ArrayList.IsReadOnly Propiedad
Definición
Importante
Parte de la información hace referencia a la versión preliminar del producto, que puede haberse modificado sustancialmente antes de lanzar la versión definitiva. Microsoft no otorga ninguna garantía, explícita o implícita, con respecto a la información proporcionada aquí.
Obtiene un valor que indica si ArrayList es de solo lectura.
public:
virtual property bool IsReadOnly { bool get(); };
public virtual bool IsReadOnly { get; }
member this.IsReadOnly : bool
Public Overridable ReadOnly Property IsReadOnly As Boolean
Valor de propiedad
Es true
si la interfaz ArrayList es de solo lectura; de lo contrario, es false
. De manera predeterminada, es false
.
Implementaciones
Ejemplos
En el ejemplo de código siguiente se muestra cómo crear un contenedor de solo lectura alrededor de y ArrayList cómo determinar si un ArrayList es de solo lectura.
#using <system.dll>
using namespace System;
using namespace System::Collections;
int main()
{
// Creates and initializes a new ArrayList.
ArrayList^ myAL = gcnew ArrayList;
myAL->Add( "red" );
myAL->Add( "orange" );
myAL->Add( "yellow" );
// Creates a read-only copy of the ArrayList.
ArrayList^ myReadOnlyAL = ArrayList::ReadOnly( myAL );
// Displays whether the ArrayList is read-only or writable.
Console::WriteLine( "myAL is {0}.", myAL->IsReadOnly ? (String^)"read-only" : "writable" );
Console::WriteLine( "myReadOnlyAL is {0}.", myReadOnlyAL->IsReadOnly ? (String^)"read-only" : "writable" );
// Displays the contents of both collections.
Console::WriteLine( "\nInitially," );
Console::WriteLine( "The original ArrayList myAL contains:" );
for ( int i(0); i < myAL->Count; ++i )
Console::WriteLine( " {0}", static_cast<String^>(myAL[ i ]) );
Console::WriteLine( "The read-only ArrayList myReadOnlyAL contains:" );
for ( int i(0); i < myReadOnlyAL->Count; ++i )
Console::WriteLine( " {0}", static_cast<String^>(myReadOnlyAL[ i ]) );
// Adding an element to a read-only ArrayList throws an exception.
Console::WriteLine( "\nTrying to add a new element to the read-only ArrayList:" );
try
{
myReadOnlyAL->Add( "green" );
}
catch ( Exception^ myException )
{
Console::WriteLine( String::Concat( "Exception: ", myException->ToString() ) );
}
// Adding an element to the original ArrayList affects the read-only ArrayList.
myAL->Add( "blue" );
// Displays the contents of both collections again.
Console::WriteLine( "\nAfter adding a new element to the original ArrayList," );
Console::WriteLine( "The original ArrayList myAL contains:" );
for ( int i(0); i < myAL->Count; ++i )
Console::WriteLine( " {0}", static_cast<String^>(myAL[ i ]) );
Console::WriteLine( "The read-only ArrayList myReadOnlyAL contains:" );
for ( int i(0); i < myReadOnlyAL->Count; ++i )
Console::WriteLine( " {0}", static_cast<String^>(myReadOnlyAL[ i ]) );
}
/*
This code produces the following output.
myAL is writable.
myReadOnlyAL is read-only.
Initially,
The original ArrayList myAL contains:
red
orange
yellow
The read-only ArrayList myReadOnlyAL contains:
red
orange
yellow
Trying to add a new element to the read-only ArrayList:
Exception: System.NotSupportedException: Collection is read-only.
at System.Collections.ReadOnlyArrayList.Add(Object obj)
at SamplesArrayList.Main()
After adding a new element to the original ArrayList,
The original ArrayList myAL contains:
red
orange
yellow
blue
The read-only ArrayList myReadOnlyAL contains:
red
orange
yellow
blue
*/
using System;
using System.Collections;
public class SamplesArrayList {
public static void Main() {
// Creates and initializes a new ArrayList.
ArrayList myAL = new ArrayList();
myAL.Add( "red" );
myAL.Add( "orange" );
myAL.Add( "yellow" );
// Creates a read-only copy of the ArrayList.
ArrayList myReadOnlyAL = ArrayList.ReadOnly( myAL );
// Displays whether the ArrayList is read-only or writable.
Console.WriteLine( "myAL is {0}.", myAL.IsReadOnly ? "read-only" : "writable" );
Console.WriteLine( "myReadOnlyAL is {0}.", myReadOnlyAL.IsReadOnly ? "read-only" : "writable" );
// Displays the contents of both collections.
Console.WriteLine( "\nInitially," );
Console.WriteLine( "The original ArrayList myAL contains:" );
foreach ( string myStr in myAL )
Console.WriteLine( " {0}", myStr );
Console.WriteLine( "The read-only ArrayList myReadOnlyAL contains:" );
foreach ( string myStr in myReadOnlyAL )
Console.WriteLine( " {0}", myStr );
// Adding an element to a read-only ArrayList throws an exception.
Console.WriteLine( "\nTrying to add a new element to the read-only ArrayList:" );
try {
myReadOnlyAL.Add("green");
} catch ( Exception myException ) {
Console.WriteLine("Exception: " + myException.ToString());
}
// Adding an element to the original ArrayList affects the read-only ArrayList.
myAL.Add( "blue" );
// Displays the contents of both collections again.
Console.WriteLine( "\nAfter adding a new element to the original ArrayList," );
Console.WriteLine( "The original ArrayList myAL contains:" );
foreach ( string myStr in myAL )
Console.WriteLine( " {0}", myStr );
Console.WriteLine( "The read-only ArrayList myReadOnlyAL contains:" );
foreach ( string myStr in myReadOnlyAL )
Console.WriteLine( " {0}", myStr );
}
}
/*
This code produces the following output.
myAL is writable.
myReadOnlyAL is read-only.
Initially,
The original ArrayList myAL contains:
red
orange
yellow
The read-only ArrayList myReadOnlyAL contains:
red
orange
yellow
Trying to add a new element to the read-only ArrayList:
Exception: System.NotSupportedException: Collection is read-only.
at System.Collections.ReadOnlyArrayList.Add(Object obj)
at SamplesArrayList.Main()
After adding a new element to the original ArrayList,
The original ArrayList myAL contains:
red
orange
yellow
blue
The read-only ArrayList myReadOnlyAL contains:
red
orange
yellow
blue
*/
Imports System.Collections
Public Class SamplesArrayList
Public Shared Sub Main()
Dim myStr As [String]
' Creates and initializes a new ArrayList.
Dim myAL As New ArrayList()
myAL.Add("red")
myAL.Add("orange")
myAL.Add("yellow")
' Creates a read-only copy of the ArrayList.
Dim myReadOnlyAL As ArrayList = ArrayList.ReadOnly(myAL)
' Displays whether the ArrayList is read-only or writable.
If myAL.IsReadOnly Then
Console.WriteLine("myAL is read-only.")
Else
Console.WriteLine("myAL is writable.")
End If
If myReadOnlyAL.IsReadOnly Then
Console.WriteLine("myReadOnlyAL is read-only.")
Else
Console.WriteLine("myReadOnlyAL is writable.")
End If
' Displays the contents of both collections.
Console.WriteLine()
Console.WriteLine("Initially,")
Console.WriteLine("The original ArrayList myAL contains:")
For Each myStr In myAL
Console.WriteLine(" {0}", myStr)
Next myStr
Console.WriteLine("The read-only ArrayList myReadOnlyAL contains:")
For Each myStr In myReadOnlyAL
Console.WriteLine(" {0}", myStr)
Next myStr
' Adding an element to a read-only ArrayList throws an exception.
Console.WriteLine()
Console.WriteLine("Trying to add a new element to the read-only ArrayList:")
Try
myReadOnlyAL.Add("green")
Catch myException As Exception
Console.WriteLine(("Exception: " + myException.ToString()))
End Try
' Adding an element to the original ArrayList affects the read-only ArrayList.
myAL.Add("blue")
' Displays the contents of both collections again.
Console.WriteLine()
Console.WriteLine("After adding a new element to the original ArrayList,")
Console.WriteLine("The original ArrayList myAL contains:")
For Each myStr In myAL
Console.WriteLine(" {0}", myStr)
Next myStr
Console.WriteLine("The read-only ArrayList myReadOnlyAL contains:")
For Each myStr In myReadOnlyAL
Console.WriteLine(" {0}", myStr)
Next myStr
End Sub
End Class
'This code produces the following output.
'
'myAL is writable.
'myReadOnlyAL is read-only.
'
'Initially,
'The original ArrayList myAL contains:
' red
' orange
' yellow
'The read-only ArrayList myReadOnlyAL contains:
' red
' orange
' yellow
'
'Trying to add a new element to the read-only ArrayList:
'Exception: System.NotSupportedException: Collection is read-only.
' at System.Collections.ReadOnlyArrayList.Add(Object obj)
' at SamplesArrayList.Main()
'
'After adding a new element to the original ArrayList,
'The original ArrayList myAL contains:
' red
' orange
' yellow
' blue
'The read-only ArrayList myReadOnlyAL contains:
' red
' orange
' yellow
' blue
Comentarios
Una colección de solo lectura no permite que se agreguen, quiten o modifiquen elementos una vez que se ha creado.
Una colección que es de solo lectura es simplemente una colección con un contenedor que impide modificar la colección; por lo tanto, si se realizan cambios en la colección subyacente, la colección de solo lectura refleja esos cambios.
Recuperar el valor de esta propiedad es una O(1)
operación.
Se aplica a
Consulte también
Comentarios
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