iOS 查找代码里的crashes

iOS中在非主线程更新UI会有crashes闪退提示

UI在主线程之外更新了的cash.png

解决办法就是将产生crashes的代码放到主线程执行就可以了，但该代码块有时候不能很直观的看出来，本篇记录下如何便捷的找出crashes代码块。

往工程里添加PSPDFUIKitMainThreadGuard.m文件,完整代码如下👇

// Taken from the commercial iOS PDF framework http://pspdfkit.com.
// Copyright (c) 2014 Peter Steinberger, PSPDFKit GmbH. All rights reserved.
// Licensed under MIT (http://opensource.org/licenses/MIT)
//
// You should only use this in debug builds. It doesn't use private API, but I wouldn't ship it.

// PLEASE DUPE rdar://27192338 (https://openradar.appspot.com/27192338) if you would like to see this in UIKit.

#import <objc/runtime.h>
#import <objc/message.h>
#import <UIKit/UIKit.h>

#define PSPDFAssert(expression, ...) \
do { if(!(expression)) { \
NSLog(@"%@", [NSString stringWithFormat: @"Assertion failure: %s in %s on line %s:%d. %@", #expression, __PRETTY_FUNCTION__, __FILE__, __LINE__, [NSString stringWithFormat:@"" __VA_ARGS__]]); \
abort(); }} while(0)

// Compile-time selector checks.
#if DEBUG
#define PROPERTY(propName) NSStringFromSelector(@selector(propName))
#else
#define PROPERTY(propName) @#propName
#endif


// http://www.mikeash.com/pyblog/friday-qa-2010-01-29-method-replacement-for-fun-and-profit.html
BOOL PSPDFReplaceMethodWithBlock(Class c, SEL origSEL, SEL newSEL, id block) {
    //    NSCParameterAssert(c);
    //    NSCParameterAssert(origSEL);
    //    NSCParameterAssert(newSEL);
    //    NSCParameterAssert(block);
    
    if ([c instancesRespondToSelector:newSEL]) return YES; // Selector already implemented, skip silently.
    
    Method origMethod = class_getInstanceMethod(c, origSEL);
    
    // Add the new method.
    IMP impl = imp_implementationWithBlock(block);
    if (!class_addMethod(c, newSEL, impl, method_getTypeEncoding(origMethod))) {
        //        PSPDFLogError(@"Failed to add method: %@ on %@", NSStringFromSelector(newSEL), c);
        return NO;
    }else {
        Method newMethod = class_getInstanceMethod(c, newSEL);
        
        // If original doesn't implement the method we want to swizzle, create it.
        if (class_addMethod(c, origSEL, method_getImplementation(newMethod), method_getTypeEncoding(origMethod))) {
            class_replaceMethod(c, newSEL, method_getImplementation(origMethod), method_getTypeEncoding(newMethod));
        }else {
            method_exchangeImplementations(origMethod, newMethod);
        }
    }
    return YES;
}

SEL _PSPDFPrefixedSelector(SEL selector) {
    return NSSelectorFromString([NSString stringWithFormat:@"pspdf_%@", NSStringFromSelector(selector)]);
}


void PSPDFAssertIfNotMainThread(void) {
    PSPDFAssert(NSThread.isMainThread, @"\nERROR: All calls to UIKit need to happen on the main thread. You have a bug in your code. Use dispatch_async(dispatch_get_main_queue(), ^{ ... }); if you're unsure what thread you're in.\n\nBreak on PSPDFAssertIfNotMainThread to find out where.\n\nStacktrace: %@", NSThread.callStackSymbols);
}

__attribute__((constructor)) static void PSPDFUIKitMainThreadGuard(void) {
    @autoreleasepool {
        for (NSString *selStr in @[PROPERTY(setNeedsLayout), PROPERTY(setNeedsDisplay), PROPERTY(setNeedsDisplayInRect:)]) {
            SEL selector = NSSelectorFromString(selStr);
            SEL newSelector = NSSelectorFromString([NSString stringWithFormat:@"pspdf_%@", selStr]);
            if ([selStr hasSuffix:@":"]) {
                PSPDFReplaceMethodWithBlock(UIView.class, selector, newSelector, ^(__unsafe_unretained UIView *_self, CGRect r) {
                    // Check for window, since *some* UIKit methods are indeed thread safe.
                    // https://developer.apple.com/library/ios/#releasenotes/General/WhatsNewIniPhoneOS/Articles/iPhoneOS4.html
                    /*
                     Drawing to a graphics context in UIKit is now thread-safe. Specifically:
                     The routines used to access and manipulate the graphics context can now correctly handle contexts residing on different threads.
                     String and image drawing is now thread-safe.
                     Using color and font objects in multiple threads is now safe to do.
                     */
                    if (_self.window) PSPDFAssertIfNotMainThread();
                    ((void ( *)(id, SEL, CGRect))objc_msgSend)(_self, newSelector, r);
                });
            }else {
                PSPDFReplaceMethodWithBlock(UIView.class, selector, newSelector, ^(__unsafe_unretained UIView *_self) {
                    if (_self.window) {
                        if (!NSThread.isMainThread) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
                            dispatch_queue_t queue = dispatch_get_current_queue();
#pragma clang diagnostic pop
                            // iOS 8 layouts the MFMailComposeController in a background thread on an UIKit queue.
                            // https://github.com/PSPDFKit/PSPDFKit/issues/1423
                            if (!queue || !strstr(dispatch_queue_get_label(queue), "UIKit")) {
                                PSPDFAssertIfNotMainThread();
                            }
                        }
                    }
                    ((void ( *)(id, SEL))objc_msgSend)(_self, newSelector);
                });
            }
        }
    }
}

build一下，这时在左边的线程树，可以找到你自己编写的类文件名，点击该类文件名跳转到对应的crashes代码块，然后将该代码添加到主线程执行就可以了

crashes显示信息.png WechatIMG8.png

本来我是想打dispatch_async，但代码提示却打出了dispatch_main_async_safe

dispatch_async(dispatch_get_main_queue(), ^{
           [self.tableView reloadData];
        });

dispatch_main_async_safe(^{
        [self.tableView reloadData];
    });

刚看dispatch_main_async_safe感觉挺陌生的，点击进去发觉原来是SDWebImage定义的一个主线程安全，源码如下

#ifndef dispatch_main_async_safe
#define dispatch_main_async_safe(block)\
    if (strcmp(dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL), dispatch_queue_get_label(dispatch_get_main_queue())) == 0) {\
        block();\
    } else {\
        dispatch_async(dispatch_get_main_queue(), block);\
    }
#endif

SDWebImage 上关于 dispatch_main_async_safe 的链接

🔚