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Delphi enumeration device usage code_PHP tutorial

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Release： 2016-07-13 10:54:12

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delphi enumeration device usage code

Now delphi (2010, xe) already comes with directx related units (...sourcertlwin).
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//Enumeration function
function directsoundenumerate(
lpdsenumcallback: tdsenumcallback; //Callback function
lpcontext: pointer //User pointer
): hresult; stdcall; //Return error code, if successful, return s_ok(0)

//The prototype of the callback function required by directsoundenumerate:
tdsenumcallback = function(
lpguid: pguid; //Guid of the device
lpcstrdescription: pchar; //Device description
lpcstrmodule: pchar; //Module identification
lpcontext: pointer //User pointer provided by directsoundenumerate
): bool; stdcall; //Returning true means that we want to continue enumeration. If we no longer want to continue searching, return false

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This is the common code:
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unit unit1;

interface

uses
windows, messages, sysutils, variants, classes, graphics, controls, forms,
dialogs, stdctrls;

type
tform1 = class(tform)
Listbox1: tlistbox; //Only one list box is placed on the form
Procedure formcreate(sender: tobject);
end;

var
form1: tform1;

implementation

{$r *.dfm}

uses directsound; //!

function enumcallback(lpguid: pguid; lpcstrdescription, lpcstrmodule: pchar;
lpcontext: pointer): bool; stdcall;
begin
form1.listbox1.items.add(lpcstrdescription);
result := true;
end;

procedure tform1.formcreate(sender: tobject);
begin
directsoundenumerate(enumcallback, nil);
end;

end.

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It is not good to use the form control directly in the callback function. Modify it as follows:
-------------------------------------------------- ----------------------------------

uses directsound;

function enumcallback(lpguid: pguid; lpcstrdescription, lpcstrmodule: pchar;
lpcontext: pointer): bool; stdcall;
begin
tstrings(lpcontext).add(lpcstrdescription);
result := true;
end;

procedure tform1.formcreate(sender: tobject);
begin
directsoundenumerate(enumcallback, listbox1.items);
end;

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Get more information:
-------------------------------------------------- ----------------------------------

uses directsound;

function enumcallback(lpguid: pguid; lpcstrdescription, lpcstrmodule: pchar;
lpcontext: pointer): bool; stdcall;
begin
if lpguid <> nil then tstrings(lpcontext).add(guidtostring(lpguid^));
tstrings(lpcontext).add(lpcstrdescription);
if lpcstrmodule <> nil then tstrings(lpcontext).add(lpcstrmodule);
tstrings(lpcontext).add(emptystr);
result := true;
end;

procedure tform1.formcreate(sender: tobject);
begin
directsoundenumerate(enumcallback, listbox1.items);
end;