ios - 在单独的线程中循环位置数组

Question

我正在为 iPhone 开发一个应用程序，我正在跟踪用户的当前位置。当 didupdateLocations 委托(delegate)方法实际执行时，我想测试 NSArray 中的位置是否在包含其他位置的预定义数组中，这个数组会随着时间的推移而增长。

我正在这个方法中运行一个 for 循环来测试我自己的位置数组，但我想将它移到一个单独的线程中。因此，如果我自己的具有多个位置的数组增长到很大数量，for 循环不会卡住我的 UI。我试过这样但我得到了不希望的结果。我知道位置跟踪肯定发生在一个单独的线程中。但是，那些 didupdateLocations 在单独的线程上执行。苹果文档对此事不是很清楚。我的最终目标还是与我的数组进行比较而不是锁定 UI。

  - (void)locationManager:(CLLocationManager *)manager
         didUpdateLocations:(NSArray *)thisLocation {

    dispatch_queue_t queue= dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    // get the last object in the array of locations
    CLLocation* location = [thisLocation lastObject];

     dispatch_async(queue, ^{
         [self checkmyArray:location];
     });

}



 -(void)checkmyArray:(CLLocation *)workingLocation{

    NSLog(@"SoundTheAlarm");
     int alarm_on_c = 0;
     NSUInteger tmp_count = [theData.LocationsObjectArray count];
     BOOL alarm;
     NSMutableDictionary * tempObject;
     CLLocationDistance distance = 0.0;


    for (int i = 0; i < tmp_count; i++) {

        tempObject= [theData.LocationsObjectArray objectAtIndex:i];

         thisLoc = [[tempObject objectForKey:@"onoff"] isEqual:@YES];


        if (thisLoc) {


            //check if we are near that location
            double lat = [[tempObject objectForKey:@"latitude"] doubleValue];
            double lon = [[tempObject objectForKey:@"longitude"] doubleValue];

            // goal = [[CLLocation alloc] initWithLatitude:40.097771 longitude:-74.941399];
            goal = [[CLLocation alloc] initWithLatitude:lat longitude:lon];

            // check the destination between current location and goal location - in meters
            distance = [goal distanceFromLocation:workingLocation];

            NSLog(@"distance %f\n", distance);
        }


        // if distance from goal is less than 350 meters
        if (distance <= 350){

                [self scheduleNotification:[tempObject objectForKey:@"name"]];

                // turn off tracking for this location
                [tempObject setObject:@NO forKey:@"onoff"];
                [theData.LocationsObjectArray replaceObjectAtIndex:i withObject:tempObject];

                NSIndexPath *path = [NSIndexPath indexPathForRow:i inSection:0];
                ExtendedSavedCellTableViewCell *cell = (ExtendedSavedCellTableViewCell *)[self.tableView cellForRowAtIndexPath:path];
                cell.switchView.on = NO;

                // save the update to the switch to the database as well
                NSString *lat = [tempObject objectForKey:@"latitude"];

                /*check to determine if the uiswitch is turned off or on.*/

                [self fetchedResultsController:@NO lat:lat index:path];
                [self displayAlertViewForAlarm:[tempObject objectForKey:@"name"]];


}

-(void)displayAlertViewForAlarm:(NSString *)nameOfLocation{

     dispatch_async(dispatch_get_main_queue(), ^(void) {


    UIAlertView *myAlert = [[UIAlertView alloc] initWithTitle:@"Destination reached"
                                                      message:nameOfLocation
                                                     delegate:self
                                            cancelButtonTitle:@"Go Away"
                                            otherButtonTitles:@"Notify", nil];


    [myAlert show];
     });



}

Answer 1

如果可以完全避免的话，在 iOS 中使用线程通常不是一个好主意。在您的情况下，我将实现执行循环的函数，以便在太多次迭代后自动弹出循环，然后安排下一个迭代 block 在事件循环的另一次传递中发生。换句话说，像这样:

- (void) checkLocationsStartingAt:(NSNumber)start
{
    NSInteger s = (start) ? [start intValue] : 0;
    for (i = s; i < list.length; i++) {
        if (i > TOO_MANY) {
            [self performSelector:@selector(checkLocationsStartingAt:)
                       withObject:@(i) 
                       afterDelay:0.001];
            return;
        } else {
            // check element at i
        }
    }
}

参见:NSObject Reference