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All modern desktop applications save and retrieve
settings using the Windows registry. Storing settings in the registry
saves the user the trouble of re-entering application settings like database
paths etc. In VB 5 and later we have two functions (GetSetting and SaveSetting)
that let us easily save settings to the registry. A significant drawback
with these functions is that they save the setting under the HKEY_CURRENT_USER
hive. When a different user logs onto the PC they need to establish their
own settings. The only way around this is to use the Windows API to create
your own functions to get and save settings under the HKEY_LOCAL_MACHINE
hive. Windows CE for the PocketPC also contains a registry and it can
be used in much the same way as its desktop cousin. The Windows CE API
is also very similar to its desktop counterpart so I was able to port
my VB 6 registry code to eVB without too much trouble. This article discusses
two functions I wrote and how you can easily use them in your application
to save and retrieve settings from the Windows CE registry.
The above screen shot shows the PocketPC registry
key (\pktSoft\TTDS) maintained for an application I have developed. The
registry editor shown in this screen shot is the remote tool accessible
from the eVB IDE.
Design
The GetSetting and SaveSetting functions in VB 6 are
familiar to many developers so I wanted to mimic those two functions in
terms of the parameter lists. Recall that in VB 6 the 2 function calls
are:
SaveSetting (AppName as String, Section as String, Key
a String, Setting as String)
strResult = GetSetting(AppName as String, Section as String, Key as String,
Default as String)
I designed the two eVB functions as follows:
CESaveSetting(strError As String,
ByVal AppName As String, ByVal Section As String, ByVal Key As String,
ByVal Setting As String) As Boolean
CEGetSetting(ByRef strError As Variant, ByVal AppName As String, ByVal
Section As String, ByVal Key As String, ByRef Setting As String) As Boolean
The departures from the intrinsic VB functions are
as follows:
|
Boolean Return
|
All my functions
and methods always return a boolean to the caller indicating success
or fail. Return values are returned as ByRef parameters
|
|
StrError
|
All my methods and
functions return an error string as the first parameter. If the
function return value is True then this string will be empty. If
the function return value is false then this string will contain
the error message.
|
|
GetSetting default
|
I decided not to
implement a default value for CEGetSetting. If the setting comes
back empty your code can take appropriate actions to set a default.
|
|
Hive
|
I always want to
save and get settings from HKEY_LOCAL_MACHINE, not HKEY_CURRENT_USER.
HKEY_CURRENT_USER does not exist in the CE registry.
|
In the registry editor example screen shot above,
the function parameters can be seen as:
| CEGetSetting
Parameter Name |
Value
(as shown in screen shot) |
| AppName[1]
|
SOFTWARE\pktSoft\TTDS
|
| Section
|
Settings
|
| Key
|
DatabasePath
|
| Setting
|
Ce
|
The Windows CE API eVB contains a great little registry
editor that allows you to view the local (PC Windows) registry, the PocketPC
emulator registry and the live PocketPC device registry (via ActiveSync)
all at the same time. Interestingly the eVB emulator will only allow you
to read emulator registry settings but will not allow you to write them.
As a result you need to debug and test registry writing code with the
Run on Target set to Pocket PC (Default Device). eVB also contains
the standard API Viewer application. This utility gives us the correctly
formatted API calls for eVB.
For the registry module we will use 5 API calls:
Public Declare Function RegOpenKeyEx
Lib "Coredll" Alias "RegOpenKeyExW" (ByVal hKey As Long, ByVal lpSubKey
As String, ByVal ulOptions As Long, ByVal samDesired As Long, phkResult
As Long) As Long
Public Declare Function RegQueryValueEx
Lib "Coredll" Alias "RegQueryValueExW" (ByVal hKey As Long, ByVal lpValueName
As String, ByVal lpReserved As Long, lpType As Long, ByVal lpData As String,
lpcbData As Long) As Long
Public Declare Function RegCloseKey
Lib "Coredll" (ByVal hKey As Long) As Long
Public Declare Function RegCreateKeyEx
Lib "Coredll" Alias "RegCreateKeyExW" (ByVal hKey As Long, ByVal lpSubKey
As String, ByVal Reserved As Long, ByVal lpClass As String, ByVal dwOptions
As Long, ByVal samDesired As Long, lpSecurityAttributes As Long, phkResult
As Long, lpdwDisposition As Long) As Long
Public Declare Function RegSetValueEx
Lib "Coredll" Alias "RegSetValueExW" (ByVal hKey As Long, ByVal lpValueName
As String, ByVal Reserved As Long, ByVal dwType As Long, ByVal lpData
As String, ByVal cbData As Long) As Long
I also copied some useful constants from the API Viewer:
Public Const SYNCHRONIZE = &H100000
Public Const KEY_NOTIFY = &H10
Public Const READ_CONTROL = &H20000
Public Const STANDARD_RIGHTS_READ = &H20000
Public Const KEY_QUERY_VALUE = &H1
Public Const KEY_ENUMERATE_SUB_KEYS = &H8
Public Const KEY_SET_VALUE = &H2
Public Const ERROR_FILE_NOT_FOUND = 2
Public Const SUCCESS = 0
Public Const REG_OPTION_NON_VOLATILE = 0
Public Const REG_SZ = 1
Public Const HKEY_LOCAL_MACHINE = &H80000002
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