Question

Delphi 动态调用Dll，释放时为什么总报错

procedure TForm1.Button2Click(Sender: TObject);
type
tfun = function(instr: PansiChar; outstr: PansiChar; len: Integer)
: Integer; stdcall;
var
dll: THandle;
DeviceQuaryCommand: tfun;
pinstr, poutstr: PansiChar;
begin
dll := LoadLibrary('RelayControlCtl.DLL');
try
if dll <> 0 then
begin
@DeviceQuaryCommand := GetProcAddress(dll, 'DeviceQuaryCommand');
if @DeviceQuaryCommand <> nil then
begin
pinstr := ('R1:ON');
poutstr := GetMemory(10);
ZeroMemory(poutstr, 10);
DeviceQuaryCommand(pinstr, poutstr, 10);
MemoOutput.Text := (poutstr);
freememory(poutstr);
end;
end;
finally
FreeLibrary(dll);//这里报错，不知道为什么
end;
end;

Answer 1

首先，if dll <> 0 then应该放到try的前面，其次，DLL可能用到了COM，如果是这样，就要用

begin
CoInitialize(nil);
try

finally
CoUninitialize;
end;
end;
来初始化COM运行环境和做运行环境的善后处理。