List(Of T).IndexOf Method (T, Int32, Int32)
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Searches for the specified object and returns the zero-based index of the first occurrence within the range of elements in the List(Of T) that starts at the specified index and contains the specified number of elements.
Assembly: mscorlib (in mscorlib.dll)
'Declaration Public Function IndexOf ( _ item As T, _ index As Integer, _ count As Integer _ ) As Integer
Parameters
- item
- Type: T
The object to locate in the List(Of T). The value can be Nothing for reference types.
- index
- Type: System.Int32
The zero-based starting index of the search.
- count
- Type: System.Int32
The number of elements in the section to search.
Return Value
Type: System.Int32The zero-based index of the first occurrence of item within the range of elements in the List(Of T) that starts at index and contains count number of elements, if found; otherwise, –1.
| Exception | Condition |
|---|---|
| ArgumentOutOfRangeException | index is outside the range of valid indexes for the List(Of T). -or- count is less than 0. -or- index and count do not specify a valid section in the List(Of T). |
The List(Of T) is searched forward starting at index and ending at index plus count minus 1, if count is greater than 0.
This method determines equality using the default equality comparer EqualityComparer(Of T).Default for T, the type of values in the list.
This method performs a linear search; therefore, this method is an O(n) operation, where n is count.
The following code example demonstrates all three overloads of the IndexOf method. A List(Of T) of strings is created, with one entry that appears twice, at index location 0 and index location 5. The IndexOf(T) method overload searches the list from the beginning, and finds the first occurrence of the string. The IndexOf(T, Int32) method overload is used to search the list beginning with index location 3 and continuing to the end of the list, and finds the second occurrence of the string. Finally, the IndexOf(T, Int32, Int32) method overload is used to search a range of two entries, beginning at index location two; it returns –1 because there are no instances of the search string in that range.
Imports System.Collections.Generic Public Class Example Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock) Dim dinosaurs As New List(Of String) dinosaurs.Add("Tyrannosaurus") dinosaurs.Add("Amargasaurus") dinosaurs.Add("Mamenchisaurus") dinosaurs.Add("Brachiosaurus") dinosaurs.Add("Deinonychus") dinosaurs.Add("Tyrannosaurus") dinosaurs.Add("Compsognathus") outputBlock.Text &= vbCrLf For Each dinosaur As String In dinosaurs outputBlock.Text &= dinosaur & vbCrLf Next outputBlock.Text &= String.Format(vbLf & _ "IndexOf(""Tyrannosaurus""): {0}", _ dinosaurs.IndexOf("Tyrannosaurus")) & vbCrLf outputBlock.Text &= String.Format(vbLf & _ "IndexOf(""Tyrannosaurus"", 3): {0}", _ dinosaurs.IndexOf("Tyrannosaurus", 3)) & vbCrLf outputBlock.Text &= String.Format(vbLf & _ "IndexOf(""Tyrannosaurus"", 2, 2): {0}", _ dinosaurs.IndexOf("Tyrannosaurus", 2, 2)) & vbCrLf End Sub End Class ' This code example produces the following output: ' 'Tyrannosaurus 'Amargasaurus 'Mamenchisaurus 'Brachiosaurus 'Deinonychus 'Tyrannosaurus 'Compsognathus ' 'IndexOf("Tyrannosaurus"): 0 ' 'IndexOf("Tyrannosaurus", 3): 5 ' 'IndexOf("Tyrannosaurus", 2, 2): -1