Array.AsReadOnly<T>(T[]) Method
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Returns a read-only wrapper for the specified array.
public:
generic <typename T>
static System::Collections::ObjectModel::ReadOnlyCollection<T> ^ AsReadOnly(cli::array <T> ^ array);
public static System.Collections.ObjectModel.ReadOnlyCollection<T> AsReadOnly<T> (T[] array);
static member AsReadOnly : 'T[] -> System.Collections.ObjectModel.ReadOnlyCollection<'T>
Public Shared Function AsReadOnly(Of T) (array As T()) As ReadOnlyCollection(Of T)
- T
The type of the elements of the array.
- array
- T[]
The one-dimensional, zero-based array to wrap in a read-only ReadOnlyCollection<T> wrapper.
A read-only ReadOnlyCollection<T> wrapper for the specified array.
array
is null
.
The following example wraps an array in a read-only ReadOnlyCollection<T>.
using namespace System;
using namespace System::Collections::Generic;
namespace Samples
{
public ref class SamplesArray
{
public:
static void Work()
{
// Create and initialize a new string array.
array <String^>^ textArray =
{"The", "quick", "brown", "fox"};
// Display the values of the array.
Console::WriteLine("The string array initially contains "
"the following values:");
PrintIndexAndValues(textArray);
// Create a read-only IList wrapper around the array.
IList <String^>^ textList = Array::AsReadOnly(textArray);
// Display the values of the read-only IList.
Console::WriteLine("The read-only IList contains "
"the following values:");
PrintIndexAndValues(textList);
// Attempt to change a value through the wrapper.
try
{
textList[3] = "CAT";
}
catch (NotSupportedException^ ex)
{
Console::WriteLine("{0} - {1}", ex->GetType(),
ex->Message);
Console::WriteLine();
}
// Change a value in the original array.
textArray[2] = "RED";
// Display the values of the array.
Console::WriteLine("After changing the third element,"
"the string array contains the following values:");
PrintIndexAndValues(textArray);
// Display the values of the read-only IList.
Console::WriteLine("After changing the third element, the"
" read-only IList contains the following values:");
PrintIndexAndValues(textList);
}
static void PrintIndexAndValues(array<String^>^ textArray)
{
for (int i = 0; i < textArray->Length; i++)
{
Console::WriteLine(" [{0}] : {1}", i, textArray[i]);
}
Console::WriteLine();
}
static void PrintIndexAndValues(IList<String^>^ textList)
{
for (int i = 0; i < textList->Count; i++)
{
Console::WriteLine(" [{0}] : {1}", i, textList[i]);
}
Console::WriteLine();
}
};
}
int main()
{
Samples::SamplesArray::Work();
}
/*
This code produces the following output.
The string array initially contains the following values:
[0] : The
[1] : quick
[2] : brown
[3] : fox
The read-only IList contains the following values:
[0] : The
[1] : quick
[2] : brown
[3] : fox
System.NotSupportedException - Collection is read-only.
After changing the third element, the string array contains the following values:
[0] : The
[1] : quick
[2] : RED
[3] : fox
After changing the third element, the read-only IList contains the following values:
[0] : The
[1] : quick
[2] : RED
[3] : fox
*/
using System;
using System.Collections.Generic;
public class SamplesArray {
public static void Main() {
// Create and initialize a new string array.
String[] myArr = { "The", "quick", "brown", "fox" };
// Display the values of the array.
Console.WriteLine( "The string array initially contains the following values:" );
PrintIndexAndValues( myArr );
// Create a read-only IList wrapper around the array.
IList<string> myList = Array.AsReadOnly( myArr );
// Display the values of the read-only IList.
Console.WriteLine( "The read-only IList contains the following values:" );
PrintIndexAndValues( myList );
// Attempt to change a value through the wrapper.
try {
myList[3] = "CAT";
}
catch ( NotSupportedException e ) {
Console.WriteLine( "{0} - {1}", e.GetType(), e.Message );
Console.WriteLine();
}
// Change a value in the original array.
myArr[2] = "RED";
// Display the values of the array.
Console.WriteLine( "After changing the third element, the string array contains the following values:" );
PrintIndexAndValues( myArr );
// Display the values of the read-only IList.
Console.WriteLine( "After changing the third element, the read-only IList contains the following values:" );
PrintIndexAndValues( myList );
}
public static void PrintIndexAndValues( String[] myArr ) {
for ( int i = 0; i < myArr.Length; i++ ) {
Console.WriteLine( " [{0}] : {1}", i, myArr[i] );
}
Console.WriteLine();
}
public static void PrintIndexAndValues( IList<string> myList ) {
for ( int i = 0; i < myList.Count; i++ ) {
Console.WriteLine( " [{0}] : {1}", i, myList[i] );
}
Console.WriteLine();
}
}
/*
This code produces the following output.
The string array initially contains the following values:
[0] : The
[1] : quick
[2] : brown
[3] : fox
The read-only IList contains the following values:
[0] : The
[1] : quick
[2] : brown
[3] : fox
System.NotSupportedException - Collection is read-only.
After changing the third element, the string array contains the following values:
[0] : The
[1] : quick
[2] : RED
[3] : fox
After changing the third element, the read-only IList contains the following values:
[0] : The
[1] : quick
[2] : RED
[3] : fox
*/
open System
open System.Collections.Generic
let printIndexAndValues (myList: IList<'a>) =
for i = 0 to myList.Count - 1 do
printfn $" [{i}] : {myList[i]}"
printfn ""
// Create and initialize a new string array.
let myArr = [| "The"; "quick"; "brown"; "fox" |]
// Display the values of the array.
printfn "The string array initially contains the following values:"
printIndexAndValues myArr
// Create a read-only IList wrapper around the array.
let myList: IList<_> = Array.AsReadOnly myArr
// Display the values of the read-only IList.
printfn "The read-only IList contains the following values:"
printIndexAndValues myList
// Attempt to change a value through the wrapper.
try
myList[3] <- "CAT"
with :? NotSupportedException as e ->
printfn $"{e.GetType()} - {e.Message}\n"
// Change a value in the original array.
myArr[2] <- "RED"
// Display the values of the array.
printfn "After changing the third element, the string array contains the following values:"
printIndexAndValues myArr
// Display the values of the read-only IList.
printfn "After changing the third element, the read-only IList contains the following values:"
printIndexAndValues myList
// This code produces the following output.
// The string array initially contains the following values:
// [0] : The
// [1] : quick
// [2] : brown
// [3] : fox
//
// The read-only IList contains the following values:
// [0] : The
// [1] : quick
// [2] : brown
// [3] : fox
//
// System.NotSupportedException - Collection is read-only.
//
// After changing the third element, the string array contains the following values:
// [0] : The
// [1] : quick
// [2] : RED
// [3] : fox
//
// After changing the third element, the read-only IList contains the following values:
// [0] : The
// [1] : quick
// [2] : RED
// [3] : fox
Imports System.Collections.Generic
Public Class SamplesArray
Public Shared Sub Main()
' Create and initialize a new string array.
Dim myArr As String() = {"The", "quick", "brown", "fox"}
' Display the values of the array.
Console.WriteLine("The string array initially contains the following values:")
PrintIndexAndValues(myArr)
' Create a read-only IList wrapper around the array.
Dim myList As IList(Of String) = Array.AsReadOnly(myArr) '
' Display the values of the read-only IList.
Console.WriteLine("The read-only IList contains the following values:")
PrintIndexAndValues(myList)
' Attempt to change a value through the wrapper.
Try
myList(3) = "CAT"
Catch e As NotSupportedException
Console.WriteLine("{0} - {1}", e.GetType(), e.Message)
Console.WriteLine()
End Try
' Change a value in the original array.
myArr(2) = "RED"
' Display the values of the array.
Console.WriteLine("After changing the third element, the string array contains the following values:")
PrintIndexAndValues(myArr)
' Display the values of the read-only IList.
Console.WriteLine("After changing the third element, the read-only IList contains the following values:")
PrintIndexAndValues(myList)
End Sub
Overloads Public Shared Sub PrintIndexAndValues(myArr() As String)
Dim i As Integer
For i = 0 To myArr.Length - 1
Console.WriteLine(" [{0}] : {1}", i, myArr(i))
Next i
Console.WriteLine()
End Sub
Overloads Public Shared Sub PrintIndexAndValues(myList As IList(Of String))
Dim i As Integer
For i = 0 To myList.Count - 1
Console.WriteLine(" [{0}] : {1}", i, myList(i))
Next i
Console.WriteLine()
End Sub
End Class
'This code produces the following output.
'
'The string array initially contains the following values:
' [0] : The
' [1] : quick
' [2] : brown
' [3] : fox
'
'The read-only IList contains the following values:
' [0] : The
' [1] : quick
' [2] : brown
' [3] : fox
'
'System.NotSupportedException - Collection is read-only.
'
'After changing the third element, the string array contains the following values:
' [0] : The
' [1] : quick
' [2] : RED
' [3] : fox
'
'After changing the third element, the read-only IList contains the following values:
' [0] : The
' [1] : quick
' [2] : RED
' [3] : fox
To prevent any modifications to the array, expose the array only through this wrapper.
A collection that is read-only is simply a collection with a wrapper that prevents modifying the collection; therefore, if changes are made to the underlying collection, the read-only collection reflects those changes.
This method is an O(1) operation.
Produit | Versions |
---|---|
.NET | Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 2.0, 2.1 |
Commentaires sur .NET
.NET est un projet open source. Sélectionnez un lien pour fournir des commentaires :