How to check if the system master volume is mute or unmute?

Question

I\'m using this code to mute/unmute system master volume:

const
  APPCOMMAND_VOLUME_MUTE = $80000;
  WM_APPCOMMAND = $319;

procedure TForm1.Button1Click(Sen         


        

Answer 1

The GetMute method's parameter should be BOOL rather than Boolean. Likewise for SetMute. –

Well, that is to say.. Yes and no.. Yes A Delphi BOOL (actually a LongBool) can store a C-BOOL. No, because it can't be used to write to a C-BOOL property. You will get a 0x80070057 = "Wrong Parameter" result.

The simple reason is that In Delphi True means "everything but 0" and represents -1. A C-BOOL True, however represents 1 and only 1.

So, using a LongBool doesn't work and you should use a workaround using an INT, LongInt, Integer or your own proper defined "BOOL" to avoid "Wrong Parameter" results.

Here an example (that works in Delphi XE7 and tested with SDK version 10.0.10586.15:

// Workaround for BOOL
type TcBOOL = (cFalse = Integer(0),
               cTrue = Integer(1));

// IAudioEndpointVolume
function SetMute(bMute: BOOL; pguidEventContext: PGUID): HRESULT; stdcall;
function GetMute(out pbMute: BOOL): HRESULT; stdcall;


// Client functions
function TMfpMixer.GetMute(): TcBOOL;
var
  hr: HResult;
  Res: BOOL;

begin
  hr:= FAudioEndpoint.GetMute(Res);

  if FAILED(hr) then
    OleCheck(hr);

  Result:= TcBOOL(Res);
end;

//
procedure TMfpMixer.SetMute(Value: TcBOOL);
var
  hr: HResult;

begin
  // This is a workaround on the Delphi BOOL issue. 
  hr:= FAudioEndpoint.SetMute(BOOL(Value),
                              Nil);
  OleCheck(hr);
end;