ios - 从 delphi 调用 objective-c 代码块

Question

我正在尝试在我的 firemonkey 应用程序中进行后台获取。

到目前为止，我的 perfromFetchWithCompletionHandler 被调用并下载了新信息。

当我完成获取并需要调用 completionHandler 代码块时，问题就来了，应用程序挂起并且我没有收到任何异常(我至少可以阅读)

设置:

TBackgroundFetchResultHandlerC = procedure ( AResult : NSUInteger ); cdecl;
.. 
..

procedure performFetchWithCompletionHandler(self : id; _cmd : SEL; application: PUIApplication; handler : TBackgroundFetchResultHandlerC );
..
..

objc_msgSend((UIApp as ILocalObject).GetObjectId,
             sel_getUid('setMinimumBackgroundFetchInterval:'),
             Interval);
class_addMethod( objc_getClass('DelphiAppDelegate') ,
                sel_getUid('application:performFetchWithCompletionHandler:'),
                @performFetchWithCompletionHandler,
                'v@:@?'
  );
..
..

procedure performFetchWithCompletionHandler(self : id; _cmd : SEL; application:         PUIApplication; handler : TBackgroundFetchResultHandlerC );
var t : TThread;
begin
  NSLog3('performFetchWithCompletionHandler:begin');
  Handler(0); <<--Stops here
  //Next line of code never gets called.
  NSLog3(Format('performFetchWithCompletionHandler:done, done',[ FetchResult ]) );
end;

performFetchWithCompletionHandler man page

我已经尝试过函数指针类型的不同声明，但由于它不是一个函数指针，我想这就是它不起作用的原因。

有什么想法吗？

谢谢罗伯特

Answer 1

我找到了一个有效的解决方案:imp_implementationWithBlock

procedure performFetchWithCompletionHandler(self : id; _cmd : SEL; application:    PUIApplication; handler : id );

//将处理程序更改为类型 id(指针)

const
  libobjc = '/usr/lib/libobjc.dylib';

{$IF NOT DECLARED(_PU)}
  const
  {$IFDEF UNDERSCOREIMPORTNAME}
    _PU = '_';
  {$ELSE}
    _PU = '';  
  {$ENDIF}
  {$EXTERNALSYM _PU}
{$ENDIF}

function imp_implementationWithBlock( block :id ) : IMP; cdecl; external libobjc name  _PU + 'imp_implementationWithBlock';
function imp_removeBlock( anImp : IMP ) : integer; cdecl; external libobjc name _PU + 'imp_removeBlock';

//添加了对 libobjc 中 imp_implementationWithBlock 和 imp_removeBlock 的引用

type  IMP = function( self : id; cmd : SEL; Param1 : NSUInteger ) : id; cdecl;

//声明类型 IMP 作为 c 函数对应于 imp_implementationWithBlock 在这种特殊情况下返回的函数指针，带有一个 NSUInteger 参数。

procedure performFetchWithCompletionHandler(self : id; _cmd : SEL; application: PUIApplication; handler : id );
var
  ahandlerimp : IMP;
begin
   .... //Code to perform fetch 
  ahandlerimp := imp_implementationWithBlock( handler ); //Create c function for block
  ahandlerimp(self,_cmd,FetchResult ); //Call c function, _cmd is ignored
  imp_removeBlock(ahandlerimp); //Remove the c function created two lines up
end;