I created a datatable containing the list of notes for songs:
Private Table As New DataTable
Public Sub New()
With Table
.Columns.Add("Name")
.Columns.Add("NoteList")
.Rows.Add("GOT", GOT)
.Rows.Add("Yesterday", Yesterday)
End With
End Sub
GOT and Yesterday are lists of notes (notes is a class containing note, duration etc..)
On the form I then assign the datatable to a combobox:
ComboSongs.DisplayMember = Songs.DataTable.Columns(0).ColumnName
ComboSongs.ValueMember = Songs.DataTable.Columns(1).ColumnName
ComboSongs.DataSource = Songs.DataTable
I try to get the list of notes like this:
Dim songToPlay As List(Of Note) = CType(ComboSongs.SelectedValue, List(Of Note))
When I try to get the list I get the error:
System.InvalidCastException: 'Unable to cast object of type 'System.String' to type 'System.Collections.Generic.List`1[test.Note]'.'
Now I am unsure where I am getting it wrong. What would be the correct way to do this?
Your ValueMember is what is returned through the ComboBox.SelectedValue. So since you set the ValueMember like this
ComboSongs.ValueMember = Songs.DataTable.Columns(1).ColumnName
you only get the ColumnName. I assume that's a string and, well, the error message tells you it is one
... Unable to cast object of type 'System.String' ...
I guess that should be "NoteList", since that would be returned by Songs.DataTable.Columns(1).ColumnName
But this all doesn't make much sense, as I guess you are selecting a song there, either "Yesterday" or "GOT". At the point you're at it's so convoluted to return the DataTable rows, and index them. You will need to find the row by name and that is just too complicated when you could just create a class with strong names. I'll give you a class based solution but I'm not sure if you can make that change.
Private Class Song
Public Property Name As String
Public Property NoteList As List(Of Note)
End Class
Private Class Note
' your implementation
End Class
Dim songs As New List(Of Song)()
songs.Add(New Song() With {.Name = "GOT", .NoteList = New List(Of Note)})
songs.Add(New Song() With {.Name = "Yesterday", .NoteList = New List(Of Note)})
' need to populate those NoteLists first
ComboSongs.DisplayMember = "Name"
ComboSongs.DataSource = songs
Dim songToPlay = songs.SingleOrDefault(Function(s) s.Name = ComboSongs.SelectedValue)
Dim noteList = songToPlay.NoteList
Related
i have a list(of custom class)
and i want to extract a list of all 'name' String, from it, through linq
I know how to do with a loop, but i need to get it with a linear, brief linq instruction.
i've checked this help
C# Extract list of fields from list of class
but i have problem in linq correct syntax
in particular because i would like to extract a New List(Of String)
Class Student
Sub New(ByVal NewName As String, ByVal NewAge As Integer)
Name = NewName
Age = NewAge
End Sub
Public Name As String
Public Age As Integer
End Class
Public Sub Main
Dim ClassRoom as New List(Of Student) From {New Student("Foo",33), New Student("Foo2",33), New Student("Foo3",22)}
Dim OneStudent as Student = ClassRoom(0)
Dim AllStudentsNames As New List(Of String) From {ClassRoom.Select(Function(x) x.Name <> OneStudent.Name).ToList}
End Sub
But something wrong...
Any help?
P.S. Since c# it's close to vb.Net, also c# helps are well welcome.
First, you don't need to create a new list From the one returned by the LINQ method. It's already in a new list at that point, so you can just set AllStudentsNames equal directly to what the ToList method returns.
Second, you are not selecting the name. You are selecting the result of the equality test to see if the names are different. In other words, when you say Select(Function(x) x.Name <> OneStudent.Name), that returns a list of booleans, where they true if the names are different and false if the names are the same. That's not what you want. You want the list of names, so you need to select the name.
Third, if you need to filter the list so that it only returns ones where the name is different, then you need to add a call to the Where method.
Dim AllStudentsNames As List(Of String) = ClassRoom.
Where(Function(x) x.Name <> OneStudent.Name).
Select(Function(x) x.Name).
ToList()
I have read some threads about this "error" but I can't figure out how to solve my problem.
I have a class that looks something like this:
Public Class Person
Public Property Name As String
Public Property PhoneNumber As string
Public Property Age As Integer
Public sub New(ByVal Values As String())
Me.Name = Values(0)
Me.PhoneNumber = Values(1)
Me.Age = Convert.ToInt32(Values(2))
End Sub
End Class
I get my data from a semicolon separated file, and i create a list of Person objects by looping this file and split on semicolon. Like this
Dim PersonsList As New List(Of Person)
For Each line in textfile..........
PersonsList.Add(New Person(line.Split(";")))
Next
When the list is complete, I tell my DataGridView that DataSource is PersonsList.
This works like a charm, but I'm not able to sort the columns.
I found this post amongst many (where the class values are not properties, which mine are) and tried that converting function which did'nt really work in my case. The right amount of rows were created, but all of the columns were blank.
What am I missing?
If you use a datatable as the data source, column sorting is automatically enabled and you can sort the data by any column:
Dim dt As New DataTable
dt.Columns.AddRange(
{
New DataColumn("Name"),
New DataColumn("Phone"),
New DataColumn("Age")
})
For Each s As String In IO.File.ReadAllLines("textfile1.txt")
Dim temprow As DataRow = dt.NewRow
temprow.ItemArray = s.Split(";"c)
dt.Rows.Add(temprow)
Next
DataGridView1.DataSource = dt
I'm trying to use a generic list without knowing the type when loading the page. I have a typePropertyCollection which inherits from List(Of PropertyData). The usercontrol that uses this collection doesn't know what type of data is used (which objects). So when the page is loaded, I pass along the type to the usercontrol using a dependencyproperty. This type ends up in this method:
Private Shared Sub OnObjectTypeChanged(ByVal obj As DependencyObject, ByVal args As DependencyPropertyChangedEventArgs)
Dim objectType As Type = TryCast(args.NewValue, Type)
Dim aList As List(Of PropertyData) = New TypePropertyCollection(Of objectType)
End Sub
I can succesfully retrieve the type from the EventArgs and put it in a variable. When I'm creating a new typePropertyCollection, I want to pass the type to the generic list, but it says the objectType isn't defined, although is is declared just the line above.
Any suggestions?
Edit
The class typepropertyCollection looks like this:
Public Sub New()
Dim properties = New List(Of PropertyInfo)(GetType(T).GetProperties(BindingFlags.Public Or BindingFlags.Instance))
For Each propertyToCheck In properties
Dim descriptionAttribute = propertyToCheck.GetCustomAttributes(GetType(DescriptionAttribute), True)
If Not descriptionAttribute Is Nothing AndAlso descriptionAttribute.Length > 0 Then
Add(New PropertyData() With {.Description = DirectCast(descriptionAttribute(0), DescriptionAttribute).Description, .PropertyName = propertyToCheck.Name})
Else
Add(New PropertyData() With {.Description = propertyToCheck.Name, .PropertyName = propertyToCheck.Name})
End If
Next
End Sub
To use this collection, I'm creating a new class which inherits from the typcollection:
Public Class CustomerTypePropertyCollection
Inherits TypePropertyCollection(Of Person)
End Class
I cannot do this because Person (I named it Person here to make it easier) is not known in that solution. It should also be possible to make collection of other types which or not known. That's why I wanted to pass the type of the object and use it that way.
Dim aList As List(Of PropertyData) = New TypePropertyCollection(Of Type)
This error is because you are attempting to create a TypePropertyCollection of Type 'objectType', objecttype is the variable name of a variable with a type of type .'. You would need a TypePropertyCollection of Type Type Type, not the variable name. Come back to me if there are other issues beyond this.
Rather than giving the very specific case (which I did earlier), let me give a general example. Let's say that I have a function, called callingFunction. It has one parameter, called parameter. Parameter is of an unknown type. Let us then say that I wish to copy this parameter, and return it as a new object. For example, in pseudo code, something along the lines of...
Function callingFunction(ByVal parameter As Object) As Object
Dim newObj As New Object
'newObj has the same value as parameter, but is a distinctly different object
'with a different reference
newObj = parameter
return newObj
End Function
EDIT: Additional Information
The first time I posted this question, I received only one response - I felt that perhaps I made the question too specific. I guess I will explain more, perhaps that will help. I have an ASP page with 10 tables on it. I am trying, using the VB code behind, to come up with a single solution to add new rows to any table. When the user clicks a button, a generic "add row" function should be called.
The difficulty lies in the fact that I have no guarantee of the contents of any table. A new row will have the same contents as the row above it, but given that there are 10 tables, 1 row could contain any number of objects - text boxes, check boxes, etc. So I want to create a generic object, make it of the same type as the row above it, then add it to a new cell, then to a new row, then to the table.
I've tested it thoroughly, and the only part my code is failing on lies in this dynamic generation of an object type. Hence why I asked about copying objects. Neither of the solutions posted so far work correctly, by the way. Thank you for your help so far, perhaps this additional information will make it easier to provide advice?
You can't do this in general. And it won't be a good idea, for example, if parameter is of a type which implements the singleton pattern. If parameter is of a type which supports copying, it should implement the ICloneable interface. So, your function could look like this:
Function MyFunc(ByVal parameter As Object) As Object
Dim cloneableObject As ICloneable = TryCast(parameter, ICloneable)
If Not cloneableObject Is Nothing Then
Return cloneableObject.Clone()
Else
Return Nothing
End If
End Function
You could implement something like this:
Dim p1 As Person = New Person("Tim")
Dim p2 As Object = CloneObject(p1)
Dim sameRef As Boolean = p2 Is p1 'false'
Private Function CloneObject(ByVal o As Object) As Object
Dim retObject As Object
Try
Dim objType As Type = o.GetType
Dim properties() As Reflection.PropertyInfo = objType.GetProperties
retObject = objType.InvokeMember("", System.Reflection.BindingFlags.CreateInstance, Nothing, o, Nothing)
For Each propertyInfo As PropertyInfo In properties
If (propertyInfo.CanWrite) Then
propertyInfo.SetValue(retObject, propertyInfo.GetValue(o, Nothing), Nothing)
End If
Next
Catch ex As Exception
retObject = o
End Try
Return retObject
End Function
Class Person
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Public Sub New()
End Sub
Public Sub New(ByVal name As String)
Me.Name = name
End Sub
End Class
Here's a simple class that will work for most objects (assumes at least .Net 2.0):
Public Class ObjectCloner
Public Shared Function Clone(Of T)(ByVal obj As T) As T
Using buffer As MemoryStream = New MemoryStream
Dim formatter As New BinaryFormatter
formatter.Serialize(buffer, obj)
buffer.Position = 0
Return DirectCast(formatter.Deserialize(buffer), T)
End Using
End Function
End Class
I am not sure how to phrase my question properly but I want to achieve something like this.
I have a class named Products
public class Products
private ID as Integer
private Name as String
Public Property ProductID()
Get
Return ID
End Get
Set(ByVal value)
ID = value
End Set
End Property
In one of my code behind pages, I am retrieving data from an SQL Command and placing the same into a datareader object.
How would I be able to declare the class so that each row in my datareader would actually be an instance of the said class?
Like for example:
Dim myProduct() as New Product
Dim intCnt as Integer
While datareaderData.read()
intCnt += 1
myProduct(intCnt) = new Product
myProduct(intCnt).ID = datareaderData("ID")
myProduct(intCnt).Name = datareaderData("Name")
End While
When I do the same, I am getting an error "Object Reference Not Set to an Instance of an Object.
I am quite stumped on this one. Any tips greatly appreciated. Thanks.
You should use an Arraylist or -better- a generic List(of Product).
Besides i would strongly recommend to set Option Strict On in your project's Compiler Settings.
Dim products As New List(Of Product)
While datareaderData.read()
Dim nextProduct As New Product
nextProduct.ProductID = CType(datareaderData("ID"), System.Int32)
nextProduct.Name = datareaderData("Name").ToString
products.add(nextProduct)
End While