Dictionary Methods
The Dictionary class is a generic collection and provides all common methods to add, remove, find and replace items in the collection.
Add Items
The Add method adds an item to the Dictionary collection in form of a key and a value. The following code snippet creates a Dictionary and adds an item to it by using the Add method.
Dim StudentDetailList As New Dictionary(Of String, Int16)()
StudentDetailList.Add("Mahesh", 35)
Alternatively, we can use the Item property. If the key does not exist in the collection, a new item is added. If the same key already exists in the collection, the item value is updated to the new value. The following code snippet adds an item and updates the existing item in the collection.
StudentDetailList("Mahesh") = 20
StudentDetailList("Raj") = 9
Remove Item
The Remove method removes an item with the specified key from the collection. The following code snippet removes an item.
' Remove item with key = 'Mahesh'
StudentDetailList.Remove("Mahesh")
The Clear method removes all items from the collection. The following code snippet removes all items by calling the Clear method.
' Remove all items
StudentDetailList.Clear()
Find a Key
The ContainsKey method checks if a key is already exists in the dictionary. The following code snippet checks if a key is already exits and if not, add one.
If Not StudentDetailList.ContainsKey("Mahesh") Then
StudentDetailList("Mahesh") = 20
End If
Find a Value
The ContainsValue method checks if a value is already exists in the dictionary. The following code snippet checks if a value is already exits.
If Not StudentDetailList.ContainsValue(9) Then
Console.WriteLine("Item found")
End If
Here is the complete sample code showing how to use these methods.
Imports System.Collections.Generic
Module Module1
Sub Main()
' Create a dictionary with string key and Int16 value pair
Dim StudentDetailList As New Dictionary(Of String, Int16)()
StudentDetailList.Add("Mahesh", 35)
StudentDetailList.Add("Raj", 25)
StudentDetailList.Add("Suresh", 29)
StudentDetailList.Add("Nitin", 21)
StudentDetailList.Add("Aman", 84)
' Count
Console.WriteLine("Count: {0}", StudentDetailList.Count)
' Set Item value
StudentDetailList("Raj") = 9
If Not StudentDetailList.ContainsKey("Mahesh") Then
StudentDetailList("Mahesh") = 20
End If
If Not StudentDetailList.ContainsValue(29) Then
Console.WriteLine()
Console.WriteLine("Item found")
End If
' Read all items
Console.WriteLine("All items:")
Console.WriteLine()
For Each student As KeyValuePair(Of String, Int16) In StudentDetailList
Console.WriteLine("Key: {0}, Value: {1}", student.Key, student.Value)
Next
' Remove item with key = 'Aman'
StudentDetailList.Remove("Aman")
Console.WriteLine()
Console.WriteLine("List after removal of item with key='Aman'")
For Each student As KeyValuePair(Of String, Int16) In StudentDetailList
Console.WriteLine("Key: {0}, Value: {1}", student.Key, student.Value)
Next
' Remove all items
StudentDetailList.Clear()
For Each student As KeyValuePair(Of String, Int16) In StudentDetailList
Console.WriteLine("Key: {0}, Value: {1}", student.Key, student.Value)
Next
Console.WriteLine("All Items removed")
Console.ReadLine()
End Sub
End Module
Output: