ios - 调动 NSObject 的 performSelector :withObject: gives EXC_BAD_ACCESS why?

Question

我正在尝试调配 NSObject 的 performSelector:withObject: rentzsch的 swizzling 库，代码如下:

#import "NSObject+xxxx.h"
#import "JRSwizzle.h"

@implementation NSObject (xxxx)
+ (void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        NSError *error;
        BOOL result = [[self class] jr_swizzleMethod:@selector(performSelector:withObject:) withMethod:@selector(xxxx_performSelector:withObject:) error:&error];
        if (!result || error) {
            NSLog(@"Can't swizzle methods - %@", [error description]);
        }else{
            NSLog(@"done");
        }      
    });
}

- (id)xxxx_performSelector:(SEL)aSelector withObject:(id)object{
    NSLog(@"called %@ %@",NSStringFromSelector(aSelector), [object description]);
    return [self xxxx_performSelector:aSelector withObject:object]; // when running it, Xcode stops and highlights this line
}

@end

我的问题是，为什么当我运行它时它会给我 EXC_BAD_ACCESS？
请注意，它总是在同一点失败。而且，我只是在追踪论点(没有其他魔法)。

这是我在控制台中得到的:

2014-04-01 17:36:40.368 xxxApp debug[7322:90b] done
2014-04-01 17:36:44.704 xxxApp debug[7322:90b] called layoutSublayersOfLayer: <CALayer: 0xcd75650>
2014-04-01 17:36:45.536 xxxApp debug[7322:90b] called layoutSublayersOfLayer: <CALayer: 0xcd76240>
2014-04-01 17:36:45.955 xxxApp debug[7322:90b] called layoutSublayersOfLayer: <CALayer: 0xcd76550>
2014-04-01 17:36:46.170 xxxApp debug[7322:90b] called layoutSublayersOfLayer: <CALayer: 0xcd7bce0>
2014-04-01 17:36:46.470 xxxApp debug[7322:90b] called layoutSublayersOfLayer: <UIWindowLayer: 0xcd78140>

这是回溯:

(lldb) bt
* thread #1: tid = 0x7bd49, 0x01e81de5 libobjc.A.dylib`objc_retain + 21, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x56e58965)
    frame #0: 0x01e81de5 libobjc.A.dylib`objc_retain + 21
  * frame #1: 0x000099f0 MyApp debug`-[NSObject(self=0x0f8432a0, _cmd=0x022bd138, aSelector=0x0083aae4, object=0x0f8424f0) xxxx_performSelector:withObject:] + 256 at NSObject+xxxx.m:44
    frame #2: 0x007e745a QuartzCore`-[CALayer layoutSublayers] + 148
    frame #3: 0x007db244 QuartzCore`CA::Layer::layout_if_needed(CA::Transaction*) + 380
    frame #4: 0x007e73a5 QuartzCore`-[CALayer layoutIfNeeded] + 160
    frame #5: 0x00a55ae3 UIKit`-[UIViewController window:setupWithInterfaceOrientation:] + 304
    frame #6: 0x0096baa7 UIKit`-[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:isRotating:] + 5212
    frame #7: 0x0096a646 UIKit`-[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:] + 82
    frame #8: 0x0096a518 UIKit`-[UIWindow _setRotatableViewOrientation:updateStatusBar:duration:force:] + 117
    frame #9: 0x0096a5a0 UIKit`-[UIWindow _setRotatableViewOrientation:duration:force:] + 67
    frame #10: 0x0096963a UIKit`__57-[UIWindow _updateToInterfaceOrientation:duration:force:]_block_invoke + 120
    frame #11: 0x0096959c UIKit`-[UIWindow _updateToInterfaceOrientation:duration:force:] + 400
    frame #12: 0x0096a2f3 UIKit`-[UIWindow setAutorotates:forceUpdateInterfaceOrientation:] + 870
    frame #13: 0x0096d8e6 UIKit`-[UIWindow setDelegate:] + 449
    frame #14: 0x00a47b77 UIKit`-[UIViewController _tryBecomeRootViewControllerInWindow:] + 180
    frame #15: 0x00963474 UIKit`-[UIWindow addRootViewControllerViewIfPossible] + 591
    frame #16: 0x009635ef UIKit`-[UIWindow _setHidden:forced:] + 312
    frame #17: 0x0096386b UIKit`-[UIWindow _orderFrontWithoutMakingKey] + 49
    frame #18: 0x0096e3c8 UIKit`-[UIWindow makeKeyAndVisible] + 65
    frame #19: 0x0091ebc0 UIKit`-[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 2097
    frame #20: 0x00923667 UIKit`-[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824
    frame #21: 0x00937f92 UIKit`-[UIApplication handleEvent:withNewEvent:] + 3517
    frame #22: 0x00938555 UIKit`-[UIApplication sendEvent:] + 85
    frame #23: 0x00925250 UIKit`_UIApplicationHandleEvent + 683
    frame #24: 0x0341af02 GraphicsServices`_PurpleEventCallback + 776
    frame #25: 0x0341aa0d GraphicsServices`PurpleEventCallback + 46
    frame #26: 0x02130ca5 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53
    frame #27: 0x021309db CoreFoundation`__CFRunLoopDoSource1 + 523
    frame #28: 0x0215b68c CoreFoundation`__CFRunLoopRun + 2156
    frame #29: 0x0215a9d3 CoreFoundation`CFRunLoopRunSpecific + 467
    frame #30: 0x0215a7eb CoreFoundation`CFRunLoopRunInMode + 123
    frame #31: 0x00922d9c UIKit`-[UIApplication _run] + 840
    frame #32: 0x00924f9b UIKit`UIApplicationMain + 1225
    frame #33: 0x00002997 MyApp debug`main(argc=1, argv=0xbfffedac) + 135 at main.m:16

Answer 1

简短的回答:

您的问题是 ARC，您应该可以通过添加 -fno-objc-arc 来解决它只在你的项目配置中的这个文件(构建阶段>编译源>编译器标志)另外确保你设置error至nil在 load在你调酒之前 - 这会在 ARC 下自动发生。

解释:

ARC 需要知道方法调用的返回类型，以及返回值的所有权，以便它可以适本地管理引用。这会导致 performSelector:withObject 出现问题。由于 Objective-C 中的选择器是无类型的，因此 ARC 无法知道返回类型。该方法声明返回id ，但使用适当的选择器实际上可能会返回 void - ARC 将尝试保留返回值，并且在实际上没有返回任何内容时这样做并不能很好地工作，因为在这种情况下返回值本质上是垃圾。

只为这一个文件关闭 ARC 没有显着影响，您的 xxxx_performSelector:withObject:不需要手动内存管理调用。

高温高压