> For the complete documentation index, see [llms.txt](https://philm.gitbook.io/philm-ios-wiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://philm.gitbook.io/philm-ios-wiki/mei-zhou-yue-du/qing-liang-ji-di-feng-xian-ios-re-geng-xin-fang-an.md).

# 轻量级低风险 iOS 热更新方案

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。

要达到这个目的，Native 层只要透出两种能力就基本可以了：

1. 在任意方法前后注入代码的能力，可能的话最好还能替换掉。
2. 调用任意类/实例方法的能力。

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？

选择 Aspects 的原因是它已经经过了验证，不光是功能上的，更重要的是可以通过 AppStore 的审核。

> 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.

Aspects 使用姿势：

> \[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。

这种方式的安全性在于：

1. 不需要中间 JS 文件，准备工作全部在 Native 端完成。
2. 没有使用 App Store 不友好的类/方法。

**Demo**

假设线上运行这这样一个 Class，由于疏忽，没有对参数做检查，导致特定情况下会 Crash。

> @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

现在我们要避免 Crash，就可以通过这种方式来修复

> \[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];

运行一下看看

> 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

It Works, 是不是有那么点意思了。以下是可以正常运行的代码，仅供参考。

> \#import \<Aspects.h>
>
> \#import \<objc/runtime.h>
>
> \#import \<JavaScriptCore/JavaScriptCore.h>
>
> @interface Felix: NSObject
>
> * (void)fixIt;
> * (void)evalString:(NSString \*)javascriptString;
>
> @end
>
> @implementation Felix
>
> * (Felix \*)sharedInstance
>
> {
>
> ```
> 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\];
> ```
>
> }
>
> * (JSContext \*)context
>
> {
>
> ```
> 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
>
> }
>
> * (void)fixIt
>
> {
>
> ```
> \[self context\]\[@"fixInstanceMethodBefore"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
>
>     \[self \_fixWithMethod:NO aspectionOptions:AspectPositionBefore instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
>
> };
> ```
>
> ```
> \[self context\]\[@"fixInstanceMethodReplace"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
>
>     \[self \_fixWithMethod:NO aspectionOptions:AspectPositionInstead instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
>
> };
> ```
>
> ```
> \[self context\]\[@"fixInstanceMethodAfter"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
>
>     \[self \_fixWithMethod:NO aspectionOptions:AspectPositionAfter instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
>
> };
> ```
>
> ```
> \[self context\]\[@"fixClassMethodBefore"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
>
>     \[self \_fixWithMethod:YES aspectionOptions:AspectPositionBefore instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
>
> };
> ```
>
> ```
> \[self context\]\[@"fixClassMethodReplace"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
>
>     \[self \_fixWithMethod:YES aspectionOptions:AspectPositionInstead instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
>
> };
> ```
>
> ```
> \[self context\]\[@"fixClassMethodAfter"\] = ^\(NSString \*instanceName, NSString \*selectorName, JSValue \*fixImpl\) {
>
>     \[self \_fixWithMethod:YES aspectionOptions:AspectPositionAfter instanceName:instanceName selectorName:selectorName fixImpl:fixImpl\];
>
> };
> ```
>
> ```
> \[self context\]\[@"runClassWithNoParamter"\] = ^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