List(T).FindAll 方法 (System.Collections.Generic)

.NET Framework 類別庫

List<(Of <(T>)>)..::.FindAll 方法

更新：2007 年 11 月

擷取符合指定之述詞所定義的條件之所有元素。

命名空間： System.Collections.Generic
組件： mscorlib (在 mscorlib.dll 中)

語法

Visual Basic (宣告)

Public Function FindAll ( _
    match As Predicate(Of T) _
) As List(Of T)

Visual Basic (使用方式)

Dim instance As List
Dim match As Predicate(Of T)
Dim returnValue As List(Of T)

returnValue = instance.FindAll(match)

public List<T> FindAll(
    Predicate<T> match
)

Visual C++

public:
List<T>^ FindAll(
    Predicate<T>^ match
)

public List<T> FindAll(
    Predicate<T> match
)

JScript

public function FindAll(
    match : Predicate<T>
) : List<T>

參數

match: 型別：System..::.Predicate<(Of <(T>)>)
定義要搜尋元素之條件的 Predicate<(Of <(T>)>) 委派。

傳回值

型別：System.Collections.Generic..::.List<(Of <(T>)>)
List<(Of <(T>)>)，其中包含符合指定之述詞所定義的條件之所有元素 (如果有找到的話)，否則為空的 List<(Of <(T>)>)。

例外狀況

例外狀況	條件
ArgumentNullException	match 為 nullNothingnullptrNull 參照 (即 Visual Basic 中的 Nothing)。

備註

Predicate<(Of <(T>)>) 是方法的委派，如果傳遞給它的物件與委派中定義的條件相符，即傳回 true。目前 List<(Of <(T>)>) 的元素會個別傳遞給 Predicate<(Of <(T>)>) 委派，且符合條件的元素會儲存在傳回的 List<(Of <(T>)>) 中。

這個方法會執行線性搜尋；因此，這個方法是 O(n) 運算，其中 n 是 Count。

範例

下列程式碼範例將示範 Find、FindLast 和 FindAll 方法。已建立字串的 List<(Of <(T>)>)，包含 8 個恐龍 (Dinosaur) 名稱，其中兩個 (在位置 1 和 5) 以 "saurus" 結尾。程式碼範例也會定義搜尋述詞 (Predicate) 方法 (名稱為 EndsWithSaurus)，這麼做會接受字串參數並傳回布林值 (Boolean)，指出輸入的字串是否以 "saurus" 結尾。

Find 方法會從開頭周遊清單，將每個項目依次傳遞至 EndsWithSaurus 方法。搜尋在 EndsWithSaurus 方法針對元素 "Amargasaurus" 傳回 true 時停止。

注意事項：
在 C# 和 Visual Basic 中，不需要明確建立 Predicate<string> 委派 (在 Visual Basic 中為 Predicate(Of String))。這些語言會從內容推斷並自動建立正確的委派。

FindLast 方法會用來從結尾處反向搜尋清單。它會尋找在位置 5 的元素 "Dilophosaurus"。FindAll 方法會用於傳回 List<(Of <(T>)>)，其中包含所有以 "saurus" 結尾的元素。元素便會顯示。

最後，RemoveAll 方法會用來移除所有以 "saurus" 結尾的元素，而 Exists 方法則證實所有這一類的字串已消失。

Visual Basic

Imports System
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)

        dinosaurs.Add("Compsognathus")
        dinosaurs.Add("Amargasaurus")
        dinosaurs.Add("Oviraptor")
        dinosaurs.Add("Velociraptor")
        dinosaurs.Add("Deinonychus")
        dinosaurs.Add("Dilophosaurus")
        dinosaurs.Add("Gallimimus")
        dinosaurs.Add("Triceratops")

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

        Console.WriteLine(vbLf & _
            "TrueForAll(AddressOf EndsWithSaurus: {0}", _
            dinosaurs.TrueForAll(AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "Find(AddressOf EndsWithSaurus): {0}", _
            dinosaurs.Find(AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "FindLast(AddressOf EndsWithSaurus): {0}", _
            dinosaurs.FindLast(AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "FindAll(AddressOf EndsWithSaurus):")
        Dim sublist As List(Of String) = _
            dinosaurs.FindAll(AddressOf EndsWithSaurus)

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

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

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

        Console.WriteLine(vbLf & _
            "Exists(AddressOf EndsWithSaurus): {0}", _
            dinosaurs.Exists(AddressOf EndsWithSaurus))

    End Sub

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

        ' AndAlso prevents evaluation of the second Boolean
        ' expression if the string is so short that an error
        ' would occur.
        If (s.Length > 5) AndAlso _
            (s.Substring(s.Length - 6).ToLower() = "saurus") Then
            Return True
        Else
            Return False
        End If
    End Function
End Class

' This code example produces the following output:
'
'Compsognathus
'Amargasaurus
'Oviraptor
'Velociraptor
'Deinonychus
'Dilophosaurus
'Gallimimus
'Triceratops
'
'TrueForAll(AddressOf EndsWithSaurus: False
'
'Find(AddressOf EndsWithSaurus): Amargasaurus
'
'FindLast(AddressOf EndsWithSaurus): Dilophosaurus
'
'FindAll(AddressOf EndsWithSaurus):
'Amargasaurus
'Dilophosaurus
'
'2 elements removed by RemoveAll(AddressOf EndsWithSaurus).
'
'List now contains:
'Compsognathus
'Oviraptor
'Velociraptor
'Deinonychus
'Gallimimus
'Triceratops
'
'Exists(AddressOf EndsWithSaurus): False

using System;
using System.Collections.Generic;

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

        dinosaurs.Add("Compsognathus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("Oviraptor");
        dinosaurs.Add("Velociraptor");
        dinosaurs.Add("Deinonychus");
        dinosaurs.Add("Dilophosaurus");
        dinosaurs.Add("Gallimimus");
        dinosaurs.Add("Triceratops");

        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)
    {
        if ((s.Length > 5) && 
            (s.Substring(s.Length - 6).ToLower() == "saurus"))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

/* 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
 */

Visual C++

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

// Search predicate returns true if a string ends in "saurus".
bool EndsWithSaurus(String^ s)
{
    if ((s->Length > 5) && 
        (s->Substring(s->Length - 6)->ToLower() == "saurus"))
    {
        return true;
    }
    else
    {
        return false;
    }
};

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

    dinosaurs->Add("Compsognathus");
    dinosaurs->Add("Amargasaurus");
    dinosaurs->Add("Oviraptor");
    dinosaurs->Add("Velociraptor");
    dinosaurs->Add("Deinonychus");
    dinosaurs->Add("Dilophosaurus");
    dinosaurs->Add("Gallimimus");
    dinosaurs->Add("Triceratops");

    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
 */

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