Question

First please take a look at codes below

CoreLocationController.h
#import <Foundation/Foundation.h>
#import <CoreLocation/CoreLocation.h>

@protocol CoreLocationControllerDelegate     // Line 1
@required                       

- (void)locationUpdate:(CLLocation *)location;
- (void)locationError:(NSError *)error;

@end

/* Declare class named CoreLocationControll and inherited from CLLocationManagerDelegate */
@interface CoreLocationController : NSObject <CLLocationManagerDelegate> {
    CLLocationManager *locMgr;
    id delegate;
}

@property (nonatomic, retain) CLLocationManager *locMgr;            // claim setter and getter for locMgr
@property (nonatomic, assign) id delegate;                          // claim setter and getter for delegate

@end


CoreLcationController.m
#import "CoreLocationController.h"

@implementation CoreLocationController
@synthesize locMgr, delegate;

/* Is triggered by - (void)startUpdatingLocation from CoreLocationDemoViewController.m*/
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
    NSLog(@"CORE_LOCATION_CONTROLLER=======>DID_UPDATE_TO_LOCATION");
    if([self.delegate conformsToProtocol:@protocol(CoreLocationControllerDelegate)]) // line 2
        [self.delegate locationUpdate:newLocation];

}

My questions are what line 1 and line 2 do and why I looked up CoreLocationControllerDelegate but no reference on it

Answer 1

你们要求的是客观议定书宣言。该守则正在宣布一项名为“核心”的协议。简言之,议定书是一份方法清单,如果某一物体符合议定书,即可预期予以执行。

For example, the UITextFieldDelegate protocol contains the various methods that an object should or must implement if it wants to be the delegate for a text field.

第1行<代码>@required是指该物体必须采用下列方法以符合议定书。如果你宣布你的反对符合议定书,它必须执行这些方法,或者你会犯错误(或警告,我可以记住这些错误)。

Line 2 is a safety check to make sure that the delegate conforms to the protocol (in this case, that it implements the required methods) before the delegate methods are called. This prevents a runtime crash where an unrecognised selector is sent to the object.

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