REGISTRY

The system registry is a hierarchical database that stores values for applications on the system. The hierarchy’s root is named MyComputer and is divided into the several subtrees that are also called hives. Which hives are available depends on your operating system. The following table summarizes the most commonly available hives. (The “HKEY” part of each name stands for “hive key.”)

Depending on your operating system, the registry may also contain the unsupported keys HKEY_PERFORMANCE_DATA, HKEY_PERFORMANCE_NLSTEXT, and HKEY_ PERFORMANCE_TEXT.

Many applications store information in the registry. The HKEY_CURRENT_USER subtree is particularly useful for storing individual users’ preferences and other configuration information.

Lately, the registry has gone out of style for saving configuration information. Microsoft now recommends that you store this kind of data locally within a user’s data storage area. This makes sense because it makes it easier to copy the settings (they’re just files), helps reduce clutter in the registry, and reduces the chances that mistakes will corrupt the registry. You can store this information in configuration files (see the section “Configuration Files” later in this chapter) or XML files.

Visual Basic provides two main ways to access the registry. First, you can use the Visual Basic native registry methods. Second, you can use the tools in the My.Computer.Registry namespace. These two methods are described in the following sections.

You can also use API functions to manipulate the registry. These are more complicated and not generally necessary because the My.Computer.Registry namespace contains some very powerful tools, so they are not described here.

Native Visual Basic Registry Methods

Visual Basic provides four methods for saving and reading registry values for a particular application: SaveSetting, GetSetting, GetAllSettings, and DeleteSetting.

The SaveSetting method saves a value into a registry key. This routine takes as parameters the name of the application, a section name, the setting’s name, and the setting’s value. For example, the following code saves the value stored in the MapDirectory variable in the RegistrySettings application’s Config section with the name MapDirectory:

SaveSetting("RegistrySettings", "Config", "MapDirectory",
    MapDirectory)

SaveSetting automatically creates the application and section areas in the registry if they don’t already exist.

This value is saved at the following registry location. This is all one name; it just doesn’t fit on one line here:

HKEY_CURRENT_USERSoftwareVB and VBA Program Settings
    RegistrySettingsConfigMapDirectory

If you use the Visual Basic SaveSetting, GetSetting, GetAllSettings, and DeleteSetting methods, you don’t need to worry about the first part of this registry path. You only need to remember the application name, section name, and setting name.

The GetSetting function retrieves a registry value. It takes as parameters the application name, section name, and setting name you used to save the value. It can optionally take a default value to return if the setting doesn’t exist in the registry. The following code displays the value saved by the previous call to SaveSetting. If no value is saved in the registry, it displays the string <none>.

MessageBox.Show(GetSetting("RegistrySettings", "Config", "MapDirectory",
 "<none>"))

The GetAllSettings function returns a two-dimensional array of name and value pairs for a registry section. The following code uses GetAllSettings to fetch the values stored in the RegistrySettings application’s Config section. It loops through the results, displaying the setting names and values.

Dim settings As String(,) = GetAllSettings("RegistrySettings", "Config")
For i As Integer = 0 To settings.GetUpperBound(0)
    Debug.WriteLine(settings(i, 0) & " = " & settings(i, 1))
Next i

If an application needs to use all of the settings in a section, GetAllSettings may be faster than using GetSetting repeatedly.

The DeleteSetting method removes a setting, a section, or an entire application’s setting area from the registry. The following code shows how to remove each of those kinds of items:

' Remove the RegistrySettings/Config/CurrentDirectory setting.
DeleteSetting("RegistrySettings", "Config", "CurrentDirectory")
 
' Remove the RegistrySettings/Config section.
DeleteSetting("RegistrySettings", "Config")
 
' Remove all of the RegistrySettings application's settings.
DeleteSetting("RegistrySettings")

Example program RegistrySettings demonstrates each of Visual Basic’s Registry commands.

My.Computer.Registry

The My.Computer.Registry namespace provides objects that manipulate the registry. My.Computer.Registry has seven properties that refer to objects of type RegistryKey. The following table lists these objects and the corresponding registry subtrees:

The program can use these RegistryKey objects to work with the corresponding registry subtree. The following table describes the most useful properties and methods provided by the RegistryKey class:

The following example opens the HKEY_CURRENT_USERSoftwareVB and VBA Program SettingsRegistrySettingsConfig key. It reads the CurrentDirectory value from that key using the default value C: and saves the result in the variable current_directory. It closes the key and then uses the DeleteSubKey method to delete the RegistrySettings application’s Config section.

' Open the application's Config subkey.
Dim config_section As Microsoft.Win32.RegistryKey =
    My.Computer.Registry.CurrentUser.OpenSubKey(
        "SoftwareVB and VBA Program SettingsRegistrySettingsConfig")
 
' Get the CurrentDirectory value.
Dim current_directory As String =
    CType(config_section.GetValue("CurrentDirectory", "C:"), String)
 
' Close the subkey.
config_section.Close()
 
' Delete the application's whole Config section.
My.Computer.Registry.CurrentUser.DeleteSubKey(
    "SoftwareVB and VBA Program SettingsRegistrySettingsConfig")

The following code shows the equivalent operations using the native registry methods of Visual Basic:

 ' Get the CurrentDirectory value.
Dim current_directory As String =
GetSetting("RegistrySettings", "Config", "CurrentDirectory", "C:")
 
' Delete the application's whole Config section.
DeleteSetting("RegistrySettings", "Config")

It is generally easier to use the native registry methods of Visual Basic. Those methods work only with values in the HKEY_CURRENT_USERSoftwareVB and VBA Program Settings Registry subtree, however. If you need to access keys and values outside of this subtree, you must use the My.Computer.Registry objects.

Example program MyComputerRegistry demonstrates many useful My.Computer.Registry operations. It does the same things as program RegistrySettings mentioned in the previous section except it uses My.Computer.Registry instead of Visual Basic’s native registry methods.