How do I sort an ArrayList of objects by a property value

[Paulers]

Hello I have an ArrayList full of Person objects. I would like to sort
the object array by the objects property 'Name' so when I loop through
it and populate a combobox they are in order. How do I attack something
like this? Any help is greatly appreciated.

thanks!

[hoppy]

Re: How do I sort an ArrayList of objects by a property value

"Paulers" <SuperGh0d@gmai l.comwrote in
news:1167350973 .191094.3620@48 g2000cwx.google groups.com:

Hello I have an ArrayList full of Person objects. I would like to sort
the object array by the objects property 'Name' so when I loop through
it and populate a combobox they are in order. How do I attack
something like this? Any help is greatly appreciated.
>
thanks!
>
>

Make the person class implement the IComparable interface, Write code
for the Compare method that appears. Then it will all magically work
when you call the sort method. If this is a 2005 version then you can
use IComparable(Of Person). And use a list(Of Person) instead of
arraylist too!

If you have 2003, then change this to plain IComparable. The parameter
of the Compare method will be an object, so cast it to Person.

Public Class Person
Implements IComparable(Of 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

' called by the arraylist.sort method.
Public Function CompareTo(ByVal other As Person) As Integer _
Implements System.ICompara ble(Of Person).Compare To
' Compare this ones name with the other ones name.
' return <0 if this one comes first,
' 0 if they are equal,
' >0 if the other one comes first.
' String.Compare does this anyway
Return String.Compare( Me.Name, other.Name)
End Function
End Class

[=?Utf-8?B?S2VycnkgTW9vcm1hbg==?=]

RE: How do I sort an ArrayList of objects by a property value

Paulers,

One way is to have your Person class implement IComparable.Com pareTo. For
Example:

Public Class Person
Implements IComparable

Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
Implements IComparable.Com pareTo

Dim person As Person = DirectCast(obj, Person)

If Me.Name < person.Name Then
Return -1
ElseIf Me.Name = person.Name Then
Return 0
Else
Return 1
End If
End Function

Then, when you call the arraylist's Sort method, the objects will be sorted
by Name.

"Paulers" wrote:

Hello I have an ArrayList full of Person objects. I would like to sort
the object array by the objects property 'Name' so when I loop through
it and populate a combobox they are in order. How do I attack something
like this? Any help is greatly appreciated.
>
thanks!
>
>

[Herfried K. Wagner [MVP]]

Re: How do I sort an ArrayList of objects by a property value

"Paulers" <SuperGh0d@gmai l.comschrieb:

Hello I have an ArrayList full of Person objects. I would like to sort
the object array by the objects property 'Name' so when I loop through
it and populate a combobox they are in order. How do I attack something
like this?

<URL:http://dotnet.mvps.org/dotnet/samples/techniques/CompareOperator .zip>

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[=?Utf-8?B?QWxpZW4yXzUx?=]

RE: How do I sort an ArrayList of objects by a property value

Here's how I've done it.. If ArrayList implements the IBindingList interface
you can use something like this... If it doesn't you can implement the
IBindingList interface in one of your base classes, if you want an example of
how to do that look at Rocky Lhotka's CSLA object framework, it's open
source... Or just use his base classes, it takes a little bit more time to
implement but it's worth it with the funtionality you achieve by doing so,
there's also some code generation tools that make generating these object
hiearchies trivial..

Public WriteOnly Property Sort() As String

Set(ByVal Value As String)
Dim str() As String = Split(Value, " ")
Dim mSortPropertyNa me As String = "", mSortDirection As String =
""

'parse the input string
If str.Length = 1 Then 'direction not specified, use default
mSortPropertyNa me = str(0).Trim
ElseIf str.Length = 2 Then
mSortPropertyNa me = str(0).Trim & ""
mSortDirection = str(1).Trim & ""
Else
Throw New ApplicationExce ption("Too many parameters
specified for the sort.")
End If
Dim childType As Type = GetType(Me)
Dim mSortProperty As PropertyDescrip tor = _

TypeDescriptor. GetProperties(c hildType).Item( mSortPropertyNa me)
Select Case mSortDirection. ToUpper.Trim
Case Is = "DESC"
DirectCast(Me, IBindingList).A pplySort(mSortP roperty,
ListSortDirecti on.Descending)
Case Is = "ASC"
DirectCast(Me, IBindingList).A pplySort(mSortP roperty,
ListSortDirecti on.Ascending)
Case Else
DirectCast(Me, IBindingList).A pplySort(mSortP roperty,
ListSortDirecti on.Ascending)
End Select
End Set
End Property


HTH

"Paulers" wrote:

Hello I have an ArrayList full of Person objects. I would like to sort
the object array by the objects property 'Name' so when I loop through
it and populate a combobox they are in order. How do I attack something
like this? Any help is greatly appreciated.
>
thanks!
>
>

[Chris Dunaway]

Re: How do I sort an ArrayList of objects by a property value

Kerry Moorman wrote:

One way is to have your Person class implement IComparable.Com pareTo. For
Example:
>
Public Class Person
Implements IComparable
>
Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
Implements IComparable.Com pareTo
>
Dim person As Person = DirectCast(obj, Person)
>
If Me.Name < person.Name Then
Return -1
ElseIf Me.Name = person.Name Then
Return 0
Else
Return 1
End If
End Function
>
Then, when you call the arraylist's Sort method, the objects will be sorted
by Name.

Assuming the Name property is a String, you can shorten that code to
this:

Public Class Person
Implements IComparable

Public Overloads Function CompareTo(ByVal obj As Object) As Integer
_
Implements IComparable.Com pareTo

Dim person As Person = DirectCast(obj, Person)

Return Me.Name.Compare To(person.Name)

End Function

[Chris Dunaway]

Re: How do I sort an ArrayList of objects by a property value

Kerry Moorman wrote:

Chris,
>
That's really nice. I had not noticed that CompareTo method of a string.
>

That should work for all primitive types. Of course if you have custom
comparison logic, such as last name AND first name, then you would have
to implement like you showed.

Cheers!

Chris

[Paulers]

Re: How do I sort an ArrayList of objects by a property value

Thanks everyone! I really appreciate your help.
Chris Dunaway wrote:

Kerry Moorman wrote:

Chris,

That's really nice. I had not noticed that CompareTo method of a string.

>
That should work for all primitive types. Of course if you have custom
comparison logic, such as last name AND first name, then you would have
to implement like you showed.
>
Cheers!
>
Chris