Delphi XE3探索：Winapi.Functiondiscovery （三）

这是Delphi XE3探索：Winapi.Functiondiscovery系列到第三篇文章。

思路分析

Discovery API 不仅仅可以用来枚举设备信息，还可以接收设备通知；例如设备的添加、移除或者设备的属性被修改。为了接收这些设备改变的通知就需要实现 IFunctionDiscoveryNotification接口。AddQueryConstraint 的PROVIDERPNP_QUERYCONSTRAINT_NOTIFICATIONSONLY值用于设置是否仅接收设备通知，最后调用 IFunctionInstanceCollectionQuery.Execute方法。

实现IFunctionDiscoveryNotification 接口

IFunctionDiscoveryNotification 有三个方法用于接收 IFunctionInstanceCollectionQuery.Execute 异步查询的结果。

接口方法

OnError ： Receives errors that occur during asynchronous query processing.
OnEvent ： Receives any add, remove, or update events.
OnUpdate ： Indicates that a function instance has been added, removed, or changed.

IFunctionDiscoveryNotification 接口声明：

IFunctionDiscoveryNotification = interface(IUnknown)
[SID_IFunctionDiscoveryNotification]
  function OnUpdate(enumQueryUpdateAction: QueryUpdateAction; fdqcQueryContext: FDQUERYCONTEXT; pIFunctionInstance: IFunctionInstance): HRESULT; stdcall;
  function OnError(hr: HRESULT; fdqcQueryContext: FDQUERYCONTEXT; pszProvider: PWCHAR): HRESULT; stdcall;
  function OnEvent(dwEventID: DWORD; fdqcQueryContext: FDQUERYCONTEXT; pszProvider: PWCHAR): HRESULT; stdcall;
end;

接口实现代码

type
  TFunctionDiscoveryOnUpdate = procedure(enumQueryUpdateAction: QueryUpdateAction; fdqcQueryContext: FDQUERYCONTEXT;
      pIFunctionInstance: IFunctionInstance) of object;
  TFunctionDiscoveryOnError  = procedure(hr: HRESULT; fdqcQueryContext: FDQUERYCONTEXT; pszProvider: PWCHAR) of object;
  TFunctionDiscoveryOnEvent  = procedure(dwEventID: DWORD; fdqcQueryContext: FDQUERYCONTEXT; pszProvider: PWCHAR) of object;

  TFunctionDiscoveryNotificationSync=class(TInterfacedObject, IFunctionDiscoveryNotification)
  private
    FAction        : QueryUpdateAction;
    FEventAdd      : TEvent;
    FEventRemove   : TEvent;
    FEventChange   : TEvent;
    FOnUpdateEvent : TFunctionDiscoveryOnUpdate;
    FOnErrorEvent  : TFunctionDiscoveryOnError;
    FOnEventEvent  : TFunctionDiscoveryOnEvent;
    function OnUpdate(enumQueryUpdateAction: QueryUpdateAction; fdqcQueryContext: FDQUERYCONTEXT;
      pIFunctionInstance: IFunctionInstance): HRESULT; stdcall;
    function OnError(hr: HRESULT; fdqcQueryContext: FDQUERYCONTEXT; pszProvider: PWCHAR): HRESULT; stdcall;
    function OnEvent(dwEventID: DWORD; fdqcQueryContext: FDQUERYCONTEXT; pszProvider: PWCHAR): HRESULT; stdcall;
  public
    constructor Create;
    destructor Destroy; override;
    function WaitFor(dwTimeout : DWORD; pszCategory: PWCHAR; eAction : QueryUpdateAction) : HRESULT;
    property OnUpdateEvent: TFunctionDiscoveryOnUpdate read FOnUpdateEvent write FOnUpdateEvent;
    property OnErrorEvent : TFunctionDiscoveryOnError read FOnErrorEvent write FOnErrorEvent;
    property OnEventEvent : TFunctionDiscoveryOnEvent read FOnEventEvent write FOnEventEvent;
  end;


{TFunctionDiscoveryNotificationSync}

constructor TFunctionDiscoveryNotificationSync.Create;
begin
  inherited;
  FOnUpdateEvent:=nil;
  //create the  events objects
  FEventAdd    := TEvent.Create(nil, False, False, '', true);
  FEventRemove := TEvent.Create(nil, False, False, '', true);
  FEventChange := TEvent.Create(nil, False, False, '', true);
end;

destructor TFunctionDiscoveryNotificationSync.Destroy;
begin
  //release the event objects
  FEventAdd.Free;
  FEventRemove.Free;
  FEventChange.Free;
  inherited;
end;

function TFunctionDiscoveryNotificationSync.OnError(hr: HRESULT;
  fdqcQueryContext: FDQUERYCONTEXT; pszProvider: PWCHAR): HRESULT;
begin
   //send the error notification if a callback method  was defined
   if @FOnErrorEvent<>nil then
    FOnErrorEvent(hr, fdqcQueryContext, pszProvider);
   Exit(S_OK);
end;

function TFunctionDiscoveryNotificationSync.OnEvent(dwEventID: DWORD;
  fdqcQueryContext: FDQUERYCONTEXT; pszProvider: PWCHAR): HRESULT;
begin
   //send the OnEvent notification if a callback method  was defined
   if @FOnEventEvent<>nil then
    FOnEventEvent(dwEventID, fdqcQueryContext, pszProvider);
   Exit(S_OK);
end;

function TFunctionDiscoveryNotificationSync.OnUpdate(
  enumQueryUpdateAction: QueryUpdateAction; fdqcQueryContext: FDQUERYCONTEXT;
  pIFunctionInstance: IFunctionInstance): HRESULT;
begin

    //signal the event object
    case enumQueryUpdateAction of
      QUA_ADD    : FEventAdd.SetEvent;
      QUA_REMOVE : FEventRemove.SetEvent;
      QUA_CHANGE : FEventChange.SetEvent;
    end;

   //send the OnEvent notification if a callback method  was defined
   if (@FOnUpdateEvent<>nil) and (FAction=enumQueryUpdateAction) then
    FOnUpdateEvent(enumQueryUpdateAction, fdqcQueryContext, pIFunctionInstance);
   Exit(S_OK);
end;

function TFunctionDiscoveryNotificationSync.WaitFor(dwTimeout : DWORD; pszCategory: PWCHAR; eAction : QueryUpdateAction) : HRESULT;
var
 hr : HRESULT;
 LEvent : TEvent;
 LWaitResult : TWaitResult;
 FFunctionDiscovery : IFunctionDiscovery;
 ppIFunctionInstanceCollection: IFunctionInstanceCollection;
 ppIFunctionInstanceCollectionQuery: IFunctionInstanceCollectionQuery;
begin
 FAction:=eAction;
 //reset the event objects
 FEventAdd.ResetEvent;
 FEventRemove.ResetEvent;
 FEventChange.ResetEvent;

 //create a instance to the IFunctionDiscovery
 FFunctionDiscovery := CreateComObject(CLSID_FunctionDiscovery) as IFunctionDiscovery;
 //create a new query passing the current class as callback
 hr := FFunctionDiscovery.CreateInstanceCollectionQuery(FCTN_CATEGORY_PNP, nil, true, Self, nil, ppIFunctionInstanceCollectionQuery);

 //instruct to the query to only receive notifications
 if hr=S_OK then
   hr := ppIFunctionInstanceCollectionQuery.AddQueryConstraint(PROVIDERPNP_QUERYCONSTRAINT_NOTIFICATIONSONLY,'TRUE');

 //execute the query
 if hr=S_OK then
   hr := ppIFunctionInstanceCollectionQuery.Execute(ppIFunctionInstanceCollection);

 if( hr=E_PENDING) then hr := S_OK;

    case eAction of
      QUA_ADD    : LEvent:=FEventAdd;
      QUA_REMOVE : LEvent:=FEventRemove;
      QUA_CHANGE : LEvent:=FEventChange;
      else
      LEvent := nil;
    end;

  if (hr=S_OK) and (LEvent<>nil) then
   LWaitResult:= LEvent.WaitFor(dwTimeout);

 // One device may correspond to multiple function instances
 // This sleep allows the OnUpdate call to output information
 // about each Function Instance.
 // THIS SLEEP IS MERELY FOR DISPLAY PURPOSES
 Sleep(1000);
 Exit(hr);
end;

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