SPI_SETDISABLEOVERLAPPEDCONTENT - windows

Question

I have function
function bgSetDisableOverlappedContent(CAA: BOOL; var ErrorCode: DWORD; ErrorText: string): Boolean;
begin
errorCode := ERROR_SUCCESS;
ErrorText := '';
if not GetOSVersion >= 60 then
Exit;
Result := SystemParametersInfo(SPI_SETDISABLEOVERLAPPEDCONTENT, 0, #CAA, 0);
if not Result then
begin
ErrorCode := GetLastError;
ErrorText := GetErrorText(ErrorCode);
end;
end;
and call it exactly
procedure TForm1.Button3Click(Sender: TObject);
var
CAA: BOOL;
OS: TUsableInOS;
ErrorCode: DWORD;
ErrorText: string;
begin
CAA := False;
if bgSetDisableOverlappedContent(CAA, ErrorCode, ErrorText) then
ShowMessage('Success');
end;
But, when I inspect again with next code
function bgGetDisableOverlappedContent(var CAA: BOOL; OS: TUsableInOS; ErrorCode: DWORD; ErrorText: string): Boolean;
begin
errorCode := ERROR_SUCCESS;
ErrorText := '';
os := tosVistaUp;
if not GetOSVersion >= 60 then
Exit;
Result := SystemParametersInfo(SPI_GETDISABLEOVERLAPPEDCONTENT, 0, #CAA, 0);
if not Result then
begin
ErrorCode := GetLastError;
ErrorText := GetErrorText(ErrorCode);
end;
end;
function GetOSVersion: Integer;
var
OSVersionInfo : TOSVersionInfo;
begin
Result:= 0;
FillChar(OsVersionInfo, Sizeof(OsVersionInfo), 0);
OSVersionInfo.dwOSVersionInfoSize := SizeOf(OSVersionInfo);
if GetVersionEx(OSVersionInfo) then
begin
if OSVersionInfo.dwPlatformId = VER_PLATFORM_WIN32_NT then
begin
if (OsVersionInfo.dwMajorVersion = 5) and ((OsVersionInfo.dwMinorVersion = 0)) then
Result:= 50; //2000
if (OsVersionInfo.dwMajorVersion = 5) and ((OsVersionInfo.dwMinorVersion = 1)) then
Result:= 51; //XP
if (OsVersionInfo.dwMajorVersion = 5) and ((OsVersionInfo.dwMinorVersion = 2)) then
Result:= 52; //2003, 2003 R2
if (OsVersionInfo.dwMajorVersion = 6) and ((OsVersionInfo.dwMinorVersion = 0)) then
Result:= 60; //Vista, Windows Server 2008
if (OsVersionInfo.dwMajorVersion = 6) and ((OsVersionInfo.dwMinorVersion = 1)) then
Result:= 61; //Server 2008 R2, 7
end;
end;
end;
result for CAA is again True, even I exactly set CAA := False;
I am working on Win 7. and Result of Result := SystemParametersInfo(SPI_SETDISABLEOVERLAPPEDCONTENT, 0, #CAA, 0); is True, but SPI_GETDISABLEOVERLAPPEDCONTENT returns True for CAA, even in step before it exactly was set as False.
procedure TForm1.Button3Click(Sender: TObject);
var
CAA: BOOL;
OS: TUsableInOS;
ErrorCode: DWORD;
ErrorText: string;
Res: Bool;
begin
CAA := False;
{ if bgSetDisableOverlappedContent(CAA, ErrorCode, ErrorText) then
ShowMessage('Success'); }
Res := SystemParametersInfo(SPI_SETDISABLEOVERLAPPEDCONTENT,
0,
#CAA,
0);
Res := SystemParametersInfo(SPI_GETDISABLEOVERLAPPEDCONTENT,
0,
#CAA,
0);
if Caa then
ShowMessage('True')
else
ShowMessage('False');
end;
CAA is True.
Do you have any idea?
Thanks in advance
Bojan

Answer 1

The main problem is that when passing SPI_SETDISABLEOVERLAPPEDCONTENT you are meant to pass a BOOL variable, but you are passing a pointer to a BOOL. The documentation says:
The pvParam parameter is a BOOL variable. Set pvParam to TRUE to disable overlapped content, or FALSE to enable overlapped content.
Which means that your code to set the property needs to be like this:
SystemParametersInfo(SPI_SETDISABLEOVERLAPPEDCONTENT, 0, Pointer(CAA), 0)
Your GetOSVersion is a disaster. Sorry to sound harsh! It returns 0 for Windows 8 and later. And your code has problems with operator precedence. You write:
if not GetOSVersion >= 60 then
and operator precedence means that is interpreted as
if (not GetOSVersion) >= 60 then
Since GetOSVersion returns a signed value, (not GetOSVersion) >= 60 evaluates to False irrespective of windows version. That's because not GetOSVersion is always <= 0.
You want logical negation rather than bitwise negation. So you should write
if not (GetOSVersion >= 60) then
or equivalently
if GetOSVersion < 60 then
In reality there is a built in function to do this. It's called CheckWin32Version. Call it like this:
if not CheckWin32Version(6, 0) then
exit;
The rest of your function is a bit of a mess though. You pass ErrorText by value and then assign to it. Presumably you are intending the caller to receive that value. Which won't happen unless you passed by var.
Personally I'd write your procedure like this:
procedure bgSetDisableOverlappedContent(CAA: BOOL);
begin
if CheckWin32Version(6, 0) then
if not SystemParametersInfo(SPI_SETDISABLEOVERLAPPEDCONTENT, 0, Pointer(CAA), 0) then
RaiseLastOSError;
end;
I think it's better to convert an error in SystemParametersInfo to an exception since it's an exceptional circumstance. I defy you to actually generate a failure of that call to SystemParametersInfo. In which case there's no point building an error code returning mechanism for something that simply will not happen. Check for errors and convert to a runtime exception. This makes the calling code so much simpler.
Your button click handler can be much simpler:
procedure TForm1.Button3Click(Sender: TObject);
begin
bgSetDisableOverlappedContent(False);
end;
And the getter function is also much more complex than necessary. I'd have it like this:
function bgGetDisableOverlappedContent: Boolean;
var
CAA: BOOL;
begin
if not CheckWin32Version(6, 0) then
begin
Result := False;//or True, I don't know, you decide
exit;
end;
if not SystemParametersInfo(SPI_GETDISABLEOVERLAPPEDCONTENT, 0, #CAA, 0) then
RaiseLastOSError;
Result := CAA;
end;