怎么用DELPHI实现后台按键

如果你用定时器，那么和最小化无关，本身还是应该支持的。
SendMessage是可以的，但是你要针对对应的窗口去发送消息。
参考下面的代码：
PostKeyExHWND第一个参数为WebBrowser的控件句柄。

procedure PostKeyEx32(key: Word; const shift: TShiftState; specialkey: Boolean);
{************************************************************
* Procedure PostKeyEx32
*
* Parameters:
* key : virtual keycode of the key to send. For printable
* keys this is simply the ANSI code (Ord(character)).
* shift : state of the modifier keys. This is a set, so you
* can set several of these keys (shift, control, alt,
* mouse buttons) in tandem. The TShiftState type is
* declared in the Classes Unit.
* specialkey: normally this should be False. Set it to True to
* specify a key on the numeric keypad, for example.
* Description:
* Uses keybd_event to manufacture a series of key events matching
* the passed parameters. The events go to the control with focus.
* Note that for characters key is always the upper-case version of
* the character. Sending without any modifier keys will result in
* a lower-case character, sending it with [ssShift] will result
* in an upper-case character!
// Code by P. Below
************************************************************}
type
TShiftKeyInfo = record
shift: Byte;
vkey: Byte;
end;
byteset = set of 0..7;
const
shiftkeys: array [1..3] of TShiftKeyInfo =
((shift: Ord(ssCtrl); vkey: VK_CONTROL),
(shift: Ord(ssShift); vkey: VK_SHIFT),
(shift: Ord(ssAlt); vkey: VK_MENU));
var
flag: DWORD;
bShift: ByteSet absolute shift;
i: Integer;
begin
for i := 1 to 3 do
begin
if shiftkeys[i].shift in bShift then
keybd_event(shiftkeys[i].vkey, MapVirtualKey(shiftkeys[i].vkey, 0), 0, 0);
end; { For }
if specialkey then
flag := KEYEVENTF_EXTENDEDKEY
else
flag := 0;

keybd_event(key, MapvirtualKey(key, 0), flag, 0);
flag := flag or KEYEVENTF_KEYUP;
keybd_event(key, MapvirtualKey(key, 0), flag, 0);

for i := 3 downto 1 do
begin
if shiftkeys[i].shift in bShift then
keybd_event(shiftkeys[i].vkey, MapVirtualKey(shiftkeys[i].vkey, 0),
KEYEVENTF_KEYUP, 0);
end; { For }
end; { PostKeyEx32 }

procedure TForm1.Button1Click(Sender: TObject);
begin
//Pressing the Left Windows Key
PostKeyEx32(VK_LWIN, [], False);

//Pressing the letter D
PostKeyEx32(Ord('D'), [], False);

//Pressing Ctrl-Alt-C
PostKeyEx32(Ord('C'), [ssctrl, ssAlt], False);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
{or you can also try this simple example to send any
amount of keystrokes at the same time. }

{Pressing the A Key and showing it in the Edit1.Text}

Edit1.SetFocus;
keybd_event(VK_SHIFT, 0, 0, 0);
keybd_event(Ord('A'), 0, 0, 0);
keybd_event(VK_SHIFT, 0, KEYEVENTF_KEYUP, 0);

{Presses the Left Window Key and starts the Run}
keybd_event(VK_LWIN, 0, 0, 0);
keybd_event(Ord('R'), 0, 0, 0);
keybd_event(VK_LWIN, 0, KEYEVENTF_KEYUP, 0);
end;

{***********************************************************}

procedure PostKeyExHWND(hWindow: HWnd; key: Word; const shift: TShiftState;
specialkey: Boolean);
{************************************************************
* Procedure PostKeyEx
*
* Parameters:
* hWindow: target window to be send the keystroke
* key : virtual keycode of the key to send. For printable
* keys this is simply the ANSI code (Ord(character)).
* shift : state of the modifier keys. This is a set, so you
* can set several of these keys (shift, control, alt,
* mouse buttons) in tandem. The TShiftState type is
* declared in the Classes Unit.
* specialkey: normally this should be False. Set it to True to
* specify a key on the numeric keypad, for example.
* If this parameter is true, bit 24 of the lparam for
* the posted WM_KEY* messages will be set.
* Description:
* This procedure sets up Windows key state array to correctly
* reflect the requested pattern of modifier keys and then posts
* a WM_KEYDOWN/WM_KEYUP message pair to the target window. Then
* Application.ProcessMessages is called to process the messages
* before the keyboard state is restored.
* Error Conditions:
* May fail due to lack of memory for the two key state buffers.
* Will raise an exception in this case.
* NOTE:
* Setting the keyboard state will not work across applications
* running in different memory spaces on Win32 unless AttachThreadInput
* is used to connect to the target thread first.
*Created: 02/21/96 16:39:00 by P. Below
************************************************************}
type
TBuffers = array [0..1] of TKeyboardState;
var
pKeyBuffers: ^TBuffers;
lParam: LongInt;
begin
(* check if the target window exists *)
if IsWindow(hWindow) then
begin
(* set local variables to default values *)
pKeyBuffers := nil;
lParam := MakeLong(0, MapVirtualKey(key, 0));

(* modify lparam if special key requested *)
if specialkey then
lParam := lParam or $1000000;

(* allocate space for the key state buffers *)
New(pKeyBuffers);
try
(* Fill buffer 1 with current state so we can later restore it.
Null out buffer 0 to get a "no key pressed" state. *)
GetKeyboardState(pKeyBuffers^[1]);
FillChar(pKeyBuffers^[0], SizeOf(TKeyboardState), 0);

(* set the requested modifier keys to "down" state in the buffer*)
if ssShift in shift then
pKeyBuffers^[0][VK_SHIFT] := $80;
if ssAlt in shift then
begin
(* Alt needs special treatment since a bit in lparam needs also be set *)
pKeyBuffers^[0][VK_MENU] := $80;
lParam := lParam or $20000000;
end;
if ssCtrl in shift then
pKeyBuffers^[0][VK_CONTROL] := $80;
if ssLeft in shift then
pKeyBuffers^[0][VK_LBUTTON] := $80;
if ssRight in shift then
pKeyBuffers^[0][VK_RBUTTON] := $80;
if ssMiddle in shift then
pKeyBuffers^[0][VK_MBUTTON] := $80;

(* make out new key state array the active key state map *)
SetKeyboardState(pKeyBuffers^[0]);
(* post the key messages *)
if ssAlt in Shift then
begin
PostMessage(hWindow, WM_SYSKEYDOWN, key, lParam);
PostMessage(hWindow, WM_SYSKEYUP, key, lParam or $C0000000);
end
else
begin
PostMessage(hWindow, WM_KEYDOWN, key, lParam);
PostMessage(hWindow, WM_KEYUP, key, lParam or $C0000000);
end;
(* process the messages *)
Application.ProcessMessages;

(* restore the old key state map *)
SetKeyboardState(pKeyBuffers^[1]);
finally
(* free the memory for the key state buffers *)
if pKeyBuffers <> nil then
Dispose(pKeyBuffers);
end; { If }
end;
end; { PostKeyEx }

procedure TForm1.Button1Click(Sender: TObject);
var
targetWnd: HWND;
begin
targetWnd := FindWindow('notepad', nil)
if targetWnd <> 0 then
begin
PostKeyExHWND(targetWnd, Ord('I'), [ssAlt], False);
end;
end;

我建议你搜索“delphi 全局热键”可以找到你需要的内容

比较难搞啊