ios - How to write block definition using properties? -

i writing class getting image photos library. want 1 single method return selected image library. started writing class named mediabrowser. used block give selected image. confused write block definition. please correct code if going wrong.

in mediabrowser.h

@interface mediabrowser : nsobject  typedef uiimage* (^mediabrowsercompletionhandler)(void);  + (id)sharedinstance; - (bool)startmediabrowserfromviewcontroller:(uiviewcontroller*)controller                           completionhandler:(mediabrowsercompletionhandler)completion; @end 

in mediabrowser.m

@interface mediabrowser () <uiimagepickercontrollerdelegate, uinavigationcontrollerdelegate> @property (nonatomic, strong) mediabrowsercompletionhandler completionhandler; @end  @implementation mediabrowser  static mediabrowser *sharedmediabrowser = nil;  + (id)sharedinstance {     if (nil != sharedmediabrowser) {         return sharedmediabrowser;     }     static dispatch_once_t oncetoken;     dispatch_once(&oncetoken, ^{         sharedmediabrowser = [[mediabrowser alloc] init];     });     return sharedmediabrowser; }  - (bool)startmediabrowserfromviewcontroller:(uiviewcontroller *)controller completionhandler:(mediabrowsercompletionhandler)completion {     self.completionhandler = [completion copy];     if (([uiimagepickercontroller issourcetypeavailable:uiimagepickercontrollersourcetypesavedphotosalbum] == no)         || (controller == nil))         return no;      uiimagepickercontroller *mediaui = [[uiimagepickercontroller alloc] init];     mediaui.sourcetype = uiimagepickercontrollersourcetypesavedphotosalbum;      // displays saved pictures camera roll album.     mediaui.mediatypes = [[nsarray alloc] initwithobjects:(nsstring *)kuttypeimage, nil];      // hides controls moving & scaling pictures, or     // trimming movies. instead show controls, use yes.     mediaui.allowsediting = no;     mediaui.delegate = self;      [controller presentmodalviewcontroller:mediaui animated:yes];     return yes; }  // uiimagepickercontrollerdelegate  - (void)imagepickercontroller:(uiimagepickercontroller *)picker didfinishpickingmediawithinfo:(nsdictionary *)info {     nsstring *mediatype = [info objectforkey: uiimagepickercontrollermediatype];     uiimage *imagetouse;      // handle still image picked photo album     if (cfstringcompare ((cfstringref) mediatype, kuttypeimage, 0) == kcfcompareequalto) {         imagetouse = (uiimage *) [info objectforkey:uiimagepickercontrolleroriginalimage];         // imagetouse         if (self.completionhandler) {             // pass here uiimage             self.completionhandler();         }     }      [picker dismissmodalviewcontrolleranimated:yes]; }  @end 

typedef uiimage* (^mediabrowsercompletionhandler)(void);  @interface mediabrowser : nsobject  @property (nonatomic,copy) mediabrowsercompletionhandler handler;  @end