Nullable<T>.GetValueOrDefault Metodo

Definizione

Recupera il valore dell'oggetto Nullable<T> corrente o un valore predefinito.

 GetValueOrDefault() Recupera il valore dell'oggetto Nullable corrente o il valore predefinito del tipo sottostante. GetValueOrDefault(T) Recupera il valore dell'oggetto Nullable corrente o il valore predefinito specificato.

Esempio

Nell'esempio di codice seguente viene recuperato il valore di un Nullable<T> oggetto se tale valore è definito. In caso contrario, recupera il valore predefinito o un valore predefinito specifico.

``````// 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()

Source:
Nullable.cs
Source:
Nullable.cs
Source:
Nullable.cs

Recupera il valore dell'oggetto Nullable<T> corrente o il valore predefinito del tipo sottostante.

``````public:
T GetValueOrDefault();``````
``public T GetValueOrDefault ();``
``public readonly T GetValueOrDefault ();``
``member this.GetValueOrDefault : unit -> 'T``
``Public Function GetValueOrDefault () As T``

Restituisce

T

Valore della Value proprietà se la HasValue proprietà è `true`; in caso contrario, il valore predefinito del tipo sottostante.

Commenti

Il GetValueOrDefault metodo restituisce un valore anche se la proprietà è `false` (a differenza della HasValueValue proprietà, che genera un'eccezione). Se la HasValue proprietà è `false`, il metodo restituisce il valore predefinito del tipo sottostante.

GetValueOrDefault(T)

Source:
Nullable.cs
Source:
Nullable.cs
Source:
Nullable.cs

Recupera il valore dell'oggetto Nullable<T> corrente o il valore predefinito specificato.

``````public:
T GetValueOrDefault(T defaultValue);``````
``public T GetValueOrDefault (T defaultValue);``
``public readonly T GetValueOrDefault (T defaultValue);``
``member this.GetValueOrDefault : 'T -> 'T``
``Public Function GetValueOrDefault (defaultValue As T) As T``

Parametri

defaultValue
T

Valore da restituire se la proprietà HasValue è `false`.

Restituisce

T

Valore della proprietà Value se la proprietà HasValue è `true`; in caso contrario, parametro `defaultValue`.

Commenti

Il GetValueOrDefault metodo restituisce un valore anche se la proprietà è `false` (a differenza della HasValueValue proprietà, che genera un'eccezione).