将方法作为 SEL 参数传递给另一个类方法
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【中文标题】将方法作为 SEL 参数传递给另一个类方法【英文标题】:Pass method as an SEL argument to another class method 【发布时间】:2011-08-16 17:44:13 【问题描述】:我有一个 appDelegate,它初始化了一个名为 LocationService 的类的实例。 我只是想通过 init 向这个实例传递一个该类将运行的方法。
我遇到了这个异常:
2011-08-16 20:38:15.233 WalklogAnywhere[8258:307] -[LocationService setBackgroundActionMethod:]: unrecognized selector sent to instance 0x17a740
2011-08-16 20:38:15.249 WalklogAnywhere[8258:307] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[LocationService setBackgroundActionMethod:]: unrecognized selector sent to instance 0x17a740'
*** Call stack at first throw:
(
0 CoreFoundation 0x314d0987 __exceptionPreprocess + 114
1 libobjc.A.dylib 0x319a149d objc_exception_throw + 24
2 CoreFoundation 0x314d2133 -[NSObject(NSObject) doesNotRecognizeSelector:] + 102
3 CoreFoundation 0x31479aa9 ___forwarding___ + 508
4 CoreFoundation 0x31479860 _CF_forwarding_prep_0 + 48
5 WalklogAnywhere 0x00004013 -[LocationService initWithBackgroundMethod:] + 206
6 WalklogAnywhere 0x0000246b -[WalklogAnywhereAppDelegate application:didFinishLaunchingWithOptions:] + 110
7 UIKit 0x338dabc5 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 772
8 UIKit 0x338d6259 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 272
9 UIKit 0x338a248b -[UIApplication handleEvent:withNewEvent:] + 1114
10 UIKit 0x338a1ec9 -[UIApplication sendEvent:] + 44
11 UIKit 0x338a1907 _UIApplicationHandleEvent + 5090
12 GraphicsServices 0x35d66f03 PurpleEventCallback + 666
13 CoreFoundation 0x314656ff __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 26
14 CoreFoundation 0x314656c3 __CFRunLoopDoSource1 + 166
15 CoreFoundation 0x31457f7d __CFRunLoopRun + 520
16 CoreFoundation 0x31457c87 CFRunLoopRunSpecific + 230
17 CoreFoundation 0x31457b8f CFRunLoopRunInMode + 58
18 UIKit 0x338d5309 -[UIApplication _run] + 380
19 UIKit 0x338d2e93 UIApplicationMain + 670
20 WalklogAnywhere 0x000021bb main + 70
21 WalklogAnywhere 0x00002170 start + 40
)
terminate called after throwing an instance of 'NSException'
这是我的应用程序委托类方法,它初始化 LocationService 实例:
-(void) backgroundLocationUpdate
NSLog(@"location is updated in background");
#pragma mark -
#pragma mark Application lifecycle
- (BOOL)application:(UIApplication *)application
didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
// Override point for customization after application launch.
[self.window makeKeyAndVisible];
locationService = [[LocationService alloc]
initWithBackgroundMethod:@selector(backgroundLocationUpdate:)];
[locationService startForegroundService];
storageService = [[StorageService alloc] init];
[self loadApplicationData];
return YES;
这是 LocationService 类方法:
-(id) initWithBackgroundMethod:(SEL)selector
self = [super init];
if (self != nil)
self.locationManager = [[CLLocationManager alloc] init];
self.locationManager.delegate = self;
locationManager.desiredAccuracy = kCLLocationAccuracyBest;
self.backgroundActionMethod = selector;
return self;
请帮帮我。 非常感谢!
【问题讨论】:
【参考方案1】:选择器只是一个方法的名称。它与类无关,也与类的实例无关。
如果你想有一种回调,使用选择器,你必须提供一个目标对象以及选择器。
然后,调用目标对象的选择器,使用继承自 NSObject 的 performSelector
方法。
有关错误检查,请参阅respondToSelector
方法。
【讨论】:
【参考方案2】:删除 backgroundLocationUpdate 旁边的冒号,如下所示:
[self.window makeKeyAndVisible]; locationService = [[LocationService alloc] initWithBackgroundMethod:@selector(backgroundLocationUpdate)];
因为冒号使它寻找带有 (id)sender 参数的方法。
【讨论】:
【参考方案3】:错误来自这一行:
self.backgroundActionMethod = selector;
我猜你实际上没有 backgroundActionMethod 属性,因为没有 -setBackgroundActionMethod:
方法。
【讨论】:
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