Enumerable.All(Of TSource) Method
Determines whether all elements of a sequence satisfy a condition.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
'Declaration <ExtensionAttribute> _ Public Shared Function All(Of TSource) ( _ source As IEnumerable(Of TSource), _ predicate As Func(Of TSource, Boolean) _ ) As Boolean
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
- Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) that contains the elements to apply the predicate to.
- predicate
- Type: System.Func(Of TSource, Boolean)
A function to test each element for a condition.
Return Value
Type: System.Booleantrue if every element of the source sequence passes the test in the specified predicate, or if the sequence is empty; otherwise, false.
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(Of TSource). When you use instance method syntax to call this method, omit the first parameter.| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate is Nothing. |
Note: |
|---|
This method does not return all the elements of a collection. Instead, it determines whether all the elements of a collection satisfy a condition. |
The enumeration of source is stopped as soon as the result can be determined.
In Visual Basic query expression syntax, an Aggregate Into All() clause translates to an invocation of All(Of TSource).
The following code example demonstrates how to use All(Of TSource) to determine whether all the elements in a sequence satisfy a condition.
Structure Pet Public Name As String Public Age As Integer End Structure Sub AllEx() ' Create an array of Pets. Dim pets() As Pet = _ {New Pet With {.Name = "Barley", .Age = 2}, _ New Pet With {.Name = "Boots", .Age = 4}, _ New Pet With {.Name = "Whiskers", .Age = 7}} ' Determine whether all pet names in the array start with "B". Dim allNames As Boolean = _ pets.All(Function(pet) pet.Name.StartsWith("B")) ' Display the output. Dim text As String = IIf(allNames, "All", "Not all") outputBlock.Text &= text & " pet names start with 'B'." & vbCrLf End Sub ' This code produces the following output: ' ' Not all pet names start with 'B'.
The Boolean value that the All(Of TSource) method returns is typically used in the predicate of a where clause (Where clause in Visual Basic) or a direct call to the Where method. The following example demonstrates this use of the All method.
Structure Pet Public Name As String Public Age As Integer End Structure Structure Person Public LastName As String Public Pets() As Pet End Structure Sub AllEx2() Dim people As New List(Of Person)(New Person() _ {New Person With {.LastName = "Haas", _ .Pets = New Pet() {New Pet With {.Name = "Barley", .Age = 10}, _ New Pet With {.Name = "Boots", .Age = 14}, _ New Pet With {.Name = "Whiskers", .Age = 6}}}, _ New Person With {.LastName = "Fakhouri", _ .Pets = New Pet() {New Pet With {.Name = "Snowball", .Age = 1}}}, _ New Person With {.LastName = "Antebi", _ .Pets = New Pet() {New Pet With {.Name = "Belle", .Age = 8}}}, _ New Person With {.LastName = "Philips", _ .Pets = New Pet() {New Pet With {.Name = "Sweetie", .Age = 2}, _ New Pet With {.Name = "Rover", .Age = 13}}}}) ' Determine which people have pets that are all older than 5. Dim names = From person In people _ Where person.Pets.All(Function(pet) pet.Age > 5) _ Select person.LastName For Each name As String In names outputBlock.Text &= name & vbCrLf Next ' This code produces the following output: ' ' Haas ' Antebi End Sub
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