- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    
}

在touchesBegan方法设置断点，控制台输入thread backtrace all，获取调用流程（调用顺序为打印出来的内容，从下往上执行：
1、线程“com.apple.main-thread”从“dyld`start + 520”开始执行。
2、线程“com.apple.uikit.eventfetch-thread”从“libsystem_kernel.dylib`__workq_kernreturn + 8”开始执行。

image.png

(lldb) thread backtrace all
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 3.1
  * frame #0: 0x0000000104b81e14 Demo`-[ViewController touchesBegan:withEvent:](self=0x000000015ff04c90, _cmd="touchesBegan:withEvent:", touches=1 element, event=0x0000600000730cc0) at ViewController.m:32:1
    frame #1: 0x0000000184dbd96c UIKitCore`forwardTouchMethod + 316
    frame #2: 0x0000000184dcd65c UIKitCore`-[UIWindow _sendTouchesForEvent:] + 548
    frame #3: 0x0000000184dcf36c UIKitCore`-[UIWindow sendEvent:] + 4332
    frame #4: 0x0000000184da70fc UIKitCore`-[UIApplication sendEvent:] + 784
    frame #5: 0x0000000184e3559c UIKitCore`__dispatchPreprocessedEventFromEventQueue + 7720
    frame #6: 0x0000000184e37620 UIKitCore`__processEventQueue + 6764
    frame #7: 0x0000000184e2f540 UIKitCore`__eventFetcherSourceCallback + 184
    frame #8: 0x0000000180362234 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24
    frame #9: 0x0000000180362134 CoreFoundation`__CFRunLoopDoSource0 + 204
    frame #10: 0x00000001803614c4 CoreFoundation`__CFRunLoopDoSources0 + 256
    frame #11: 0x000000018035ba18 CoreFoundation`__CFRunLoopRun + 744
    frame #12: 0x000000018035b218 CoreFoundation`CFRunLoopRunSpecific + 572
    frame #13: 0x000000018c25f60c GraphicsServices`GSEventRunModal + 160
    frame #14: 0x0000000184d88a98 UIKitCore`-[UIApplication _run] + 992
    frame #15: 0x0000000184d8d634 UIKitCore`UIApplicationMain + 112
    frame #16: 0x0000000104b82080 Demo`main(argc=1, argv=0x000000016b27dc88) at main.m:21:12
    frame #17: 0x0000000104d9dcd8 dyld_sim`start_sim + 20
    frame #18: 0x0000000104f1108c dyld`start + 520
  thread #5, name = 'com.apple.uikit.eventfetch-thread'
    frame #0: 0x00000001cc055fcc libsystem_kernel.dylib`mach_msg_trap + 8
    frame #1: 0x00000001cc056430 libsystem_kernel.dylib`mach_msg + 72
    frame #2: 0x000000018036176c CoreFoundation`__CFRunLoopServiceMachPort + 368
    frame #3: 0x000000018035bb78 CoreFoundation`__CFRunLoopRun + 1096
    frame #4: 0x000000018035b218 CoreFoundation`CFRunLoopRunSpecific + 572
    frame #5: 0x0000000180827828 Foundation`-[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 232
    frame #6: 0x0000000180827ae0 Foundation`-[NSRunLoop(NSRunLoop) runUntilDate:] + 88
    frame #7: 0x0000000184e3f01c UIKitCore`-[UIEventFetcher threadMain] + 472
    frame #8: 0x0000000180851578 Foundation`__NSThread__start__ + 792
    frame #9: 0x00000001cc0b16c8 libsystem_pthread.dylib`_pthread_start + 116
  thread #9
    frame #0: 0x00000001cc057ce4 libsystem_kernel.dylib`__workq_kernreturn + 8
(lldb)