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
在编译器允许覆盖警告之前,可以使用运行时作为一种变通方法。
你需要标题:
#import <objc/message.h>
然后试试下面的方法:
// For strict compilers.
((id(*)(id,SEL))objc_msgSend)(_controller, sel_getUid("someMethod"));
OR
// Old answer's code:
objc_msgSend(_controller, NSSelectorFromString(@"someMethod"));
而不是:
[_controller performSelector:NSSelectorFromString(@"someMethod")];
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];
}
下面是基于上面给出的答案更新的宏。这应该允许您使用return语句来包装代码。
#define SUPPRESS_PERFORM_SELECTOR_LEAK_WARNING(code) \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Warc-performSelector-leaks\"") \
code; \
_Pragma("clang diagnostic pop") \
SUPPRESS_PERFORM_SELECTOR_LEAK_WARNING(
return [_target performSelector:_action withObject:self]
);
要使用执行选择器忽略文件中的错误,添加一个#pragma,如下所示:
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
这将忽略这一行上的警告,但仍然允许它贯穿整个项目的其余部分。
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];
...
}
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];