IEnumerable<T>.GetEnumerator Metoda
Definice
Získá enumerátor, který provádí iteraci v kolekci.Returns an enumerator that iterates through the collection.
public:
System::Collections::Generic::IEnumerator<T> ^ GetEnumerator();public System.Collections.Generic.IEnumerator<out T> GetEnumerator ();public System.Collections.Generic.IEnumerator<T> GetEnumerator ();abstract member GetEnumerator : unit -> System.Collections.Generic.IEnumerator<'T>Public Function GetEnumerator () As IEnumerator(Of Out T)Public Function GetEnumerator () As IEnumerator(Of T)Návraty
Enumerátor, který lze použít k iteraci kolekce.An enumerator that can be used to iterate through the collection.
Příklady
Následující příklad ukazuje, jak implementovat IEnumerable<T> rozhraní a používá tuto implementaci k vytvoření dotazu LINQ.The following example demonstrates how to implement the IEnumerable<T> interface and uses that implementation to create a LINQ query. Při implementaci nástroje je IEnumerable<T> nutné implementovat také IEnumerator<T> nebo, pouze pro C#, lze použít klíčové slovo yield .When you implement IEnumerable<T>, you must also implement IEnumerator<T> or, for C# only, you can use the yield keyword. Implementace IEnumerator<T> také vyžaduje IDisposable implementaci, která se zobrazí v tomto příkladu.Implementing IEnumerator<T> also requires IDisposable to be implemented, which you will see in this example.
using System;
using System.IO;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
public class App
{
// Excercise the Iterator and show that it's more
// performant.
public static void Main()
{
TestStreamReaderEnumerable();
Console.WriteLine("---");
TestReadingFile();
}
public static void TestStreamReaderEnumerable()
{
// Check the memory before the iterator is used.
long memoryBefore = GC.GetTotalMemory(true);
IEnumerable<String> stringsFound;
// Open a file with the StreamReaderEnumerable and check for a string.
try {
stringsFound =
from line in new StreamReaderEnumerable(@"c:\temp\tempFile.txt")
where line.Contains("string to search for")
select line;
Console.WriteLine("Found: " + stringsFound.Count());
}
catch (FileNotFoundException) {
Console.WriteLine(@"This example requires a file named C:\temp\tempFile.txt.");
return;
}
// Check the memory after the iterator and output it to the console.
long memoryAfter = GC.GetTotalMemory(false);
Console.WriteLine("Memory Used With Iterator = \t"
+ string.Format(((memoryAfter - memoryBefore) / 1000).ToString(), "n") + "kb");
}
public static void TestReadingFile()
{
long memoryBefore = GC.GetTotalMemory(true);
StreamReader sr;
try {
sr = File.OpenText("c:\\temp\\tempFile.txt");
}
catch (FileNotFoundException) {
Console.WriteLine(@"This example requires a file named C:\temp\tempFile.txt.");
return;
}
// Add the file contents to a generic list of strings.
List<string> fileContents = new List<string>();
while (!sr.EndOfStream) {
fileContents.Add(sr.ReadLine());
}
// Check for the string.
var stringsFound =
from line in fileContents
where line.Contains("string to search for")
select line;
sr.Close();
Console.WriteLine("Found: " + stringsFound.Count());
// Check the memory after when the iterator is not used, and output it to the console.
long memoryAfter = GC.GetTotalMemory(false);
Console.WriteLine("Memory Used Without Iterator = \t" +
string.Format(((memoryAfter - memoryBefore) / 1000).ToString(), "n") + "kb");
}
}
// A custom class that implements IEnumerable(T). When you implement IEnumerable(T),
// you must also implement IEnumerable and IEnumerator(T).
public class StreamReaderEnumerable : IEnumerable<string>
{
private string _filePath;
public StreamReaderEnumerable(string filePath)
{
_filePath = filePath;
}
// Must implement GetEnumerator, which returns a new StreamReaderEnumerator.
public IEnumerator<string> GetEnumerator()
{
return new StreamReaderEnumerator(_filePath);
}
// Must also implement IEnumerable.GetEnumerator, but implement as a private method.
private IEnumerator GetEnumerator1()
{
return this.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator1();
}
}
// When you implement IEnumerable(T), you must also implement IEnumerator(T),
// which will walk through the contents of the file one line at a time.
// Implementing IEnumerator(T) requires that you implement IEnumerator and IDisposable.
public class StreamReaderEnumerator : IEnumerator<string>
{
private StreamReader _sr;
public StreamReaderEnumerator(string filePath)
{
_sr = new StreamReader(filePath);
}
private string _current;
// Implement the IEnumerator(T).Current publicly, but implement
// IEnumerator.Current, which is also required, privately.
public string Current
{
get
{
if (_sr == null || _current == null)
{
throw new InvalidOperationException();
}
return _current;
}
}
private object Current1
{
get { return this.Current; }
}
object IEnumerator.Current
{
get { return Current1; }
}
// Implement MoveNext and Reset, which are required by IEnumerator.
public bool MoveNext()
{
_current = _sr.ReadLine();
if (_current == null)
return false;
return true;
}
public void Reset()
{
_sr.DiscardBufferedData();
_sr.BaseStream.Seek(0, SeekOrigin.Begin);
_current = null;
}
// Implement IDisposable, which is also implemented by IEnumerator(T).
private bool disposedValue = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!this.disposedValue)
{
if (disposing)
{
// Dispose of managed resources.
}
_current = null;
if (_sr != null) {
_sr.Close();
_sr.Dispose();
}
}
this.disposedValue = true;
}
~StreamReaderEnumerator()
{
Dispose(false);
}
}
// This example displays output similar to the following:
// Found: 2
// Memory Used With Iterator = 33kb
// ---
// Found: 2
// Memory Used Without Iterator = 206kb
Imports System.IO
Imports System.Collections
Imports System.Collections.Generic
Imports System.Linq
Public Module App
' Excercise the Iterator and show that it's more performant.
Public Sub Main()
TestStreamReaderEnumerable()
Console.WriteLine("---")
TestReadingFile()
End Sub
Public Sub TestStreamReaderEnumerable()
' Check the memory before the iterator is used.
Dim memoryBefore As Long = GC.GetTotalMemory(true)
Dim stringsFound As IEnumerable(Of String)
' Open a file with the StreamReaderEnumerable and check for a string.
Try
stringsFound =
from line in new StreamReaderEnumerable("c:\temp\tempFile.txt")
where line.Contains("string to search for")
select line
Console.WriteLine("Found: {0}", stringsFound.Count())
Catch e As FileNotFoundException
Console.WriteLine("This example requires a file named C:\temp\tempFile.txt.")
Return
End Try
' Check the memory after the iterator and output it to the console.
Dim memoryAfter As Long = GC.GetTotalMemory(false)
Console.WriteLine("Memory Used with Iterator = {1}{0} kb",
(memoryAfter - memoryBefore)\1000, vbTab)
End Sub
Public Sub TestReadingFile()
Dim memoryBefore As Long = GC.GetTotalMemory(true)
Dim sr As StreamReader
Try
sr = File.OpenText("c:\temp\tempFile.txt")
Catch e As FileNotFoundException
Console.WriteLine("This example requires a file named C:\temp\tempFile.txt.")
Return
End Try
' Add the file contents to a generic list of strings.
Dim fileContents As New List(Of String)()
Do While Not sr.EndOfStream
fileContents.Add(sr.ReadLine())
Loop
' Check for the string.
Dim stringsFound =
from line in fileContents
where line.Contains("string to search for")
select line
sr.Close()
Console.WriteLine("Found: {0}", stringsFound.Count())
' Check the memory after when the iterator is not used, and output it to the console.
Dim memoryAfter As Long = GC.GetTotalMemory(False)
Console.WriteLine("Memory Used without Iterator = {1}{0} kb",
(memoryAfter - memoryBefore)\1000, vbTab)
End Sub
End Module
' A custom class that implements IEnumerable(T). When you implement IEnumerable(T),
' you must also implement IEnumerable and IEnumerator(T).
Public Class StreamReaderEnumerable : Implements IEnumerable(Of String)
Private _filePath As String
Public Sub New(filePath As String)
_filePath = filePath
End Sub
' Must implement GetEnumerator, which returns a new StreamReaderEnumerator.
Public Function GetEnumerator() As IEnumerator(Of String) _
Implements IEnumerable(Of String).GetEnumerator
Return New StreamReaderEnumerator(_filePath)
End Function
' Must also implement IEnumerable.GetEnumerator, but implement as a private method.
Private Function GetEnumerator1() As IEnumerator _
Implements IEnumerable.GetEnumerator
Return Me.GetEnumerator()
End Function
End Class
' When you implement IEnumerable(T), you must also implement IEnumerator(T),
' which will walk through the contents of the file one line at a time.
' Implementing IEnumerator(T) requires that you implement IEnumerator and IDisposable.
Public Class StreamReaderEnumerator : Implements IEnumerator(Of String)
Private _sr As StreamReader
Public Sub New(filePath As String)
_sr = New StreamReader(filePath)
End Sub
Private _current As String
' Implement the IEnumerator(T).Current Publicly, but implement
' IEnumerator.Current, which is also required, privately.
Public ReadOnly Property Current As String _
Implements IEnumerator(Of String).Current
Get
If _sr Is Nothing OrElse _current Is Nothing
Throw New InvalidOperationException()
End If
Return _current
End Get
End Property
Private ReadOnly Property Current1 As Object _
Implements IEnumerator.Current
Get
Return Me.Current
End Get
End Property
' Implement MoveNext and Reset, which are required by IEnumerator.
Public Function MoveNext() As Boolean _
Implements IEnumerator.MoveNext
_current = _sr.ReadLine()
if _current Is Nothing Then Return False
Return True
End Function
Public Sub Reset() _
Implements IEnumerator.Reset
_sr.DiscardBufferedData()
_sr.BaseStream.Seek(0, SeekOrigin.Begin)
_current = Nothing
End Sub
' Implement IDisposable, which is also implemented by IEnumerator(T).
Private disposedValue As Boolean = False
Public Sub Dispose() _
Implements IDisposable.Dispose
Dispose(True)
GC.SuppressFinalize(Me)
End Sub
Protected Overridable Sub Dispose(disposing As Boolean)
If Not Me.disposedValue Then
If disposing Then
' Dispose of managed resources.
End If
_current = Nothing
If _sr IsNot Nothing Then
_sr.Close()
_sr.Dispose()
End If
End If
Me.disposedValue = True
End Sub
Protected Overrides Sub Finalize()
Dispose(False)
End Sub
End Class
' This example displays output similar to the following:
' Found: 2
' Memory Used With Iterator = 33kb
' ---
' Found: 2
' Memory Used Without Iterator = 206kb
Pro jiný příklad jazyka C#, který ukazuje, jak implementovat IEnumerable<T> rozhraní, naleznete v tématu Obecné příklady.For another C# example that demonstrates how to implement the IEnumerable<T> interface, see the Generics Sample. Tato ukázka používá yield klíčové slovo namísto implementace IEnumerator<T> .This sample uses of the yield keyword instead of implementing IEnumerator<T>.
Poznámky
Vráceno IEnumerator<T> poskytuje možnost iterace v kolekci vyvoláním Current Vlastnosti. Enumerátory lze použít ke čtení dat v kolekci, ale nikoli ke změně kolekce.The returned IEnumerator<T> provides the ability to iterate through the collection by exposing a Current property .You can use enumerators to read the data in a collection, but not to modify the collection.
Zpočátku je enumerátor umístěn před první prvek v kolekci.Initially, the enumerator is positioned before the first element in the collection. Na této pozici Current není definován.At this position, Current is undefined. Proto je nutné zavolat MoveNext metodu pro posunutí čítače na první prvek kolekce před čtením hodnoty Current .Therefore, you must call the MoveNext method to advance the enumerator to the first element of the collection before reading the value of Current.
Current vrátí stejný objekt, dokud MoveNext je znovu volán jako MoveNext nastavení Current dalšího prvku.Current returns the same object until MoveNext is called again as MoveNext sets Current to the next element.
Pokud MoveNext předá konec kolekce, enumerátor je umístěn za posledním prvkem v kolekci a MoveNext vrátí false .If MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. Když je na této pozici enumerátor, následné volání MoveNext vrátí také false .When the enumerator is at this position, subsequent calls to MoveNext also return false. Pokud poslední volání MoveNext vráceno false Current není definováno.If the last call to MoveNext returned false, Current is undefined. Nemůžete nastavit Current na první prvek kolekce znovu. místo toho je nutné vytvořit novou instanci enumerátoru.You cannot set Current to the first element of the collection again; you must create a new enumerator instance instead.
Pokud jsou provedeny změny v kolekci, jako je například přidání, úprava nebo odstranění prvků, chování čítače není definováno.If changes are made to the collection, such as adding, modifying, or deleting elements, the behavior of the enumerator is undefined.
Enumerátor nemá výhradní přístup ke kolekci, takže enumerátor zůstane platný, dokud kolekce nezůstane beze změny.An enumerator does not have exclusive access to the collection so an enumerator remains valid as long as the collection remains unchanged. Pokud jsou v kolekci provedeny změny, jako je například přidání, úprava nebo odstranění prvků, enumerátor je neověřen a může se zobrazit neočekávané výsledky.If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is invalidated and you may get unexpected results. Výčet kolekce není také bezpečný pro přístup z více vláken.Also, enumerating a collection is not a thread-safe procedure. Aby bylo zajištěno zabezpečení více vlákny, měli byste uzamknout shromažďování během enumerátoru nebo provést synchronizaci v kolekci.To guarantee thread-safety, you should lock the collection during enumerator or implement synchronization on the collection.
Výchozí implementace kolekcí v System.Collections.Generic oboru názvů se nesynchronizují.Default implementations of collections in the System.Collections.Generic namespace aren't synchronized.