HRESULT Next( ULONG celt, LPOLESTR * rgelt, ULONG * pceltFetched );In Delphi 2005 the declaration would be:
function Next(celt: Longint; [out, MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPWStr, SizeParamIndex = 0)] rgelt: array of string; out pceltFetched: Longint ): Integer;Advanced techniques When working with safearrays, the marshal layer automatically converts (for example) an array of bytes into the corresponding safearray type. The marshal layer is very sensitive to type mismatches when converting safearrays. If the type of the safearray does not exactly match the type of the managed array, an exception is thrown. Some of the Win32 safearray API’s do not set the type of the safearray correctly when the array is created, which will lead to a type mismatch in the marshal layer when used from .NET. The solutions are to either ensure that the safearray is created correctly, or to bypass the marshal layer’s automatic conversion. The latter choice may be risky (but could be the only alternative if you don’t have the ability to change the COM server that is providing the data). Consider the following declaration:
function AS_GetRecords(const ProviderName: WideString; Count: Integer; out RecsOut: Integer; Options: Integer; const CommandText: WideString; var Params: OleVariant; var OwnerData: OleVariant): OleVariant;If the return value is known to always be a safearray (that doesn’t describe its type correctly) wrapped in a variant, we can change the declaration to the following:
type
TSafeByteArrayData = packed record
VType: Word;
Reserved1: Word;
Reserved2: Word;
Reserved3: Word;
VArray: IntPtr; { This is a pointer to the actual SafeArray }
end;
function AS_GetRecords(const ProviderName: WideString; Count: Integer;
out RecsOut: Integer; Options: Integer; const CommandText: WideString;
var Params: OleVariant; var OwnerData: OleVariant): TSafeByteArrayData;
Knowing that an OleVariant is a record, the TSafeByteArrayData record can be extracted from Delphi 7’s TVarData (equivalent to the case where the data type is varArray). The record will provide access to the raw pointer to the safearray, from which data can be extracted. By using a structure instead of an OleVariant, the marshal layer will not try to interpret the type of data in the array. You will however be burdened with extracting the data from the actual safearray. Special cases Although it is preferred to use Activator.CreateInstance when creating an instance, it is not fully compatible with CoCreateInstanceEx. When working with remote servers, CreateInstance will always try to invoke the server locally, before attempting to invoke the server on the remote machine. Currently the only known work-around is to use CoCreateInstanceEx. Since inheritance isn’t supported, a descendant interface needs to declare the ancestor’s methods. Below is the IAutoComplete2 interface, which extends IAutoComplete. [ComImport, GuidAttribute(''''EAC04BC0-3791-11d2-BB95-0060977B464C''''), InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
IAutoComplete2 = interface(IAutoComplete)
// IAutoComplete methods
function Init(hwndEdit: HWND; punkACL: IEnumString;
pwszRegKeyPath: IntPtr; pwszQuickComplete: IntPtr): HRESULT;
function Enable(fEnable: BOOL): HRESULT;
//
function SetOptions(dwFlag: DWORD): HRESULT;
function GetOptions(var dwFlag: DWORD): HRESULT;
end;
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