# List<T>.Exists(Predicate<T>)List<T>.Exists(Predicate<T>)List<T>.Exists(Predicate<T>)List<T>.Exists(Predicate<T>) Method

## 定義

List<T> に、指定された述語によって定義された条件と一致する要素が含まれているかどうかを判断します。Determines whether the List<T> contains elements that match the conditions defined by the specified predicate.

``````public:
bool Exists(Predicate<T> ^ match);``````
``public bool Exists (Predicate<T> match);``
``member this.Exists : Predicate<'T> -> bool``
``Public Function Exists (match As Predicate(Of T)) As Boolean``

#### パラメーター

match
Predicate<T> Predicate<T> Predicate<T> Predicate<T>

#### 例外

`match``null`です。`match` is `null`.

## 例

``````using System;
using System.Collections.Generic;
// Simple business object. A PartId is used to identify a part
// but the part name can change.
public class Part : IEquatable<Part>
{
public string PartName { get; set; }
public int PartId { get; set; }

public override string ToString()
{
return "ID: " + PartId + "   Name: " + PartName;
}
public override bool Equals(object obj)
{
if (obj == null) return false;
Part objAsPart = obj as Part;
if (objAsPart == null) return false;
else return Equals(objAsPart);
}
public override int GetHashCode()
{
return PartId;
}
public bool Equals(Part other)
{
if (other == null) return false;
return (this.PartId.Equals(other.PartId));
}
// Should also override == and != operators.
}
public class Example
{
public static void Main()
{
// Create a list of parts.
List<Part> parts = new List<Part>();

// Add parts to the list.
parts.Add(new Part() { PartName = "crank arm", PartId = 1234 });
parts.Add(new Part() { PartName = "chain ring", PartId = 1334 });
parts.Add(new Part() { PartName = "regular seat", PartId = 1434 });
parts.Add(new Part() { PartName = "banana seat", PartId = 1444 });
parts.Add(new Part() { PartName = "cassette", PartId = 1534 });
parts.Add(new Part() { PartName = "shift lever", PartId = 1634 }); ;

// Write out the parts in the list. This will call the overridden ToString method
// in the Part class.
Console.WriteLine();
foreach (Part aPart in parts)
{
Console.WriteLine(aPart);
}

// Check the list for part #1734. This calls the IEquatable.Equals method
// of the Part class, which checks the PartId for equality.
Console.WriteLine("\nContains: Part with Id=1734: {0}",
parts.Contains(new Part { PartId = 1734, PartName = "" }));

// Find items where name contains "seat".
Console.WriteLine("\nFind: Part where name contains \"seat\": {0}",
parts.Find(x => x.PartName.Contains("seat")));

// Check if an item with Id 1444 exists.
Console.WriteLine("\nExists: Part with Id=1444: {0}",
parts.Exists(x => x.PartId == 1444));

/*This code example produces the following output:

ID: 1234   Name: crank arm
ID: 1334   Name: chain ring
ID: 1434   Name: regular seat
ID: 1444   Name: banana seat
ID: 1534   Name: cassette
ID: 1634   Name: shift lever

Contains: Part with Id=1734: False

Find: Part where name contains "seat": ID: 1434   Name: regular seat

Exists: Part with Id=1444: True
*/
}
}
``````
``````Imports System.Collections.Generic
' Simple business object. A PartId is used to identify a part
' but the part name can change.
Public Class Part
Implements IEquatable(Of Part)
Public Property PartName() As String
Get
Return m_PartName
End Get
Set(value As String)
m_PartName = Value
End Set
End Property
Private m_PartName As String
Public Property PartId() As Integer
Get
Return m_PartId
End Get
Set(value As Integer)
m_PartId = Value
End Set
End Property
Private m_PartId As Integer

Public Overrides Function ToString() As String
Return Convert.ToString("ID: " & PartId & "   Name: ") & PartName
End Function
Public Overrides Function Equals(obj As Object) As Boolean
If obj Is Nothing Then
Return False
End If
Dim objAsPart As Part = TryCast(obj, Part)
If objAsPart Is Nothing Then
Return False
Else
Return Equals(objAsPart)
End If
End Function
Public Overrides Function GetHashCode() As Integer
Return PartId
End Function
Public Overloads Function Equals(other As Part) As Boolean _
Implements IEquatable(Of Part).Equals
If other Is Nothing Then
Return False
End If
Return (Me.PartId.Equals(other.PartId))
End Function
' Should also override == and != operators.
End Class
Public Class Example
Public Shared Sub Main()
' Create a list of parts.
Dim parts As New List(Of Part)()

' Add parts to the list.
.PartName = "crank arm", _
.PartId = 1234 _
})
.PartName = "chain ring", _
.PartId = 1334 _
})
.PartName = "regular seat", _
.PartId = 1434 _
})
.PartName = "banana seat", _
.PartId = 1444 _
})
.PartName = "cassette", _
.PartId = 1534 _
})
.PartName = "shift lever", _
.PartId = 1634 _
})

' Write out the parts in the list. This will call the overridden ToString method
' in the Part class.
Console.WriteLine()
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next

' Check the list for part #1734. This calls the IEquatable.Equals method
' of the Part class, which checks the PartId for equality.
Console.WriteLine(vbLf & "Contains: Part with Id=1734: {0}",
parts.Contains(New Part() With { _
.PartId = 1734, _
.PartName = "" _
}))

' Find items where name contains "seat".
Console.WriteLine(vbLf & "Find: Part where name contains ""seat"": {0}",
parts.Find(Function(x) x.PartName.Contains("seat")))

' Check if an item with Id 1444 exists.
Console.WriteLine(vbLf & "Exists: Part with Id=1444: {0}",
parts.Exists(Function(x) x.PartId = 1444))

'This code example produces the following output:
'
'        ID: 1234   Name: crank arm
'        ID: 1334   Name: chain ring
'        ID: 1434   Name: regular seat
'        ID: 1444   Name: banana seat
'        ID: 1534   Name: cassette
'        ID: 1634   Name: shift lever
'
'        Contains: Part with Id=1734: False
'
'        Find: Part where name contains "seat": ID: 1434   Name: regular seat
'
'        Exists: Part with Id=1444: True
'

End Sub
End Class
``````

AList<T>文字列の作成、"saurus"で終わる (位置 1 と 5) での 2 つの 8 恐竜の名前を含むです。A List<T> of strings is created, containing 8 dinosaur names, two of which (at positions 1 and 5) end with "saurus". この例では、という名前の検索述語メソッドも定義します`EndsWithSaurus`、文字列パラメーターを受け入れるし、ブール値を返しますが、入力文字列では"かどうかを示すを値します。The example also defines a search predicate method named `EndsWithSaurus`, which accepts a string parameter and returns a Boolean value indicating whether the input string ends in "saurus".

FindFindLast、およびFindAllメソッドを使用して検索の述語メソッドを使用して、一覧を検索し、 RemoveAll "saurus"で終わるすべてのエントリを削除するメソッドを使用します。The Find, FindLast, and FindAll methods are used to search the list with the search predicate method, and then the RemoveAll method is used to remove all entries ending with "saurus".

C# および Visual Basic の場合でない作成に必要な`Predicate<string>`デリゲート (`Predicate(Of String)` Visual Basic で) 明示的にします。In C# and Visual Basic, it is not necessary to create the `Predicate<string>` delegate (`Predicate(Of String)` in Visual Basic) explicitly. これらの言語では、コンテキストから適切なデリゲート推測し、自動的に作成します。These languages infer the correct delegate from context and create it automatically.

``````using namespace System;
using namespace System::Collections::Generic;

// Search predicate returns true if a string ends in "saurus".
bool EndsWithSaurus(String^ s)
{
return s->ToLower()->EndsWith("saurus");
};

void main()
{
List<String^>^ dinosaurs = gcnew List<String^>();

Console::WriteLine();
for each(String^ dinosaur in dinosaurs )
{
Console::WriteLine(dinosaur);
}

Console::WriteLine("\nTrueForAll(EndsWithSaurus): {0}",
dinosaurs->TrueForAll(gcnew Predicate<String^>(EndsWithSaurus)));

Console::WriteLine("\nFind(EndsWithSaurus): {0}",
dinosaurs->Find(gcnew Predicate<String^>(EndsWithSaurus)));

Console::WriteLine("\nFindLast(EndsWithSaurus): {0}",
dinosaurs->FindLast(gcnew Predicate<String^>(EndsWithSaurus)));

Console::WriteLine("\nFindAll(EndsWithSaurus):");
List<String^>^ sublist =
dinosaurs->FindAll(gcnew Predicate<String^>(EndsWithSaurus));

for each(String^ dinosaur in sublist)
{
Console::WriteLine(dinosaur);
}

Console::WriteLine(
"\n{0} elements removed by RemoveAll(EndsWithSaurus).",
dinosaurs->RemoveAll(gcnew Predicate<String^>(EndsWithSaurus)));

Console::WriteLine("\nList now contains:");
for each(String^ dinosaur in dinosaurs)
{
Console::WriteLine(dinosaur);
}

Console::WriteLine("\nExists(EndsWithSaurus): {0}",
dinosaurs->Exists(gcnew Predicate<String^>(EndsWithSaurus)));
}

/* This code example produces the following output:

Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops

TrueForAll(EndsWithSaurus): False

Find(EndsWithSaurus): Amargasaurus

FindLast(EndsWithSaurus): Dilophosaurus

FindAll(EndsWithSaurus):
Amargasaurus
Dilophosaurus

2 elements removed by RemoveAll(EndsWithSaurus).

List now contains:
Compsognathus
Oviraptor
Velociraptor
Deinonychus
Gallimimus
Triceratops

Exists(EndsWithSaurus): False
*/
``````
``````using System;
using System.Collections.Generic;

public class Example
{
public static void Main()
{
List<string> dinosaurs = new List<string>();

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
Console.WriteLine(dinosaur);
}

Console.WriteLine("\nTrueForAll(EndsWithSaurus): {0}",
dinosaurs.TrueForAll(EndsWithSaurus));

Console.WriteLine("\nFind(EndsWithSaurus): {0}",
dinosaurs.Find(EndsWithSaurus));

Console.WriteLine("\nFindLast(EndsWithSaurus): {0}",
dinosaurs.FindLast(EndsWithSaurus));

Console.WriteLine("\nFindAll(EndsWithSaurus):");
List<string> sublist = dinosaurs.FindAll(EndsWithSaurus);

foreach(string dinosaur in sublist)
{
Console.WriteLine(dinosaur);
}

Console.WriteLine(
"\n{0} elements removed by RemoveAll(EndsWithSaurus).",
dinosaurs.RemoveAll(EndsWithSaurus));

Console.WriteLine("\nList now contains:");
foreach(string dinosaur in dinosaurs)
{
Console.WriteLine(dinosaur);
}

Console.WriteLine("\nExists(EndsWithSaurus): {0}",
dinosaurs.Exists(EndsWithSaurus));
}

// Search predicate returns true if a string ends in "saurus".
private static bool EndsWithSaurus(String s)
{
return s.ToLower().EndsWith("saurus");
}
}

/* This code example produces the following output:

Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops

TrueForAll(EndsWithSaurus): False

Find(EndsWithSaurus): Amargasaurus

FindLast(EndsWithSaurus): Dilophosaurus

FindAll(EndsWithSaurus):
Amargasaurus
Dilophosaurus

2 elements removed by RemoveAll(EndsWithSaurus).

List now contains:
Compsognathus
Oviraptor
Velociraptor
Deinonychus
Gallimimus
Triceratops

Exists(EndsWithSaurus): False
*/
``````
``````Imports System
Imports System.Collections.Generic

Public Class Example

Public Shared Sub Main()

Dim dinosaurs As New List(Of String)

Console.WriteLine()
For Each dinosaur As String In dinosaurs
Console.WriteLine(dinosaur)
Next

Console.WriteLine(vbLf & _

Console.WriteLine(vbLf & _

Console.WriteLine(vbLf & _

Console.WriteLine(vbLf & _
Dim sublist As List(Of String) = _

For Each dinosaur As String In sublist
Console.WriteLine(dinosaur)
Next

Console.WriteLine(vbLf & _
"{0} elements removed by RemoveAll(AddressOf EndsWithSaurus).", _

Console.WriteLine(vbLf & "List now contains:")
For Each dinosaur As String In dinosaurs
Console.WriteLine(dinosaur)
Next

Console.WriteLine(vbLf & _

End Sub

' Search predicate returns true if a string ends in "saurus".
Private Shared Function EndsWithSaurus(ByVal s As String) _
As Boolean

Return s.ToLower().EndsWith("saurus")
End Function
End Class

' This code example produces the following output:
'
'Compsognathus
'Amargasaurus
'Oviraptor
'Velociraptor
'Deinonychus
'Dilophosaurus
'Gallimimus
'Triceratops
'
'
'
'
'Amargasaurus
'Dilophosaurus
'
'2 elements removed by RemoveAll(AddressOf EndsWithSaurus).
'
'List now contains:
'Compsognathus
'Oviraptor
'Velociraptor
'Deinonychus
'Gallimimus
'Triceratops
'
Predicate<T>を返すメソッドにデリゲート`true`デリゲートで定義されている条件に一致するオブジェクトが渡された場合。The Predicate<T> is a delegate to a method that returns `true` if the object passed to it matches the conditions defined in the delegate. 現在の要素List<T>に個別に渡される、Predicate<T>一致が見つかったときに、デリゲートと処理が停止します。The elements of the current List<T> are individually passed to the Predicate<T> delegate, and processing is stopped when a match is found.