如何解决使用ARC后出现的PerformSelector may cause a leak because its selector is unknown
2017-05-08 13:49
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问题描述
项目中使用到了从字符串创建选择器,编译时发现警告:"performSelector may cause a leak because its selector is unknown"(因为performSelector的选择器未知可能会引起泄漏),为什么在ARC模式下会出现这个警告?我用的是第二种方法。宏定义经过搜索后,在Stackoverflow上发现了一个令人满意的答案。见http://stackoverflow.com/questions/7017281/performselector-may-cause-a-leak-because-its-selector-is-unknown。
原因
在ARC模式下,运行时需要知道如何处理你正在调用的方法的返回值。这个返回值可以是任意值,如void,
int,
char,
NSString,
id等等。ARC通过头文件的函数定义来得到这些信息。所以平时我们用到的静态选择器就不会出现这个警告。因为在编译期间,这些信息都已经确定。
如:
... [someController performSelector:@selector(someMethod)]; ... - (void)someMethod { //bla bla... }
而使用
[someController performSelector: NSSelectorFromString(@"someMethod")];时ARC并不知道该方法的返回值是什么,以及该如何处理?该忽略?还是标记为
ns_returns_retained还是
ns_returns_autoreleased?
解决办法
1.使用函数指针方式
SEL selector = NSSelectorFromString(@"someMethod"); IMP imp = [_controller methodForSelector:selector]; void (*func)(id, SEL) = (void *)imp; func(_controller, selector);
当有额外参数时,如
SEL selector = NSSelectorFromString(@"processRegion:ofView:"); IMP imp = [_controller methodForSelector:selector]; CGRect (*func)(id, SEL, CGRect, UIView *) = (void *)imp; CGRect result = func(_controller, selector, someRect, someView);
2.使用宏忽略警告
#pragma clang diagnostic push #pragma clang diagnostic ignored "-Warc-performSelector-leaks" [someController performSelector: NSSelectorFromString(@"someMethod")] #pragma clang diagnostic pop
通过使用
#pragma clang diagnostic push/pop,你可以告诉Clang编译器仅仅为某一特定部分的代码来忽视特定警告。
如果需要忽视的警告有多处,可以定义一个宏
#define SuppressPerformSelectorLeakWarning(Stuff) \ do { \ _Pragma("clang diagnostic push") \ _Pragma("clang diagnostic ignored \"-Warc-performSelector-leaks\"") \ Stuff; \ _Pragma("clang diagnostic pop") \ } while (0)
在产生警告也就是
performSelector的地方用使用该宏,如
SuppressPerformSelectorLeakWarning( [_target performSelector:_action withObject:self] );
如果需要
performSelector返回值的话,
id result; SuppressPerformSelectorLeakWarning( result = [_target performSelector:_action withObject:self] );
3.使用afterDelay
[self performSelector:aSelector withObject:nil afterDelay:0.0];
如果在接受范围内,允许在下一个runloop执行,可以这么做。xCode5没问题,但据反映,xCode6的话这个不能消除警告。
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