you have only the members of Object availiable - ToString(), GetType(), GetHashCode(), and Equals().
If you want to access other members you have to constrain what T is allowed to be. In your situation a interface would be the way to go. See MSDN for details.
You could also try to use reflection or check the actual type at runtime an perform a cast. The first is hard to impossible to do if you do not know much about the types you will get. And the later requires you to know possible types at compiletime and will not work in your situation, too.
Another way might be to pass a delegate to the search method that performs the actual comparison.
What you're looking for are predicates, if using ,net 3.5
dim arr() as structure
Array.Find(arr, function(item)(item.MyMember = MemberToMatch))
More combersome in earlier versions, see here for more info
The point being, that your function would look very like an implementation of Array.Find (if you didn't want to use the function provided), and the students would need to write their own predicate function.
No, there isn't. You can't know the type at compile time, therefore you cannot access members of that type. You would need change from a structure to a class that must implement IComparable so that you can use CompareTo between the item you pass in and the array you are passing in.
Though it's not entirely clear what you are trying to do within your method so I'm guessing by the name of the method.
You can use reflection to get those fields, but in this case that wouldn't have much meaning. How would you know that the passed type has the field you're looking for? There are other problems with that code as well.
Instead, to do this I would normally create an interface for something like this that had a public ID property, and constrain my input to the function to implement that interface, or as others mentioned use a built-in feature in the clr.
But that may be ahead of where your students are. If you just want an example of a generic function, my suggestion is to show them a type-safe implementation of the old vb imediate if function:
Public Function IIf(Of T)(ByVal Expression As Boolean, ByVal TruePart As T, ByVal FalsePart As T) AS T
If Expression Then Return TruePart Else Return FalsePart
End Function
Note that this is obsolete, too, as in VS2008 and beyond you can use the new If operator instead, which will work better with type inference and won't try to evaluate the expression that isn't returned.