Return an array after a completion block has finished

问题

I have the following function

- (NSArray*) calendarMonthView:(TKCalendarMonthView*)monthView marksFromDate:(NSDate*)startDate toDate:(NSDate*)lastDate{
    AppDelegate* appDelegate = [UIApplication sharedApplication].delegate;
    _currentStart = startDate;
    _currentEnd = lastDate;

    if(appDelegate.internetActive){
        Webservice *web = [[Webservice alloc]init];
        [web fetchAppointmentsOnCompletionFor:startDate andEnd:lastDate OnCompletion:^(BOOL finished) {
            if(finished){
                [self generateRandomDataForStartDate:startDate endDate:lastDate];
                 // NOW return the self.dataArray
            }
        }];
    }
    return self.dataArray; 
}

I can't figure out how I can return the self.dataArray when the completionblock has finished. Because my self.dataArray is filled inside the method generateRandomDataForStartDate:startDate . So at the moment the function always returns an empty array.

Thanks in advandce

回答1:

You should pass the completion handler block inside the argument. Make the return type to void.

Caller object will write below code:

[calenderView calendarMonthView:monthView marksFromDate:startDate toDate:lastDate completionHandler:^(NSarray *dataArray){
//Process data array over here
}];

- (void) calendarMonthView:(TKCalendarMonthView*)monthView marksFromDate:(NSDate*)startDate toDate:(NSDate*)lastDate completionHandler:(void (^)(NSArray*))completionBlock{
    AppDelegate* appDelegate = [UIApplication sharedApplication].delegate;
    _currentStart = startDate;
    _currentEnd = lastDate;

    if(appDelegate.internetActive){
        Webservice *web = [[Webservice alloc]init];
        [web fetchAppointmentsOnCompletionFor:startDate andEnd:lastDate OnCompletion:^(BOOL finished) {
            if(finished){
                [self generateRandomDataForStartDate:startDate endDate:lastDate];
                 completionBlock(self.dataArray);
            }
        }];
    }
    completionBlock(self.dataArray);
}

In the caller code handle completion block with response array received as argumnet.

回答2:

You don't need to return an array from this method, As you mentioned that your dataArray is filling under the generateRandomDataForStartDate:startDate Method, So you can process the filled array from that method, So your code will be,

    - (void) calendarMonthView:(TKCalendarMonthView*)monthView marksFromDate:(NSDate*)startDate toDate:(NSDate*)lastDate{
    AppDelegate* appDelegate = [UIApplication sharedApplication].delegate;
   _currentStart = startDate;
   _currentEnd = lastDate;

   if(appDelegate.internetActive){
    Webservice *web = [[Webservice alloc]init];
    [web fetchAppointmentsOnCompletionFor:startDate andEnd:lastDate OnCompletion:^(BOOL finished) {
        if(finished){
            [self generateRandomDataForStartDate:startDate endDate:lastDate];
             // NOW return the self.dataArray
        }
    }];
}
}

And your method , which is populating the array, should return the modified array,

    -(NSArray *)generateRandomDataForStartDate:(NSString *)startDate endDate:(NSString *)endDate {
    // Your code here to populate and filling array
      return self.dataArray;
    }

来源：https://stackoverflow.com/questions/20947755/return-an-array-after-a-completion-block-has-finished