frame #0: 0x39ccfe58 libobjc.A.dylib`realizeClass(class_t*) + 412
frame #1: 0x39cca094 libobjc.A.dylib`prepareForMethodLookup + 84
frame #2: 0x39cc9f9a libobjc.A.dylib`lookUpMethod + 46
frame #3: 0x39cc9f66 libobjc.A.dylib`_class_lookupMethodAndLoadCache3 + 18
frame #4: 0x39cc961a libobjc.A.dylib`objc_msgSend_uncached + 26
frame #5: 0x39cca1cc libobjc.A.dylib`_class_initialize + 232
frame #6: 0x39cca0da libobjc.A.dylib`prepareForMethodLookup + 154
frame #7: 0x39cc9f9a libobjc.A.dylib`lookUpMethod + 46
frame #8: 0x39cc9f66 libobjc.A.dylib`_class_lookupMethodAndLoadCache3 + 18
frame #9: 0x39cc961a libobjc.A.dylib`objc_msgSend_uncached + 26
frame #10: 0x33c75082 UIKit`-[UIWindow _sendGesturesForEvent:] + 410
frame #11: 0x33c74db2 UIKit`-[UIWindow sendEvent:] + 90
frame #12: 0x33c62800 UIKit`-[UIApplication sendEvent:] + 380
frame #13: 0x33c6211a UIKit`_UIApplicationHandleEvent + 6154
frame #14: 0x359585a2 GraphicsServices`_PurpleEventCallback + 590
frame #15: 0x359581d2 GraphicsServices`PurpleEventCallback + 34
frame #16: 0x31e2f172 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 34
frame #17: 0x31e2f116 CoreFoundation`__CFRunLoopDoSource1 + 138
frame #18: 0x31e2df98 CoreFoundation`__CFRunLoopRun + 1384
frame #19: 0x31da0ebc CoreFoundation`CFRunLoopRunSpecific + 356
frame #20: 0x31da0d48 CoreFoundation`CFRunLoopRunInMode + 104
frame #21: 0x359572ea GraphicsServices`GSEventRunModal + 74
frame #22: 0x33cb6300 UIKit`UIApplicationMain + 1120
frame #23: 0x0000fcb0 XFDownloadDemo`main(argc=1, argv=0x2fdfbd08) + 172 at main.m:16
* thread＃1：tid = 0x2403,0x39ccfe58 libobjc.A.dylib`realizeClass（class_t *）+ 412，queue ='com.apple.main-thread，stop reason = EXC_BAD_ACCESS（code = 1，address = 0x7636c678 ）
我的应用有什么问题？令我感到困惑的是，所有崩溃调用堆栈都在系统API中。