IComparable.CompareTo Method
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Compares the current instance with another object of the same type and returns an integer that indicates whether the current instance precedes, follows, or occurs in the same position in the sort order as the other object.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Function CompareTo ( _
obj As Object _
) As Integer
int CompareTo(
Object obj
)
Parameters
- obj
Type: System.Object
An object to compare with this instance.
Return Value
Type: System.Int32
A 32-bit signed integer that indicates the relative order of the objects being compared. The return value has these meanings:
Value |
Meaning |
|---|---|
Less than zero |
This instance precedes obj in the sort order. |
Zero |
This instance occurs in the same position in the sort order as obj. |
Greater than zero |
This instance follows obj in the sort order. |
Remarks
The CompareTo method is implemented by types whose values can be ordered or sorted. It is called automatically by methods of non-generic collection objects, such as Sort, to order each member of the array. If a custom class or structure does not implement IComparable, its members cannot be ordered and the sort operation can throw an InvalidOperationException.
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 specified in the Return Value section ("precedes", "occurs in the same position as", and "follows") depends on the particular implementation.
By definition, any object compares greater than (or follows) nulla null reference (Nothing in Visual Basic), and two null references compare equal to each other.
The parameter, obj, must be the same type as the class or value type that implements this interface; otherwise, an ArgumentException is thrown.
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 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 code sample illustrates the use of CompareTo to compare a Temperature object implementing IComparable with another object. The Temperature object implements CompareTo by simply wrapping a call to the Int32.CompareTo method.
Imports System.Collections
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
Public Property Fahrenheit() As Double
Get
Return temperatureF
End Get
Set(ByVal Value As Double)
Me.temperatureF = Value
End Set
End Property
Public Property Celsius() As Double
Get
Return (temperatureF - 32) * (5 / 9)
End Get
Set(ByVal Value As Double)
Me.temperatureF = (Value * 9 / 5) + 32
End Set
End Property
End Class
Public Module Example
Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
Dim temperatures(9) As Temperature
' Initialize random number generator.
Dim rnd As New Random()
' Generate 10 temperatures between 0 and 100 randomly.
For ctr As Integer = 1 To 10
Dim degrees As Integer = rnd.Next(0, 100)
Dim temp As New Temperature
temp.Fahrenheit = degrees
temperatures(ctr - 1) = temp
Next
' Sort Array.
Array.Sort(temperatures)
For Each temp As Temperature In temperatures
outputBlock.Text &= temp.Fahrenheit & vbCrLf
Next
End Sub
End Module
' The example displays the following output (individual
' values may vary because they are randomly generated):
' 2
' 7
' 16
' 17
' 31
' 37
' 58
' 66
' 72
' 95
using System;
using System.Collections;
public class Temperature : IComparable
{
// The temperature value
protected double temperatureF;
public int CompareTo(object obj)
{
if (obj == null) return 1;
Temperature otherTemperature = obj as Temperature;
if (otherTemperature != null)
return this.temperatureF.CompareTo(otherTemperature.temperatureF);
else
throw new ArgumentException("Object is not a Temperature");
}
public double Fahrenheit
{
get
{
return this.temperatureF;
}
set
{
this.temperatureF = value;
}
}
public double Celsius
{
get
{
return (this.temperatureF - 32) * (5.0 / 9);
}
set
{
this.temperatureF = (value * 9.0 / 5) + 32;
}
}
}
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
Temperature[] temperatures = new Temperature[10];
// Initialize random number generator.
Random rnd = new Random();
// Generate 10 temperatures between 0 and 100 randomly.
for (int ctr = 1; ctr <= 10; ctr++)
{
int degrees = rnd.Next(0, 100);
Temperature temp = new Temperature();
temp.Fahrenheit = degrees;
temperatures[ctr - 1] = temp;
}
// Sort ArrayList.
Array.Sort(temperatures);
foreach (Temperature temp in temperatures)
outputBlock.Text += temp.Fahrenheit + "\n";
}
}
// The example displays the following output (individual
// values may vary because they are randomly generated):
// 2
// 7
// 16
// 17
// 31
// 37
// 58
// 66
// 72
// 95
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.
Change History
Date |
History |
Reason |
|---|---|---|
Revised the Return Value and Remarks sections. |
Customer feedback. |