IComparable<T>.CompareTo Method
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Compares the current object with another object of the same type.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Function CompareTo ( _
other As T _
) As Integer
int CompareTo(
T other
)
Parameters
- other
Type: T
An object to compare with this object.
Return Value
Type: System.Int32
A 32-bit signed integer that indicates the relative order of the objects being compared. The return value has the following meanings:
Value |
Meaning |
|---|---|
Less than zero |
This object is less than the other parameter. |
Zero |
This object is equal to other. |
Greater than zero |
This object is greater than other. |
Remarks
CompareTo provides a strongly typed comparison method for ordering members of a generic collection object. Because of this, it is usually not called directly from developer code. Instead, it is called automatically by the List<T>.Sort() method.
This method is only a definition and must be implemented by a specific class or value type to have effect. The meaning of the comparisons, "less than," "equal to," and "greater than," depends on the particular implementation.
By definition, any object compares greater than nulla null reference (Nothing in Visual Basic), and two null references compare equal to each other.
Notes to Implementers
For objects A, B, and C, the following must be true:
A.CompareTo(A) is required to return zero.
If A.CompareTo(B) returns zero, then B.CompareTo(A) is required to return zero.
If A.CompareTo(B) returns zero and B.CompareTo(C) returns zero, then A.CompareTo(C) is required to return zero.
If A.CompareTo(B) returns a value other than zero, then B.CompareTo(A) is required to return a value of the opposite sign.
If A.CompareTo(B) returns a value x that is not equal to zero, and B.CompareTo(C) returns a value y of the same sign as x, then A.CompareTo(C) is required to return a value of the same sign as x and y.
Notes to Callers
Use the CompareTo method to determine the ordering of instances of a class.
Examples
The following example illustrates the implementation of IComparable for an Address object. The example uses the generic List<T> object to create a collection of addresses. The List<T> object uses the IComparable<T> implementation to sort the list entries, which are then displayed in sorted order.
Public Class Address : Implements IComparable(Of Address)
Private addr1, addr2, cty, st, coun, postal As String
Public Sub New(address1 As String, address2 As String, city As String, _
state As String, postal As String, country As String)
Me.addr1 = address1
Me.addr2 = address2
Me.cty = city
Me.st = state
Me.coun = country
Me.postal = postalCode
End Sub
Public Property Address1 As String
Get
Return Me.addr1
End Get
Set
Me.addr1 = value
End Set
End Property
Public Property Address2 As String
Get
Return Me.addr2
End Get
Set
Me.addr2 = value
End Set
End Property
Public Property City As String
Get
Return Me.cty
End Get
Set
Me.cty = value
End Set
End Property
Public Property State As String
Get
Return Me.st
End Get
Set
Me.st = value
End Set
End Property
Public Property Country As String
Get
Return Me.coun
End Get
Set
Me.coun = value
End Set
End Property
Public Property PostalCode As String
Get
Return Me.postal
End Get
Set
Me.postal = value
End Set
End Property
Public Overrides Function ToString() As String
Return addr1 & vbCrLf & CStr(IIf(Not String.IsNullOrEmpty(addr2), addr2 & vbCrLf, "")) _
& cty & ", " & st & " " & postal & " " & coun
End Function
Public Function CompareTo(other As Address) As Integer _
Implements IComparable(Of Address).CompareTo
' If other is Nothing, this instance is greater.
If other Is Nothing Then Return 1
Dim otherAddress As String = other.Country & other.State & other.PostalCode & _
other.City & other.Address1 & other.Address2
Return (coun & st & postal & cty & addr1 & addr2).CompareTo(otherAddress)
End Function
End Class
Module Example
Public Sub Demo(outputBlock As System.Windows.Controls.TextBlock)
Dim addresses As New List(Of Address)
addresses.Add(New Address("106 East 5th St.", "", "New City", "MI", "48002", "USA"))
addresses.Add(New Address("47 East End Rd.", "", "Huxenplux", "NJ", "20203", "USA"))
addresses.Add(New Address("12043 N.E. 72nd St.", "", "Belleville", "WA", "98101", "USA"))
addresses.Sort()
For Each address As Address In addresses
outputBlock.Text &= address.ToString() & vbCrLf & vbCrLf
Next
End Sub
End Module
using System;
using System.Collections.Generic;
public class Address : IComparable<Address>
{
private string addr1, addr2, cty, st, coun, postal;
public Address(string address1, string address2, string city,
string state, string postalCode, string country)
{
this.addr1 = address1;
this.addr2 = address2;
this.cty = city;
this.st = state;
this.coun = country;
this.postal = postalCode;
}
public string Address1
{
get { return this.addr1; }
set { this.addr1 = value; }
}
public string Address2
{
get {return this.addr2; }
set { this.addr2 = value; }
}
public string City
{
get { return this.cty; }
set { this.cty = value; }
}
public string State
{
get { return this.st; }
set { this.st = value; }
}
public string Country
{
get { return this.coun; }
set { this.coun = value; }
}
public string PostalCode
{
get {return this.postal; }
set {this.postal = value; }
}
public override string ToString()
{
string addressLine2 = string.IsNullOrEmpty(addr2) ? "" : addr2 + "\n";
return addr1 + "\n" + addressLine2 +
cty + ", " + st + " " + postal + " " + coun;
}
public int CompareTo(Address other)
{
// If other is null, this instance is greater.
if (other == null) return 1;
string otherAddress = other.Country + other.State + other.PostalCode +
other.City + other.Address1 + other.Address2;
return (coun + st + postal + cty + addr1 + addr2).CompareTo(otherAddress);
}
}
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
List<Address> addresses = new List<Address>();
addresses.Add(new Address("106 East 5th St.", "", "New City", "MI", "48002", "USA"));
addresses.Add(new Address("47 East End Rd.", "", "Huxenplux", "NJ", "20203", "USA"));
addresses.Add(new Address("12043 N.E. 72nd St.", "", "Belleville", "WA", "98101", "USA"));
addresses.Sort();
foreach (Address address in addresses)
outputBlock.Text += address.ToString() + "\n\n";
}
}
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.