In visual basic, Dictionary is a generic type of collection and it is useful to store a collection of key/value pairs that are organized based on the key. The dictionary in visual basic will allow storing only the strongly-typed objects i.e. the key/value pairs of the specified data type.
In visual basic, while storing the elements in the dictionary object, we must need to make sure that the keys are unique because the dictionary object will allow us to store duplicate values but the keys must be unique.
The size of the dictionary object will vary dynamically so we can add or remove elements from the dictionary object based on our requirements.
In visual basic, the dictionary object is same as hashtable object but the only difference is the dictionary object is useful to store a key-value pair of the same data type elements.
In visual basic, the dictionary is a generic type of collection and it is provided by System.Collections.Generic namespace.
As discussed, the collection is a class so to define a dictionary, we just need to declare an instance of dictionary class before we perform any operations such as add, delete, etc. like as shown below.
Dim dct As Dictionary(Of TKey, TValue) = New Dictionary(Of TKey, TValue)()
If you observe the above dictionary declaration, we created a generic dictionary (dct) with an instance of dictionary class using type parameters (TKey, TValue) as placeholders within brackets (Of TKey, TValue).
Here, the brackets will indicate that the dictionary is a generic type and type parameter TKey is to represent a type of keys to be accepted by dictionary and TValue is used to represent a type of values to be accepted by dictionary.
In visual basic, the generic dictionary (Dictionary(Of T)) is an implementation of IDictionary(Of TKey, TValue) interface so we can also use IDictionary(Of TKey, TValue) interface to create an object of the generic dictionary (Dictionary(Of TKey, TValue)) like as shown below.
Dim dct As IDictionary(Of TKey, TValue) = New Dictionary(Of TKey, TValue)()
Following is the example of initializing a generic dictionary by specifying the required type for key and value.
Dim dct As Dictionary(Of String, Integer) = New Dictionary(Of String, Integer)()
If you observe the above example, we defined a dictionary (dct) with the required key and value types to store. Here, the dictionary object will store a key of string type and value of int type.
The following are some of the commonly used properties of the dictionary object in a visual basic programming language.
| Property | Description |
|---|---|
| Count | It is used to get the number of key/value pair elements in the dictionary. |
| Item[TKey] | It is used to get or set the value associated with the specified key. |
| Keys | It is used to get a collection of keys in the dictionary. |
| Values | It is used to get a collection of values in a dictionary. |
The following are some of the commonly used methods of the generic dictionary to perform add, search, insert, delete or sort operations in a visual basic programming language.
| Method | Description |
|---|---|
| Add | It is used to add elements to the dictionary object with a specified key and value. |
| Clear | It will remove all the keys and values from the Dictionary<TKey, TValue>. |
| ContainsKey | It is used to determine whether the specified key exists in Dictionary<TKey, TValue> or not. |
| ContainsValue | It is used to determine whether the specified value exists in Dictionary<TKey, TValue> or not. |
| Remove | It is used to remove an element from Dictionary<TKey, TValue> with the specified key. |
| TryGetValue | It is used to get the value associated with the specified key. |
As discussed, while adding elements to the dictionary object we need to make sure that there will not be any duplicate keys.
Following is the example of adding a key/value pair elements to dictionary objects in different ways.
Module Module1
Sub Main(ByVal args As String())
' Create a new dictionary with int keys and string values.
Dim dct As Dictionary(Of Integer, String) = New Dictionary(Of Integer, String)()
' Add elements to the dictionary object
' No duplicate keys allowed but values can be duplicate
dct.Add(1, "Suresh")
dct.Add(4, "Rohini")
dct.Add(2, "Trishi")
dct.Add(3, Nothing)
' Another way to add elements.
' If key Not exist, then that key adds a new key/value pair.
dct(5) = "Trishi"
' Add method throws an exception if key already in the dictionary
Try
dct.Add(2, "Praveen")
Catch __unusedArgumentException1__ As ArgumentException
Console.WriteLine("An element with Key = '2' already exists.")
End Try
Console.WriteLine("*********Dictionary1 Elements********")
' Accessing elements as KeyValuePair objects
For Each item As KeyValuePair(Of Integer, String) In dct
Console.WriteLine("Key = {0}, Value = {1}", item.Key, item.Value)
Next
' Creating and initializing dictionary
Dim dct2 As Dictionary(Of String, Integer?) = New Dictionary(Of String, Integer?) From {
{"msg2", 1},
{"msg3", 20},
{"msg4", 100},
{"msg1", Nothing}
}
Console.WriteLine("*********Dictionary2 Elements********")
' Accessing elements as KeyValuePair objects
For Each item As KeyValuePair(Of String, Integer?) In dct2
Console.WriteLine("Key = {0}, Value = {1}", item.Key, item.Value)
Next
Console.ReadLine()
End Sub
End Module
If you observe the above example, we are able to define a new generic dictionary (dct, dct2) collections. Here, we added only the defined data type keys and values to the newly created dictionaries (dct, dct2) in different ways.
As discussed, the Add method will throw an exception in case if we try to add a key (2) which is already existing so to handle that exception we used a try-catch block.
When we execute the above visual basic program, we will get the result as shown below.
If you observe the above result, we got an exception when we tried to add a key (2) which is already existing and added a key (5) which is not existing in the dictionary.
In visual basic, we have different ways to access dictionary elements i.e. either by using index positions or by iterating through the list using For / For Each loop.
Following is the example of accessing dictionary elements in different ways.
Module Module1
Sub Main(ByVal args As String())
' Create a new dictionary
Dim dct As Dictionary(Of Integer, String) = New Dictionary(Of Integer, String)()
dct.Add(1, "Suresh")
dct.Add(4, "Rohini")
dct.Add(2, "Trishi")
dct.Add(3, "Praveen")
' Access value with key (not index)
Dim val1 As String = dct(2)
Dim val2 As String = dct(3)
Dim val3 As String = dct(4)
Console.WriteLine("******Access Elements with Keys*****")
Console.WriteLine("Value at Key '2': " & val1)
Console.WriteLine("Value at Key '3': " & val2)
Console.WriteLine("Value at Key '4': " & val3)
Console.WriteLine("*********Access Elements with Foreach Loop********")
For Each item As KeyValuePair(Of Integer, String) In dct
Console.WriteLine("Key = {0}, Value = {1}", item.Key, item.Value)
Next
Console.WriteLine("*********Dictionary Keys********")
For Each item In dct.Keys
Console.WriteLine("Key = {0}", item)
Next
Console.WriteLine("*********Dictionary Values********")
For Each item In dct.Values
Console.WriteLine("Value = {0}", item)
Next
Console.ReadLine()
End Sub
End Module
If you observe the above example, we are accessing dictionary elements in different ways by using keys and For Each loop based on our requirements.
When we execute the above visual basic program, we will get the result as shown below.
In visual basic, by using Remove() method we can delete a key/value pair from dictionary object.
Following is the example of deleting elements from the dictionary object in a visual basic programming language.
Module Module1
Sub Main(ByVal args As String())
' Create a new dictionary
Dim dct As Dictionary(Of Integer, String) = New Dictionary(Of Integer, String)()
dct.Add(1, "Suresh")
dct.Add(4, "Rohini")
dct.Add(2, "Trishi")
dct.Add(3, "Praveen")
dct.Add(5, "Sateesh")
' Remove element with key (not index)
dct.Remove(3)
dct.Remove(5)
Console.WriteLine("*********Access Dictionary Elements********")
Console.WriteLine()
For Each item As KeyValuePair(Of Integer, String) In dct
Console.WriteLine("Key = {0}, Value = {1}", item.Key, item.Value)
Next
Console.ReadLine()
End Sub
End Module
If you observe the above example, we used the Remove() method to delete a particular key of the element from a dictionary.
When we execute the above visual basic program, we will get the result as shown below.
By using ContainsKey() and ContainsValue() methods, we can check whether the specified key/value elements exist in the dictionary or not. In case, if it exists these methods will return True otherwise False.
Following is the example of using ContainsKey() and ContainsValue() methods to check for an item that exists in the dictionary or not in visual basic.
Module Module1
Sub Main(ByVal args As String())
' Create a new dictionary
Dim dct As Dictionary(Of Integer, String) = New Dictionary(Of Integer, String)()
dct.Add(1, "Suresh")
dct.Add(4, "Rohini")
dct.Add(2, "Trishi")
dct.Add(3, "Praveen")
dct.Add(5, "Sateesh")
Console.WriteLine("Contains Key 2: {0}", dct.ContainsKey(2))
Console.WriteLine("Contains Value 'Tutlane': {0}", dct.ContainsValue("Tutlane"))
Console.ReadLine()
End Sub
End Module
If you observe the above example, we used a ContainsKey() and ContainsValue() methods to check for particular keys and values that exist in the dictionary (dct) or not.
When we execute the above visual basic program, we will get the result as shown below.
Contains Key 2: True
Contains Value 'Tutlane': False
The following are the important points which we need to remember about the dictionary in visual basic.
The following are the main differences between hashtable and dictionary in a visual basic programming language.