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The Functions
CEGetSetting and CESaveSetting are similar. For brevity,
I will discuss CEGetSetting here. Both functions are contained in modReg.bas.
Definition and Declarations
Everything in eVB is a variant but the IDE still allows
us to declare variables and parameters as we would in VB6. I have found
that declaring them with their proper types does not affect the application
but does provide IntelliSense support.
Key_Read is created from the constants shown above.
Public Function CEGetSetting(ByRef strError As Variant,
ByVal APPNAME As String, _ ByVal Section As String, ByVal Key As String,
ByRef Setting As String) As Boolean
On Error Resume Next
Dim lngSize As Long
Dim hlngSubKey As Long
Dim lngType As Long
Dim lngResult As Long
Dim Key_Read As Long
Dim SubKey As String
'False until proven true...
CEGetSetting = False
Key_Read = ((STANDARD_RIGHTS_READ Or KEY_QUERY_VALUE Or KEY_ENUMERATE_SUB_KEYS
OrKEY_NOTIFY) And (Not SYNCHRONIZE))
Without an On error goto construct, error handling
in eVB has to be done a little differently. As discussed above I declare
every function with a boolean return value and a (ByRef) error string.
I set the return value false for safety at the top of the routine. If
the routine executes to completion the return value will be set to true.
If an error occurs anywhere in the function the return value will remain
false.
Validate Parameters
The API calls are not at all forgiving. It is important
to validate the incoming parameters before making the API calls. If you
thought debugging API calls in VB 6 was no fun just wait
'Fill the "Setting" parameter with 256 chr(0)'s
lngSize = 256
Setting = String(lngSize, 0)
SubKey = APPNAME & "\" & Section
The SubKey is the concatenation of the application
name and section. Recall that in our example the application name is SOFTWARE\pktSoft\TTDS
and the section is Settings so the SubKey becomes SOFTWARE\pktSoft\TTDS\
Settings.
Open the Registry
We are ready to make the first API call. We want to
try and open the key under HKEY_LOCAL_MACHINE. If we are able to open
the key then lngResult will be 0 and hlngSubKey will be set.
'Open the registry key and
find a handle to the sub key
'It is always under HKEY_LOCAL_MACHINE
'Return hlngSubKey, lngResult indicates success or failure
lngResult = RegOpenKeyEx(HKEY_LOCAL_MACHINE,
SubKey, 0, Key_Read, hlngSubKey)
If (lngResult <> ERROR_SUCCESS)
Then
strError = "CEGetSetting: Unable to open the registry sub-key
'" & SubKey & "'."
Exit Function
End If
Try to Read the Key and get the Setting
If we made it this far then we should be able to open
the Key and read the Setting. The function uses hlngSubKey from the previous
call.
'Try to read the value of the item
'Pass in hlngSubKey and the Key we are looking for.
'Setting is 256 chr(0) on the way in (Byref).
'Return lngType, strItemValue, lngSize
lngResult = RegQueryValueEx(hlngSubKey, Key, 0, lngType, Setting, lngSize)
If (lngResult = ERROR_SUCCESS) And (lngType = 1) Then
'OK - the Setting came back but it is 256 chars long, padded
with chr(0).
Setting = Left(Setting, lngSize - 1)
Else
'Error...
'Close the registry before we exit
lngResult = RegCloseKey(hlngSubKey)
lngResult = RegCloseKey(HKEY_LOCAL_MACHINE)
strError = "CEGetSetting: Unable to read the registry value
for '" & Key & "'. (" & lngResult & ")."
Exit Function
End If
Clean Up
If we got this far then we have successfully retrieved
the setting. We can close the registry and set the CEGetSetting return
value to True.
'All is well if we got this far. Close the keys.
lngResult = RegCloseKey(hlngSubKey)
lngResult = RegCloseKey(HKEY_LOCAL_MACHINE)
strError = ""
CEGetSetting = True
Sample Calls
I normally read registry keys when the application
loads (in the form_load event) and save registry settings when a form
or the application closes. This code executes so fast that you can save
settings in text_change events if needed. Assume we want to retrieve the
name of the SQL Server 2000/CE database name from the registry when the
application is first run.
APPNAME is globally declared as follows:
Public Const APPNAME = "SOFTWARE\pktSoft\TTDS"
The following code is from the form_load event:
Dim bRes As Boolean
Dim strError As String
Dim strDB as String
bRes = CEGetSetting(strError,
APPNAME, "Settings", _
"DatabasePath", strDB)
If bRes = False Then
MsgBox strError, vbExclamation
Else
txtLocalDatabase.Text = strDB
End If
If the setting is found then the text control in the
application is set. When this application closes the DatabasePath is written
back to the registry (in case the user changed it). Note that we can pass
the control text property as a function parameter. The code (in the Form_OKClick
event) is:
Dim bRes As Boolean
Dim strError As String
'Save the database path
bRes = CESaveSetting(strError, APPNAME, "Settings", _
"DatabasePath", txtLocalDatabase.Text)
If bRes = False Then
MsgBox strError, vbExclamation
End If
Summary
As VB 6 developers we have come to rely on the Windows
API to implement functionality not found in the base language. Windows
CE offers many familiar API functions and eVB can use them as easily as
VB 6 uses the Windows API. Convenient access to the registry is something
I rely on in every VB 6 application I write and porting my existing code
to eVB was relatively easy.
[1] HKEY_LOCAL_MACHINE
is added in code
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