Clipboard access routines which use only API functions (Views: 30)
Problem/Question/Abstract: Clipboard access routines which use only API functions Answer: This unit provides clipboard access routines that do not rely on the VCL Clipbrd unit. That unit drags in Dialogs and Forms and a major part of the VCL as a consequence, not appropriate for simple console or non-form programs. This unit uses only API routines, the only VCL units used are Classes (for exceptions and streams) and SysUtils. {Clipboard access routines using only API functions Author: Dr. Peter Below Version 1.0 created 5 Juli 2000 Current revision 1.0 Last modified: 5 Juli 2000} unit APIClipboard; interface uses Windows, Classes; procedure StringToClipboard(const S: string); function ClipboardAsString: string; procedure CopyDataToClipboard(fmt: DWORD; const data; datasize: Integer; emptyClipboardFirst: Boolean = true); procedure CopyDataFromClipboard(fmt: DWORD; S: TStream); function ClipboardHasFormat(fmt: DWORD): Boolean; implementation uses Sysutils; type {This is an internal exception class used by the unit=APIClipboard } EclipboardError = class(Exception) public constructor Create(const msg: string); end; resourcestring eSystemOutOfMemory = 'could not allocate memory for clipboard data.'; eLockfailed = 'could not lock global memory handle.'; eSetDataFailed = 'could not copy data block to clipboard.'; eCannotOpenClipboard = 'could not open the clipboard.'; eErrorTemplate = 'APIClipboard: %s'#13#10 + 'System error code: %d'#13#10 + 'System error message: %s'; {EClipboardError.Create - Creates a new EclipboardError object Param msg is the string to embed into the error message Precondition: none Postcondition: none Description: Composes an error message that contains the passed message and the API error code and matching error message. The CreateFmt constructor inherited from the basic Exception class is used to do the work. Created 5.7.2000 by P. Below} constructor EClipboardError.Create(const msg: string); begin CreateFmt(eErrorTemplate, [msg, GetLastError, SysErrorMessage(GetLastError)]); end; {DataToClipboard - Copies a block of memory to the clipboard in a given format Param fmt is the clipboard format to use Param data is an untyped const parameter that addresses the data to copy Param datasize is the size of the data, in bytes Precondition: The clipboard is already open. If not an EClipboardError will result. This precondition cannot be asserted, unfortunately. Postcondition: Any previously exisiting data of this format will have been replaced by the new data, unless datasize was 0 or we run into an exception. In this case the clipboard will be unchanged. Description: Uses API methods to allocate and lock a global memory block of approproate size, copies the data to it and submits the block to the clipboard. Any error on the way will raise an EClipboardError exception. Created 5.7.2000 by P. Below} procedure DataToClipboard(fmt: DWORD; const data; datasize: Integer); var hMem: THandle; pMem: Pointer; begin if datasize <= 0 then Exit; hMem := GlobalAlloc(GMEM_MOVEABLE or GMEM_SHARE or GMEM_ZEROINIT, datasize); if hmem = 0 then raise EclipboardError.Create(eSystemOutOfMemory); pMem := GlobalLock(hMem); if pMem = nil then begin GlobalFree(hMem); raise EclipboardError.Create(eLockFailed); end; Move(data, pMem^, datasize); GlobalUnlock(hMem); if SetClipboardData(fmt, hMem) = 0 then raise EClipboarderror(eSetDataFailed); {Note: API docs are unclear as to whether the memory block has to be freed in case of failure. Since failure is unlikely here lets blithly ignore this issue for now.} end; {DataFromClipboard - Copies data from the clipboard into a stream Param fmt is the clipboard format to look for Param S is the stream to copy to precondition: S <> nil postcondition: If data was copied the streams position will have moved Description: Tries to get a memory block for the requested clipboard format. Nothing further is done if this fails (because the format is not available or the clipboard is not open, we treat neither as error here), otherwise the memory handle is locked and the data copied into the stream. Note that we cannot determine the actual size of the data originally copied to the clipboard, only the allocated size of the memory block! Since GlobalAlloc works with a granularity of 32 bytes the block may be larger than required for the data and thus the stream may contain some spurious bytes at the end. There is no guarantee that these bytes will be 0. If the memory handle obtained from the clipboard cannot be locked we raise an (see class=EClipboardError) exception. Created 5.7.2000 by P. Below} procedure DataFromClipboard(fmt: DWORD; S: TStream); var hMem: THandle; pMem: Pointer; datasize: DWORD; begin Assert(Assigned(S)); hMem := GetClipboardData(fmt); if hMem <> 0 then begin datasize := GlobalSize(hMem); if datasize > 0 then begin pMem := GlobalLock(hMem); if pMem = nil then raise EclipboardError.Create(eLockFailed); try S.WriteBuffer(pMem^, datasize); finally GlobalUnlock(hMem); end; end; end; end; {CopyDataToClipboard - Copies a block of memory to the clipboard in a given format Param fmt is the clipboard format to use Param data is an untyped const parameter that addresses the data to copy Param datasize is the size of the data, in bytes Param emptyClipboardFirst determines if the clipboard should be emptied, true by default Precondition: The clipboard must not be open already Postcondition: If emptyClipboardFirst is true all prior data will be cleared from the clipboard, even if datasize is <= 0. The clipboard is closed again. Description: Tries to open the clipboard, empties it if required and then tries to copy the passed data to the clipboard. This operation is a NOP if datasize <= 0. If the clipboard cannot be opened a (see class=EClipboardError) is raised. Created 5.7.2000 by P. Below} procedure CopyDataToClipboard(fmt: DWORD; const data; datasize: Integer; emptyClipboardFirst: Boolean = true); begin if OpenClipboard(0) then try if emptyClipboardFirst then EmptyClipboard; DataToClipboard(fmt, data, datasize); finally CloseClipboard; end else raise EclipboardError.Create(eCannotOpenClipboard); end; {StringToClipboard - Copies a string to clipboard in CF_TEXT clipboard format Param S is the string to copy, it may be empty. Precondition: The clipboard must not be open already. Postcondition: Any prior clipboard content will be cleared, but only if S was not empty. The clipboard is closed again. Description: Hands the brunt of the work off to (See routine=CopyDataToClipboard), but only if S was not empty. Otherwise nothing is done at all. Created 5.7.2000 by P. Below} procedure StringToClipboard(const S: string); begin if Length(S) > 0 then CopyDataToClipboard(CF_TEXT, S[1], Length(S) + 1); end; {CopyDataFromClipboard - Copies data from the clipboard into a stream Param fmt is the clipboard format to look for Param S is the stream to copy to Precondition: S <> nil The clipboard must not be open already. Postcondition: If data was copied the streams position will have moved. The clipboard is closed again. Description: Tries to open the clipboard, and then tries to copy the data to the passed stream. This operation is a NOP if the clipboard does not contain data in the requested format. If the clipboard cannot be opened a (see class=EClipboardError) is raised. Created 5.7.2000 by P. Below} procedure CopyDataFromClipboard(fmt: DWORD; S: TStream); begin Assert(Assigned(S)); if OpenClipboard(0) then try DataFromClipboard(fmt, S); finally CloseClipboard; end else raise EclipboardError.Create(eCannotOpenClipboard); end; {ClipboardAsString - Returns any text contained on the clipboard. Returns the clipboards content if it contained something in CF_TEXT format, or an empty string. Precondition: The clipboard must not be already open Postcondition: The clipboard is closed. Description: If the clipboard contains data in CF_TEXT format it is copied to a temp memory stream, zero-terminated for good measure and copied into the result string. Created 5.7.2000 by P. Below} function ClipboardAsString: string; const nullchar: Char = #0; var ms: TMemoryStream; begin if not IsClipboardFormatAvailable(CF_TEXT) then Result := EmptyStr else begin ms := TMemoryStream.Create; try CopyDataFromClipboard(CF_TEXT, ms); ms.Seek(0, soFromEnd); ms.WriteBuffer(nullChar, Sizeof(nullchar)); Result := Pchar(ms.Memory); finally ms.Free; end; end; end; {ClipboardHasFormat - Checks if the clipboard contains data in the specified format Param fmt is the format to check for. Returns true if the clipboard contains data in this format, false otherwise Precondition: none Postcondition: none Description: This is a simple wrapper around an API function. Created 5.7.2000 by P. Below} function ClipboardHasFormat(fmt: DWORD): Boolean; begin Result := IsClipboardFormatAvailable(fmt); end; end. |