How do I...

[Bryan Dickerson]

I have a simple list box that I want to show a list of names and also I want
to store in the list box an id, just a string value, so that when the user
clicks on a name I can use the id to get information about that name. I
know how I would do it in VB6 (using the Tag property). Is there a better
way to do it in VB.Net?

 

[Herfried K. Wagner [MVP]]

I have a simple list box that I want to show a list of names and also I
want to store in the list box an id, just a string value, so that when the
user clicks on a name I can use the id to get information about that name.

\\\
Dim p As New Person()
p.Name = "Pink Panther"
p.Age = 22
Me.ComboBox1.Items.Add(p)

' Test.
MsgBox(DirectCast(Me.ComboBox1.Items(0), Person).ToString())
..
..
..
Public Class Person
Private m_Name As String
Private m_Age As Integer

Public Property Name() As String
Get
Return m_Name
End Get
Set(ByVal Value As String)
m_Name = Value
End Set
End Property

Public Property Age() As Integer
Get
Return m_Age
End Get
Set(ByVal Value As Integer)
m_Age = Value
End Set
End Property

Public Overrides Function ToString() As String
Return Me.Name & " (" & Me.Age.ToString() & ")"
End Function
End Class
///

Alternatively, you can use a bound combobox:

\\\
With Me.ListBox1

' This can be an 'ArrayList' or array too, for example.
.DataSource = Database.FindPeople(...)
.DisplayMember = "Name"
.ValueMember = "Age"
End With
///

 

[Bryan Dickerson]

When I do the Items.Add(object), how does the Listbox/Combobox know what
property to display?

 

[Herfried K. Wagner [MVP]]

When I do the Items.Add(object)

Use it if you want to add an object to the listbox.

how does the Listbox/Combobox know what property to display?

The listbox will display the value returned by the object's 'ToString'
method.

 

[Bryan Dickerson]

That would be great except that the object that I'm Adding to the listbox is
a DataRow. Can I override just a ToString method of that? If so, how?

 

[Cor Ligthert]

Bryan,

That would be great except that the object that I'm Adding to the listbox
is a DataRow. Can I override just a ToString method of that? If so, how?

I doubt that, are you not binding a datatable or its defaultview or a
created dataview .

And than set the display and valuemember of those in the listboxbox?.

myListbox.datasource = mytable.defaultview 'although this defaultview is
overdone
myListbox.displaymember = "MyColumn1"
myListbox.displaymember = "MyColumn2"

I hope this helps,

Cor

 

[Bryan Dickerson]

Please bear with me as I'm trying very hard to learn, but do I 'set' the
DefaultView or is it pre-set? If I can set it, how do I do it?

 

[Cor Ligthert]

Bryan,

It was confusing for me as well in the beginning.

Every datatable holds a dataview which is named the defaultview.
However you can use it to set by instance the sort order of a datatable in a
dataview

dt.defaultview.sort = "MySortColumn"

is the same as
dim dv as dataview = dt.defaultview
dv = "MySortColumn"
(and use than dv)

div dv as new dataview(dt)
dv = "MyOtherSortColumn"

Means that you use an extra dataview and can show the datatable on two
different controls in two different sort orders

I hope that this gives an idea

Cor

 

[Bryan Dickerson]

Ok, how do I specify which columns to include in the DataView? Oh, and
thanks for your patience with me!

 

[Cor Ligthert]

Bryan,

Now you come in my eyes with a complete different question.

A defaultview and a dataview have a view on the complete table although
there is a rowfilter for showing.

This means as well all columns there is no column filter.

However there are a lot of way to choose the value from a column that you
want to use, and the other use use not.

I hope this helps,

Cor

 

[Bryan Dickerson]

I'm sorry but you lost me and my questions seem to be leading in the wrong
direction or leading off on unimportant tangents. If I have a simple
Dataset object, can I choose which columns make up a DataView or the
DefaultView? Or do all the columns in the Dataset automatically become part
of the dataview?

 

[Cor Ligthert]

Bryan,

I'm sorry but you lost me and my questions seem to be leading in the wrong
direction or leading off on unimportant tangents. If I have a simple
Dataset object, can I choose which columns make up a DataView or the
DefaultView? Or do all the columns in the Dataset automatically become
part of the dataview?

I cannot answer this with yes or no because a defaultview is not direct
related to a dataset.
(Maybe helps this to become out of your confusion. A dataset is absolute not
the same as a recordset, A datatable looks a little bit as a recordset).

Dataset has a collection of datatables
DataTable as a collection of (data)columns and datarows
Datarow has a collection of Items which are described in the (data)columns

A datatable has integrated a dataview, which tells in what order or with
what filter they shoud be showed in complex controls.

Therefore in your problem where you have a Listbox you can go back to my
sample

myListbox.datasource = mytable
myListbox.displaymember = "MyColumn1"
myListbox.displaymember = "MyColumn2"

This shows a listbox with the text from Mycolumn1 from the table mytable.

Some people write this as well like this
dim dv as DataView = myTable.defaultview
or
dim dv as New Dataview(myTable) 'this creates a new dataview

Than the rest stays the same
myListbox.datasource = dv
myListbox.displaymember = "MyColumn1"
myListbox.displaymember = "MyColumn2"

What is for the rest in the table is not important for your problem.

I hope this helps,

Cor