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

因为您正在使用ARC,所以必须使用iOS 4.0或更高版本。这意味着你可以使用积木。如果不是记住要执行的选择器,而是取一个块,ARC将能够更好地跟踪实际发生的事情,并且不必冒意外引入内存泄漏的风险。

其他回答

我没有使用块方法,这给我带来了一些问题:

    IMP imp = [_controller methodForSelector:selector];
    void (*func)(id, SEL) = (void *)imp;

我将使用NSInvocation,像这样:

    -(void) sendSelectorToDelegate:(SEL) selector withSender:(UIButton *)button 

    if ([delegate respondsToSelector:selector])
    {
    NSMethodSignature * methodSignature = [[delegate class]
                                    instanceMethodSignatureForSelector:selector];
    NSInvocation * delegateInvocation = [NSInvocation
                                   invocationWithMethodSignature:methodSignature];


    [delegateInvocation setSelector:selector];
    [delegateInvocation setTarget:delegate];

    // remember the first two parameter are cmd and self
    [delegateInvocation setArgument:&button atIndex:2];
    [delegateInvocation invoke];
    }

您还可以在这里使用协议。因此,创建一个这样的协议:

@protocol MyProtocol
-(void)doSomethingWithObject:(id)object;
@end

在需要调用选择器的类中,有一个@属性。

@interface MyObject
    @property (strong) id<MyProtocol> source;
@end

当你需要在MyObject的实例中调用@selector(doSomethingWithObject:)时,这样做:

[self.source doSomethingWithObject:object];

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