如何更改默认打印机

Question

我试图在列出打印机索引的组合框的更改事件中更改默认打印机。我使用“打印机”来获取打印机索引，但实际打印是使用专有打印代码完成的，该代码允许直接打印 pdf 并更轻松地进行页面布局。我试图使用下面的代码来更改默认打印机，然后我的打印代码将打印到该打印机。然而，当执行这行代码时，程序变得无响应，没有任何错误或程序不响应消息：

SendMessage( HWND_BROADCAST, WM_WININICHANGE, 0,LongInt(cs1));

这是完整的函数。

function TMainFrm.SetDefaultPrinter(const PrinterName: string): boolean;
// Printername is bv: '\\MYPRINTER\HP5-k'
var
s2 : string;
dum1 : Pchar;
xx, qq : integer;

const
cs1 : pchar = 'Windows';
cs2 : pchar = 'Device';
cs3 : pchar = 'Devices';
cs4 : pchar = #0;

begin
    xx := 254;
    GetMem( dum1, xx);
    Result := False;
    try
        qq := GetProfileString( cs3, pchar( PrinterName ), #0, dum1, xx);
    if (qq > 0) and (trim( strpas( dum1 )) <> '') then
    begin
        s2 := PrinterName + ',' + strpas( dum1 );
        while GetProfileString( cs1, cs2, cs4, dum1, xx) > 0 do
            WriteProfileString( cs1, cs2, #0);
            WriteProfileString( cs1, cs2, pchar( s2 ));
        case Win32Platform of
        VER_PLATFORM_WIN32_NT :
            SendMessage( HWND_BROADCAST, WM_WININICHANGE, 0,LongInt(cs1));
        VER_PLATFORM_WIN32_WINDOWS :
            SendMessage( HWND_BROADCAST, WM_SETTINGCHANGE, 0,LongInt(cs1));
        end; { case }
        Result := True;
    end;
    finally
        FreeMem( dum1 );
    end;
end;

有人有任何提示或更好的方法来做到这一点吗？

附带说明一下，这不是我的职责。这是我在寻找问题解决方案时捡到的一段代码。

更多信息：

打印作业实际上是正在打印的 PDF

 ShellExecute(Application.Handle, 'print', PChar(sPath), nil, nil, SW_HIDE); 

目标是将默认打印机更改为选定的打印机，以便将 pdf 打印到所需的打印机，然后在退出应用程序时将打印机返回到原始默认值

Answer 1

尝试使用 Win32_Printer WMI 类列出打印机和设置默认打印机< /a> 设置默认打印机的方法。

{$APPTYPE CONSOLE}

uses
  SysUtils,
  ActiveX,
  ComObj,
  Variants;

procedure  ListPrinters;
const
  wbemFlagForwardOnly = $00000020;
var
  FSWbemLocator : OLEVariant;
  FWMIService   : OLEVariant;
  FWbemObjectSet: OLEVariant;
  FWbemObject   : OLEVariant;
  oEnum         : IEnumvariant;
  iValue        : LongWord;
begin;
  FSWbemLocator := CreateOleObject('WbemScripting.SWbemLocator');
  FWMIService   := FSWbemLocator.ConnectServer('localhost', 'root\CIMV2', '', '');
  FWbemObjectSet:= FWMIService.ExecQuery('SELECT DeviceID, Name FROM Win32_Printer','WQL',wbemFlagForwardOnly);
  oEnum         := IUnknown(FWbemObjectSet._NewEnum) as IEnumVariant;
  while oEnum.Next(1, FWbemObject, iValue) = 0 do
  begin
    Writeln(Format('DeviceID %s Name %s',[FWbemObject.DeviceID,FWbemObject.Name]));
    FWbemObject:=Unassigned;
  end;
end;

function  SetDefaultPrinter(const DeviceID:string):boolean;
var
  FSWbemLocator : OLEVariant;
  FWMIService   : OLEVariant;
  FWbemObject   : OLEVariant;
begin;
  FSWbemLocator := CreateOleObject('WbemScripting.SWbemLocator');
  FWMIService   := FSWbemLocator.ConnectServer('localhost', 'root\CIMV2', '', '');
  FWbemObject   := FWMIService.Get(Format('Win32_Printer.DeviceID="%s"',[DeviceID]));
  if not VarIsClear(FWbemObject) then
   Result:=FWbemObject.SetDefaultPrinter()=0
  else
   Result:=false;
end;


begin
 try
    CoInitialize(nil);
    try
      ListPrinters;
      SetDefaultPrinter('HP LaserJet'); //here you must pass the DeviceID of one the printers listed above
    finally
      CoUninitialize;
    end;
 except
    on E:EOleException do
        Writeln(Format('EOleException %s %x', [E.Message,E.ErrorCode]));
    on E:Exception do
        Writeln(E.Classname, ':', E.Message);
 end;
 Writeln('Press Enter to exit');
 Readln;
end.

Answer 2

只需简单浏览一下 此链接，您就会发现您错过了最关键的函数 SetDefaultPrinterA/SetDefaultPrinterW在“winspool.drv”中，

广播消息的设计也是为了对其他正在运行的程序有礼貌，让它们知道某些内容已经更改了默认打印机，即使在上面的文章中，它似乎也没有注意到结果，以便您可以更改对 PostMessage 的调用

Answer 3

我还尝试使用“SendMessage( HWND_BROADCAST, WM_WININICHANGE, 0,LongInt(cs1))”代码块，但我的程序挂起。因此，我尝试简单地将 SetDefaultPrinter 编写为本地函数，然后就不会出现挂起情况。这是适合我的代码。

function SetDefaultPrinter(const PrinterName: string): boolean;
// Printername is bv: '\\MYPRINTER\HP5-k'
var
s2 : string;
dum1 : PChar;
xx, qq : integer;

const
cs1 : pChar = 'Windows';
cs2 : pChar = 'Device';
cs3 : pChar = 'Devices';
cs4 : pChar = #0;

begin
    xx := 254;
    GetMem( dum1, xx);
    Result := False;
    try
            qq := GetProfileString( cs3, pChar( PrinterName ), #0, dum1, xx);
            if (qq > 0) and (trim( strpas( dum1 )) <> '') then
            begin
                s2 := PrinterName + ',' + strpas( dum1 );
                while GetProfileString( cs1, cs2, cs4, dum1, xx) > 0 do
                    WriteProfileString( cs1, cs2, #0);
                    WriteProfileString( cs1, cs2, pChar( s2 ));

                case Win32Platform of
                VER_PLATFORM_WIN32_NT :
                    SendMessage( HWND_BROADCAST, WM_WININICHANGE, 0, LongInt(cs1));
                VER_PLATFORM_WIN32_WINDOWS :
                    SendMessage( HWND_BROADCAST, WM_SETTINGCHANGE, 0,LongInt(cs1));
                end; { case }
                Result := True;
            end;
    finally
        FreeMem( dum1 );
    end;
end;