我们都知道苹果对 Hotfix 抓得比较严，强大好用的 JSPatch 也成为了过去式。但即使测试地再细致，也难保线上 App 不出问题，小问题还能忍忍，大问题就得重新走发布流程，然后等待审核通过，等待用户升级，周期长且麻烦。如果有一种方式相对比较安全，不需要 JSPatch 那么完善，但也足够应付一般场景，使用起来还比较轻量就好了，这也是本文要探讨的主题。
第 2 点不难，只要把 [NSObject performSelector:...] 那一套通过 JSContext 暴露出来即可。难的是第 1 点。其实细想一下，这不就是 AOP 么，而 iOS 有一个很方便的 AOP Library:Aspects，只要把它的几个方法通过 JSContext 暴露给 JS 不就可以了么？
This is stable and used in hundreds of apps since it’s part of PSPDFKit, an iOS PDF framework that ships with apps like Dropbox or Evernote.
[UIViewController aspect_hookSelector:@selector(viewWillAppear:) withOptions:AspectPositionAfter usingBlock:^(id<AspectInfo> aspectInfo, BOOL animated) {
NSLog\(@"View Controller %@ will appear animated: %tu", aspectInfo.instance, animated\);
} error:NULL];
前插、后插、替换某个方法都可以。使用类的方式很简单，NSClassFromString 即可，Selector 也一样 NSSelectorFromString，这样就能通过外部传入 String，内部动态构造 Class 和 Selector 来达到 Fix 的效果了。
@interface MightyCrash: NSObject
(float)divideUsingDenominator:(NSInteger)denominator;
@end
@implementation MightyCrash
// 传一个 0 就 gg 了
(float)divideUsingDenominator:(NSInteger)denominator
{
return 1.f/denominator;
}
@end
[Felix fixIt];
NSString *fixScriptString = @"
fixInstanceMethodReplace('MightyCrash', 'divideUsingDenominator:', function(instance, originInvocation, originArguments){
if \(originArguments\[0\] == 0\) {
console.log\('zero goes here'\);
} else {
runInvocation\(originInvocation\);
}
});
";
[Felix evalString:fixScriptString];
MightyCrash *mc = [[MightyCrash alloc] init];
float result = [mc divideUsingDenominator:3];
NSLog(@"result: %.3f", result);
result = [mc divideUsingDenominator:0];
NSLog(@"won't crash");
// output
// result: 0.333
// Javascript log: zero goes here
// won't crash
#import <Aspects.h>
#import <objc/runtime.h>
#import <JavaScriptCore/JavaScriptCore.h>
@interface Felix: NSObject
(void)evalString:(NSString *)javascriptString;
@end
@implementation Felix
{
static Felix \*sharedInstance = nil;
static dispatch\_once\_t onceToken;
dispatch\_once\(&onceToken, ^{
sharedInstance = \[\[self alloc\] init\];
}\);
return sharedInstance;
}
(void)evalString:(NSString *)javascriptString
{
\[\[self context\] evaluateScript:javascriptString\];
}
{
static JSContext \*\_context;
static dispatch\_once\_t onceToken;
dispatch\_once\(&onceToken, ^{
\_context = \[\[JSContext alloc\] init\];
\[\_context setExceptionHandler:^\(JSContext \*context, JSValue \*value\) {
NSLog\(@"Oops: %@", value\);
}\];
}\);
return \_context;
}
(void)_fixWithMethod:(BOOL)isClassMethod aspectionOptions:(AspectOptions)option instanceName:(NSString *)instanceName selectorName:(NSString *)selectorName fixImpl:(JSValue *)fixImpl {
Class klass = NSClassFromString(instanceName);
if (isClassMethod) {
klass = object\_getClass\(klass\);
}
SEL sel = NSSelectorFromString(selectorName);
[klass aspect_hookSelector:sel withOptions:option usingBlock:^(id<AspectInfo> aspectInfo){
\[fixImpl callWithArguments:@\[aspectInfo.instance, aspectInfo.originalInvocation, aspectInfo.arguments\]\];
} error:nil];
}
(id)_runClassWithClassName:(NSString *)className selector:(NSString *)selector obj1:(id)obj1 obj2:(id)obj2 {
Class klass = NSClassFromString(className);
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
return \[klass performSelector:NSSelectorFromString\(selector\) withObject:obj1 withObject:obj2\];
#pragma clang diagnostic pop
}
(id)_runInstanceWithInstance:(id)instance selector:(NSString *)selector obj1:(id)obj1 obj2:(id)obj2 {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
return \[instance performSelector:NSSelectorFromString\(selector\) withObject:obj1 withObject:obj2\];
#pragma clang diagnostic pop
}
{
\[self context\]\[@"fixInstanceMethodBefore"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
\[self \_fixWithMethod:NO aspectionOptions:AspectPositionBefore instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
};
\[self context\]\[@"fixInstanceMethodReplace"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
\[self \_fixWithMethod:NO aspectionOptions:AspectPositionInstead instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
};
\[self context\]\[@"fixInstanceMethodAfter"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
\[self \_fixWithMethod:NO aspectionOptions:AspectPositionAfter instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
};
\[self context\]\[@"fixClassMethodBefore"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
\[self \_fixWithMethod:YES aspectionOptions:AspectPositionBefore instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
};
\[self context\]\[@"fixClassMethodReplace"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
\[self \_fixWithMethod:YES aspectionOptions:AspectPositionInstead instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
};
\[self context\]\[@"fixClassMethodAfter"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
\[self \_fixWithMethod:YES aspectionOptions:AspectPositionAfter instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
};
\[self context\]\[@"runClassWithNoParamter"\] = ^id\(NSString \*className, NSString \*selectorName\) {
return \[self \_runClassWithClassName:className selector:selectorName obj1:nil obj2:nil\];
};
\[self context\]\[@"runClassWith1Paramter"\] = ^id\(NSString \*className, NSString \*selectorName, id obj1\) {
return \[self \_runClassWithClassName:className selector:selectorName obj1:obj1 obj2:nil\];
};
\[self context\]\[@"runClassWith2Paramters"\] = ^id\(NSString \*className, NSString \*selectorName, id obj1, id obj2\) {
return \[self \_runClassWithClassName:className selector:selectorName obj1:obj1 obj2:obj2\];
};
\[self context\]\[@"runVoidClassWithNoParamter"\] = ^\(NSString \*className, NSString \*selectorName\) {
\[self \_runClassWithClassName:className selector:selectorName obj1:nil obj2:nil\];
};
\[self context\]\[@"runVoidClassWith1Paramter"\] = ^\(NSString \*className, NSString \*selectorName, id obj1\) {
\[self \_runClassWithClassName:className selector:selectorName obj1:obj1 obj2:nil\];
};
\[self context\]\[@"runVoidClassWith2Paramters"\] = ^\(NSString \*className, NSString \*selectorName, id obj1, id obj2\) {
\[self \_runClassWithClassName:className selector:selectorName obj1:obj1 obj2:obj2\];
};
\[self context\]\[@"runInstanceWithNoParamter"\] = ^id\(id instance, NSString \*selectorName\) {
return \[self \_runInstanceWithInstance:instance selector:selectorName obj1:nil obj2:nil\];
};
\[self context\]\[@"runInstanceWith1Paramter"\] = ^id\(id instance, NSString \*selectorName, id obj1\) {
return \[self \_runInstanceWithInstance:instance selector:selectorName obj1:obj1 obj2:nil\];
};
\[self context\]\[@"runInstanceWith2Paramters"\] = ^id\(id instance, NSString \*selectorName, id obj1, id obj2\) {
return \[self \_runInstanceWithInstance:instance selector:selectorName obj1:obj1 obj2:obj2\];
};
\[self context\]\[@"runVoidInstanceWithNoParamter"\] = ^\(id instance, NSString \*selectorName\) {
\[self \_runInstanceWithInstance:instance selector:selectorName obj1:nil obj2:nil\];
};
\[self context\]\[@"runVoidInstanceWith1Paramter"\] = ^\(id instance, NSString \*selectorName, id obj1\) {
\[self \_runInstanceWithInstance:instance selector:selectorName obj1:obj1 obj2:nil\];
};
\[self context\]\[@"runVoidInstanceWith2Paramters"\] = ^\(id instance, NSString \*selectorName, id obj1, id obj2\) {
\[self \_runInstanceWithInstance:instance selector:selectorName obj1:obj1 obj2:obj2\];
};
\[self context\]\[@"runInvocation"\] = ^\(NSInvocation \*invocation\) {
\[invocation invoke\];
};
// helper
\[\[self context\] evaluateScript:@"var console = {}"\];
\[self context\]\[@"console"\]\[@"log"\] = ^\(id message\) {
NSLog\(@"Javascript log: %@",message\);
};
}
@end
