List(Of T).IndexOf Method (T, 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 extends from the specified index to the last element.
Assembly: mscorlib (in mscorlib.dll)
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.
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 extends from index to the last element, if found; otherwise, –1.
| Exception | Condition |
|---|---|
| ArgumentOutOfRangeException | index is outside the range of valid indexes for the List(Of T). |
The List(Of T) is searched forward starting at index and ending at the last element.
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 the number of elements from index to the end of the List(Of T).
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