List<T>.TrueForAll(Predicate<T>) Method
Definition
Important
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Determines whether every element in the List<T> matches the conditions defined by the specified predicate.
public:
bool TrueForAll(Predicate<T> ^ match);
public bool TrueForAll (Predicate<T> match);
member this.TrueForAll : Predicate<'T> -> bool
Public Function TrueForAll (match As Predicate(Of T)) As Boolean
Parameters
- match
- Predicate<T>
The Predicate<T> delegate that defines the conditions to check against the elements.
Returns
true
if every element in the List<T> matches the conditions defined by the specified predicate; otherwise, false
. If the list has no elements, the return value is true
.
Exceptions
match
is null
.
Examples
The following example demonstrates the TrueForAll method and several other methods that use Predicate<T> generic delegate.
A List<T> of strings is created, containing 8 dinosaur names, two of which (at positions 1 and 5) end with "saurus". 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".
The TrueForAll method traverses the list from the beginning, passing each element in turn to the EndsWithSaurus
method. The search stops when the EndsWithSaurus
method returns false
.
Note
In C# and Visual Basic, it is not necessary to create the Predicate<string>
delegate (Predicate(Of String)
in Visual Basic) explicitly. 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^>();
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
*/
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)
{
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.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
Return s.ToLower().EndsWith("saurus")
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
Remarks
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. The elements of the current List<T> are individually passed to the Predicate<T> delegate, and processing is stopped when the delegate returns false
for any element. The elements are processed in order, and all calls are made on a single thread.
This method is an O(n) operation, where n is Count.
Applies to
See also
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