Nullable<T>.GetValueOrDefault Метод

Определение

Пространство имен:

System

Сборка:

System.Runtime.dll

Извлекает значение текущего объекта Nullable<T> или значение по умолчанию.

Перегрузки

GetValueOrDefault()	Извлекает значение текущего объекта Nullable<T> или значение базового типа этого объекта по умолчанию.
GetValueOrDefault(T)	Извлекает значение текущего объекта Nullable<T> или заданное значение по умолчанию.

Примеры

В следующем примере кода извлекается значение Nullable<T> объекта , если оно определено; в противном случае возвращается значение по умолчанию или определенное значение по умолчанию.

// This code example demonstrates the
// Nullable<T>.GetValueOrDefault methods.

using System;

class Sample
{
    public static void Main()
    {
    float? mySingle = 12.34f;
    float? yourSingle = -1.0f;

   Console.WriteLine("*** Display a value or the default value ***\n");
// Display the values of mySingle and yourSingle.

    Display("A1", mySingle, yourSingle);

// Assign the value of mySingle to yourSingle, then display the values
// of mySingle and yourSingle. The yourSingle variable is assigned the
// value 12.34 because mySingle has a value.

    yourSingle = mySingle.GetValueOrDefault();
    Display("A2", mySingle, yourSingle);

// Assign null (Nothing in Visual Basic) to mySingle, which means no value is
// defined for mySingle. Then assign the value of mySingle to yourSingle and
// display the values of both variables. The default value of all binary zeroes
// is assigned to yourSingle because mySingle has no value.

    mySingle = null;
    yourSingle = mySingle.GetValueOrDefault();
    Display("A3", mySingle, yourSingle);

// Reassign the original values of mySingle and yourSingle.
    mySingle = 12.34f;
    yourSingle = -1.0f;

    Console.Write("\n*** Display a value or the ");
    Console.WriteLine("specified default value ***\n");

// Display the values of mySingle and yourSingle.
    Display("B1", mySingle, yourSingle);

// Assign the value of mySingle to yourSingle, then display the values
// of mySingle and yourSingle. The yourSingle variable is assigned the
// value 12.34 because mySingle has a value.

    yourSingle = mySingle.GetValueOrDefault(-222.22f);
    Display("B2", mySingle, yourSingle);

// Assign null (Nothing in Visual Basic) to mySingle, which means no value is
// defined for mySingle. Then assign the value of mySingle to yourSingle and
// display the values of both variables. The specified default value of -333.33
// is assigned to yourSingle because mySingle has no value.

    mySingle = null;
    yourSingle = mySingle.GetValueOrDefault(-333.33f);
    Display("B3", mySingle, yourSingle);
    }

// Display the values of two nullable of System.Single structures.
// The Console.WriteLine method automatically calls the ToString methods of
// each input argument to display its values. If no value is defined for a
// nullable type, the ToString method for that argument returns the empty
// string ("").
    public static void Display(string title, float? dspMySingle, float? dspYourSingle)
    {
    Console.WriteLine("{0}) mySingle = [{1}], yourSingle = [{2}]",
                      title, dspMySingle, dspYourSingle);
    }
}

/*
This code example produces the following results:

A1) mySingle = [12.34], yourSingle = [-1]
A2) mySingle = [12.34], yourSingle = [12.34]
A3) mySingle = [], yourSingle = [0]

*** Display a value or the specified default value ***

B1) mySingle = [12.34], yourSingle = [-1]
B2) mySingle = [12.34], yourSingle = [12.34]
B3) mySingle = [], yourSingle = [-333.33]

*/

// This code example demonstrates the
// Nullable<T>.GetValueOrDefault methods.
open System

// Display the values of two nullable of System.Single structures.
// The printfn string interpolation automatically calls the ToString methods of
// each input argument to display its values. If no value is defined for a
// nullable type, the ToString method for that argument returns the empty
// string ("").
let display title dspMySingle dspYourSingle =
    printfn $"{title}) mySingle = [{dspMySingle}], yourSingle = [{dspYourSingle}]"

let mySingle = Nullable 12.34f
let yourSingle = Nullable -1f

[<EntryPoint>]
let main _ =
    printfn "*** Display a value or the default value ***\n"
    // Display the values of mySingle and yourSingle.

    display "A1" mySingle yourSingle

    // Shadow the value of mySingle to yourSingle, then display the values
    // of mySingle and yourSingle. The yourSingle variable is assigned the
    // value 12.34 because mySingle has a value.

    let yourSingle = mySingle.GetValueOrDefault()
    display "A2" mySingle yourSingle

    // Shadow null (Nothing in Visual Basic) to mySingle, which means no value is
    // defined for mySingle. Then assign the value of mySingle to yourSingle and
    // display the values of both variables. The default value of all binary zeroes
    // is assigned to yourSingle because mySingle has no value.

    let mySingle = Nullable()
    let yourSingle = mySingle.GetValueOrDefault()
    display "A3" mySingle yourSingle

    // Shadow the original values of mySingle and yourSingle.
    let mySingle = Nullable 12.34f
    let yourSingle = Nullable -1.0f

    printf "\n*** Display a value or the "
    printfn "specified default value ***\n"

    // Display the values of mySingle and yourSingle.
    display "B1" mySingle yourSingle

    // Shadow the value of mySingle to yourSingle, then display the values
    // of mySingle and yourSingle. The yourSingle variable is assigned the
    // value 12.34 because mySingle has a value.

    let yourSingle = mySingle.GetValueOrDefault -222.22f
    display "B2" mySingle yourSingle

    // Shadow null (Nothing in Visual Basic) to mySingle, which means no value is
    // defined for mySingle. Then shadow the value of mySingle to yourSingle and
    // display the values of both variables. The specified default value of -333.33
    // is assigned to yourSingle because mySingle has no value.

    let mySingle = Nullable()
    let yourSingle = mySingle.GetValueOrDefault -333.33f
    display "B3" mySingle yourSingle
    0

// This code example produces the following results:
//     A1) mySingle = [12.34], yourSingle = [-1]
//     A2) mySingle = [12.34], yourSingle = [12.34]
//     A3) mySingle = [], yourSingle = [0]
//     
//     *** Display a value or the specified default value ***
//     
//     B1) mySingle = [12.34], yourSingle = [-1]
//     B2) mySingle = [12.34], yourSingle = [12.34]
//     B3) mySingle = [], yourSingle = [-333.33]

' This code example demonstrates the 
' Nullable(Of T).GetValueOrDefault methods.

Class Sample
    Public Shared Sub Main() 
        Dim mySingle As Nullable(Of System.Single) = 12.34F 
        Dim yourSingle As Nullable(Of System.Single) = - 1.0F 
        
        Console.WriteLine("*** Display a value or the default value ***" & vbCrLf)
    ' Display the values of mySingle and yourSingle.
        Display("A1", mySingle, yourSingle)
        
    ' Assign the value of mySingle to yourSingle, then display the values 
    ' of mySingle and yourSingle. The yourSingle variable is assigned the 
    ' value 12.34 because mySingle has a value.
        yourSingle = mySingle.GetValueOrDefault()
        Display("A2", mySingle, yourSingle)
        
    ' Assign null (Nothing in Visual Basic) to mySingle, which means no value is
    ' defined for mySingle. Then assign the value of mySingle to yourSingle and
    ' display the values of both variables. The default value of all binary zeroes 
    ' is assigned to yourSingle because mySingle has no value.
        mySingle = Nothing
        yourSingle = mySingle.GetValueOrDefault()
        Display("A3", mySingle, yourSingle)
        
    ' Reassign the original values of mySingle and yourSingle.
        mySingle = 12.34F
        yourSingle = - 1.0F
        
        Console.Write(vbCrLf & "*** Display a value or the ")
        Console.WriteLine("specified default value ***" & vbCrLf)
        
    ' Display the values of mySingle and yourSingle.
        Display("B1", mySingle, yourSingle)
        
    ' Assign the value of mySingle to yourSingle, then display the values 
    ' of mySingle and yourSingle. The yourSingle variable is assigned the 
    ' value 12.34 because mySingle has a value.
        yourSingle = mySingle.GetValueOrDefault(- 222.22F)
        Display("B2", mySingle, yourSingle)
        
    ' Assign null (Nothing in Visual Basic) to mySingle, which means no value is
    ' defined for mySingle. Then assign the value of mySingle to yourSingle and
    ' display the values of both variables. The specified default value of -333.33
    ' is assigned to yourSingle because mySingle has no value.
        mySingle = Nothing
        yourSingle = mySingle.GetValueOrDefault(- 333.33F)
        Display("B3", mySingle, yourSingle)
    
    End Sub
     
    
    ' Display the values of two nullable of System.Single structures.
    ' The Console.WriteLine method automatically calls the ToString methods of 
    ' each input argument to display its values. If no value is defined for a
    ' nullable type, the ToString method for that argument returns the empty
    ' string ("").

    Public Shared Sub Display(ByVal title As String, _
                              ByVal dspMySingle As Nullable(Of System.Single), _
                              ByVal dspYourSingle As Nullable(Of System.Single))
        If (True) Then
            Console.WriteLine("{0}) mySingle = [{1}], yourSingle = [{2}]", _
                               title, dspMySingle, dspYourSingle)
        End If
    End Sub
End Class

'
'This code example produces the following results:
'
'A1) mySingle = [12.34], yourSingle = [-1]
'A2) mySingle = [12.34], yourSingle = [12.34]
'A3) mySingle = [], yourSingle = [0]
'
'*** Display a value or the specified default value ***
'
'B1) mySingle = [12.34], yourSingle = [-1]
'B2) mySingle = [12.34], yourSingle = [12.34]
'B3) mySingle = [], yourSingle = [-333.33]
'

GetValueOrDefault()

Исходный код:

Nullable.cs

Извлекает значение текущего объекта Nullable<T> или значение базового типа этого объекта по умолчанию.

public:
 T GetValueOrDefault();

public readonly T GetValueOrDefault ();

member this.GetValueOrDefault : unit -> 'T

Public Function GetValueOrDefault () As T

Возвращаемое значение

T

Значение свойства , Value если HasValue свойство имеет значение true; в противном случае — значение по умолчанию базового типа.

Комментарии

Метод GetValueOrDefault возвращает значение, даже если HasValue свойство имеет значение false (в Value отличие от свойства, которое вызывает исключение). HasValue Если свойство имеет значение false, метод возвращает значение по умолчанию базового типа.

См. также раздел

• GetValueOrDefault(T)

GetValueOrDefault(T)

Исходный код:

Nullable.cs

Извлекает значение текущего объекта Nullable<T> или заданное значение по умолчанию.

public:
 T GetValueOrDefault(T defaultValue);

public readonly T GetValueOrDefault (T defaultValue);

member this.GetValueOrDefault : 'T -> 'T

Public Function GetValueOrDefault (defaultValue As T) As T

Параметры

defaultValue

T

Значение, которое следует вернуть, если свойство HasValue имеет значение false.

Возвращаемое значение

T

Значение свойства Value, если свойство HasValue имеет значение true; в противном случае значение параметра defaultValue.

Комментарии

Метод GetValueOrDefault возвращает значение, даже если HasValue свойство имеет значение false (в Value отличие от свойства, которое вызывает исключение).

См. также раздел

• GetValueOrDefault()