How To Use the Dictionary Object with Visual Basic

MORE INFORMATION

The Dictionary is quite similar to the Collection object in both functionality and purpose. The Dictionary, however, offers some functionality that is not available with a Collection. Some of these features include:

• The option to specify a comparison method for Keys. This allows for a case-sensitive Key, for example.
• A method for determining if an object exists in a Dictionary.
• A method for extracting all of the Keys into an Array.
• A method for extracting all of the Items into an Array.
• A method for changing a Key value.
• A method for removing all items from the Dictionary.
• Dictionary Keys are not limited to String datatype.

NOTE: One important difference between the Collection object and the Dictionary object is the behavior of the Item property. If you use the Item property to reference a nonexistent Key in a Collection, you will receive an error. If you use the Item property to reference a nonexistent Key in a Dictionary, that Key will be added to the Dictionary. Use the Exists method to determine whether or not a Key is present in a Dictionary.

The Dictionary object is a component of the Microsoft Scripting library, which does not ship with Visual Basic version 5.0 or later. You can obtain the Microsoft Scripting library (SCRRUN.DLL) by installing one of the following packages:

   Windows Script Host
   Windows NT Option Pack
   IIS 3.0
   Scripting 3.1 upgrade.
				

Step-by-Step Example

1. Start a new Standard EXE project in Visual Basic. (Make sure that the Immediate Window is displayed.) Form1 is created by default.
2. Add a reference to Microsoft Scripting Runtime.
3. Add a standard module to the project.
4. From the Project menu, select Project1.Properties and change the Startup object to Sub Main.
5. Insert the following code into Module1:

         Option Explicit
         Dim dict As Dictionary
   
         Sub Main()
         Dim keyArray, itemArray, element
   
         Set dict = New Dictionary
         With dict
            'set compare mode
            .CompareMode = BinaryCompare
            'add item using named arguments
            .Add Key:="mike", Item:=22
            'add item without named arguments
            .Add "joe", 33
   
            'case sensitivity and Exists method
            'does MIKE exist?
            Debug.Print "MIKE exists = " & .Exists("MIKE")
            'change key value
            .Key("mike") = "MIKE"
            'does MIKE exist?
            Debug.Print "MIKE exists = " & .Exists("MIKE")
   
            'extract keys into variant array
            Debug.Print "Array of Keys"
            keyArray = .Keys
            For Each element In keyArray
               Debug.Print element
            Next
   
            'extract items into variant array
            Debug.Print "Array of Items"
            itemArray = .Items
            For Each element In itemArray
               Debug.Print element
            Next
   
            'empty the dictionary
            .RemoveAll
            Debug.Print dict.Count & " Items in Dictionary"
   
         End With
         Set dict = Nothing
         End Sub
   
   					

6. Run the project. You should see that the initial search for the key fails, then succeeds after the key value is replaced with an uppercase value. Next, you should see the contents of the variant arrays that were extracted from the dictionary using the Keys and Items methods. Last, you see the result of emptying the Dictionary.