我得到ARC编译器的以下警告:
"performSelector may cause a leak because its selector is unknown".
这是我正在做的:
[_controller performSelector:NSSelectorFromString(@"someMethod")];
为什么我得到这个警告?我理解编译器不能检查选择器是否存在,但为什么会导致泄漏?我怎样才能改变我的代码,让我不再得到这个警告呢?
我得到ARC编译器的以下警告:
"performSelector may cause a leak because its selector is unknown".
这是我正在做的:
[_controller performSelector:NSSelectorFromString(@"someMethod")];
为什么我得到这个警告?我理解编译器不能检查选择器是否存在,但为什么会导致泄漏?我怎样才能改变我的代码,让我不再得到这个警告呢?
当前回答
这段代码不涉及编译器标志或直接运行时调用:
SEL selector = @selector(zeroArgumentMethod);
NSMethodSignature *methodSig = [[self class] instanceMethodSignatureForSelector:selector];
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
[invocation setSelector:selector];
[invocation setTarget:self];
[invocation invoke];
NSInvocation允许设置多个参数,因此与performSelector不同,这将适用于任何方法。
其他回答
如果你不需要传递任何参数,一个简单的解决方法是使用valueForKeyPath。这甚至可以在Class对象上实现。
NSString *colorName = @"brightPinkColor";
id uicolor = [UIColor class];
if ([uicolor respondsToSelector:NSSelectorFromString(colorName)]){
UIColor *brightPink = [uicolor valueForKeyPath:colorName];
...
}
在项目生成设置中,在其他警告标志(WARNING_CFLAGS)下添加 -Wno-arc-performSelector-leaks
现在只需确保所调用的选择器不会导致对象被保留或复制。
这里有很多答案,但由于这个有点不同,我把几个答案结合起来,我想我应该把它放进去。我使用一个NSObject类别检查,以确保选择器返回void,也抑制编译器警告。
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import "Debug.h" // not given; just an assert
@interface NSObject (Extras)
// Enforce the rule that the selector used must return void.
- (void) performVoidReturnSelector:(SEL)aSelector withObject:(id)object;
- (void) performVoidReturnSelector:(SEL)aSelector;
@end
@implementation NSObject (Extras)
// Apparently the reason the regular performSelect gives a compile time warning is that the system doesn't know the return type. I'm going to (a) make sure that the return type is void, and (b) disable this warning
// See http://stackoverflow.com/questions/7017281/performselector-may-cause-a-leak-because-its-selector-is-unknown
- (void) checkSelector:(SEL)aSelector {
// See http://stackoverflow.com/questions/14602854/objective-c-is-there-a-way-to-check-a-selector-return-value
Method m = class_getInstanceMethod([self class], aSelector);
char type[128];
method_getReturnType(m, type, sizeof(type));
NSString *message = [[NSString alloc] initWithFormat:@"NSObject+Extras.performVoidReturnSelector: %@.%@ selector (type: %s)", [self class], NSStringFromSelector(aSelector), type];
NSLog(@"%@", message);
if (type[0] != 'v') {
message = [[NSString alloc] initWithFormat:@"%@ was not void", message];
[Debug assertTrue:FALSE withMessage:message];
}
}
- (void) performVoidReturnSelector:(SEL)aSelector withObject:(id)object {
[self checkSelector:aSelector];
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
// Since the selector (aSelector) is returning void, it doesn't make sense to try to obtain the return result of performSelector. In fact, if we do, it crashes the app.
[self performSelector: aSelector withObject: object];
#pragma clang diagnostic pop
}
- (void) performVoidReturnSelector:(SEL)aSelector {
[self checkSelector:aSelector];
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
[self performSelector: aSelector];
#pragma clang diagnostic pop
}
@end
不要压制警告!
有不少于12个可选的解决方案来修补编译器。 虽然在第一次实现时你很聪明,但地球上很少有工程师能追随你的脚步,而这段代码最终会崩溃。
安全的路线:
所有这些解决方案都是可行的,只是在一定程度上与您的初衷有所不同。假设param可以为nil:
安全路线,相同的概念行为:
// GREAT
[_controller performSelectorOnMainThread:selector withObject:anArgument waitUntilDone:YES];
[_controller performSelectorOnMainThread:selector withObject:anArgument waitUntilDone:YES modes:@[(__bridge NSString *)kCFRunLoopDefaultMode]];
[_controller performSelector:selector onThread:[NSThread mainThread] withObject:anArgument waitUntilDone:YES];
[_controller performSelector:selector onThread:[NSThread mainThread] withObject:anArgument waitUntilDone:YES modes:@[(__bridge NSString *)kCFRunLoopDefaultMode]];
安全路线,行为稍有不同:
(见此回复) 使用任何线程代替[NSThread主线程]。
// GOOD
[_controller performSelector:selector withObject:anArgument afterDelay:0];
[_controller performSelector:selector withObject:anArgument afterDelay:0 inModes:@[(__bridge NSString *)kCFRunLoopDefaultMode]];
[_controller performSelectorOnMainThread:selector withObject:anArgument waitUntilDone:NO];
[_controller performSelectorOnMainThread:selector withObject:anArgument waitUntilDone:NO];
[_controller performSelectorOnMainThread:selector withObject:anArgument waitUntilDone:NO modes:@[(__bridge NSString *)kCFRunLoopDefaultMode]];
[_controller performSelectorInBackground:selector withObject:anArgument];
[_controller performSelector:selector onThread:[NSThread mainThread] withObject:anArgument waitUntilDone:NO];
[_controller performSelector:selector onThread:[NSThread mainThread] withObject:anArgument waitUntilDone:NO modes:@[(__bridge NSString *)kCFRunLoopDefaultMode]];
危险的路线
需要某种编译器静音,这是必然的破坏。请注意,目前,它确实在Swift中中断了。
// AT YOUR OWN RISK
[_controller performSelector:selector];
[_controller performSelector:selector withObject:anArgument];
[_controller performSelector:selector withObject:anArgument withObject:nil];
为了让Scott Thompson的宏更通用:
// String expander
#define MY_STRX(X) #X
#define MY_STR(X) MY_STRX(X)
#define MYSilenceWarning(FLAG, MACRO) \
_Pragma("clang diagnostic push") \
_Pragma(MY_STR(clang diagnostic ignored MY_STR(FLAG))) \
MACRO \
_Pragma("clang diagnostic pop")
然后这样使用它:
MYSilenceWarning(-Warc-performSelector-leaks,
[_target performSelector:_action withObject:self];
)