What's a simple way of programmatically simulating user input?

I have a dialog that pops up as result of an error condition. I want the dialog to remain open for at least 开发者_高级运维30 seconds, and close 30 seconds after the last user input (mouse or keyboard) is received.

I can implement this by checking the value returned by GetLastInputInfo and closing the dialog when this is more than 30 seconds ago, but if the dialog pops up when the user hasn't been at the mouse or keyboard for 30 seconds, the GetLastInputInfo test passes immediately, and the dialog closes again immediately. I could do this with another timer, but I figure it would be much simpler to simulate the mouse being moved a bit, or issuing a (harmless) keypress, just before the dialog opens. It would also have the advantage presumably of kicking the system out of screensaver.

What's the simplest 1-line Delphi code fragment to achieve this?

the most simple is using the keybd_event function (one line of code)

keybd_event(Ord('A'), 0, 0, 0);

Also you can use the SendInput function but requires more than one line :)

Var
  pInputs : TInput;
begin
    pInputs.Itype := INPUT_KEYBOARD;
    pInputs.ki.wVk := Ord('A');
    pInputs.ki.dwFlags := KEYEVENTF_KEYUP;
    SendInput(1, pInputs, SizeOf(pInputs));
end;

Input multiple byte characters with keybd_event:

procedure InsertText(text:string);
var i:integer;
    j:integer;
    ch:byte;
    str:string;
begin
  i:=1;
  while i<=Length(text) do
  begin
    ch:=byte(text[i]);
    if Windows.IsDBCSLeadByte(ch) then
       begin
         Inc(i);
         str:=inttostr(MakeWord(byte(text[i]), ch));
         keybd_event(VK_MENU, MapVirtualKey(VK_MENU, 0), 0, 0);
         j:=1;
         while j<=Length(str) do
         begin
               keybd_event(96+strtoint(str[j]), MapVirtualKey(96+strtoint(str[j]), 0), 0, 0);
               keybd_event(96+strtoint(str[j]), MapVirtualKey(96+strtoint(str[j]), 0), 2, 0);
               j:=j+1;
         end;
         keybd_event(VK_MENU, MapVirtualKey(VK_MENU, 0), KEYEVENTF_KEYUP, 0);
       end
    else begin
           keybd_event(VkKeyScan(text[i]),0,0,0);
           keybd_event(VkKeyScan(text[i]),0,2,0);
         end;
    Inc(i);
  end;
end;

https://github.com/WladiD/SendInputHelper by Mr. Waldemar Derr.

Simple and versatile, choose 2.

Example:

uses
  ..., SendInputHelper;

procedure TForm1.Button1Click(Sender: TObject);
var
  SIH: TSendInputHelper;
begin
  SIH := TSendInputHelper.Create;
  try
    // Start command shell
    SIH.AddShortCut([ssWin], 'r'); // Win+R
    SIH.AddDelay(100);
    SIH.AddText('cmd', True); // Second parameter True means AppendReturn
    SIH.AddDelay(500);

    SIH.AddText('ping google.de', True); // Perform a ping.

    SIH.Flush; // Isn't it easy?
  finally
    SIH.Free;
  end;
end;