July 28, 2014
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.
Assembly: mscorlib (in mscorlib.dll)
- Type: System.Object
An object to compare with this instance.
Return ValueType: System.Int32
A 32-bit signed integer that indicates the relative order of the objects being compared. The return value has these meanings:
Less than zero
This instance precedes obj in the sort order.
This instance occurs in the same position in the sort order as obj.
Greater than zero
This instance follows obj in the sort order.
The 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) Nothing, 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 method to determine the ordering of instances of a class.
The following code sample illustrates the use of to compare a Temperature object implementing IComparable with another object. The Temperature object implements 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