angularjs 源码解析之injector

简介

injector是用来做参数自动注入的，例如

rush:js;"> function fn ($http,$scope,aService) { }

ng在运行时会把$http,aService 自动作为参数传入进行执行。

其实很容易想明白，injector做了两件事

1. 缓存那些service，以后作为参数注入
2. 分析参数列表，找到需要的参数注入

下面源码分析如何实现上面两件事情。

结构

createInjector -> createInternalInjector return: instanceInjector

所以 createInjector() 返回的是 instanceInjector，结构如下：

rush:js;"> { invoke: invoke,instantiate: instantiate,get: getService,annotate: annotate,has: function(name) { return providerCache.hasOwnProperty(name + providerSuffix) || cache.hasOwnProperty(name); } }

源码分析

rush:js;"> function createInjector(modulesToLoad,strictDi) { strictDi = (strictDi === true); var INSTANTIATING = {},providerSuffix = 'Provider',path = [],loadedModules = new HashMap([],true),// 预先配置$provide,供loadModules中调用注册service等 providerCache = { $provide: { provider: supportObject(provider),factory: supportObject(factory),service: supportObject(service),value: supportObject(value),constant: supportObject(constant),decorator: decorator } },// providerInjector,instanceInjector 两个注入器 // instanceInjector对外提供service等注入，providerInjector对内提供provider获取 providerInjector = (providerCache.$injector = createInternalInjector(providerCache,function() { throw $injectorminerr('unpr',"UnkNown provider: {0}",path.join(' <- ')); },strictDi)),instanceCache = {},instanceInjector = (instanceCache.$injector = createInternalInjector(instanceCache,function(servicename) { var provider = providerInjector.get(servicename + providerSuffix); return instanceInjector.invoke(provider.$get,provider,undefined,servicename); },strictDi));

// 加载模块
forEach(loadModules(modulesToLoad),function(fn) { instanceInjector.invoke(fn || noop); });

return instanceInjector;
}

rush:js;"> $provide: { provider: supportObject(provider),decorator: decorator }

用于包装方法，包装前的方法接受两个参数 (key,value)，经过包装后的方法能支持传入object参数，即多个 key -> value。

rush:js;"> function supportObject(delegate) { return function(key,value) { if (isObject(key)) { forEach(key,reverseParams(delegate)); } else { return delegate(key,value); } }; }

回顾下provider、service 和 factory的使用方式

rush:js;"> app.factory('serviceName',function(){ return { getName: function(){},setName: function(){} } });

app.service('serviceName',function(){
this.getName = function() {}

this.setName = function() {}
});

app.provider('serviceName',function($httpProvider){
// 注入$httpProvider
this.$get = function() {
return {
getName: function(){},setName: function(){}
};
}
});

app.provider('serviceName',{
$get: function () {}
});
function provider(name,provider_) {
assertNotHasOwnProperty(name,'service');
// 当provider是fn或者array时可以将其他provider注入到参数
// 因为providerInjector.instantiate(provider)时可以传入依赖的其他provider
// 这也是provider与service,factory方法不一样的地方
if (isFunction(provider) || isArray(provider)) {
provider = providerInjector.instantiate(provider);
}
if (!provider_.$get) {
throw $injectorminerr('pget',"Provider '{0}' must define $get factory method.",name);
}
return providerCache[name + providerSuffix] = provider_;
}

function factory(name,factoryFn) { return provider(name,{ $get: factoryFn }); }

function service(name,constructor) {
return factory(name,['$injector',function($injector) {
return $injector.instantiate(constructor);
}]);
}

function value(name,val) { return factory(name,valueFn(val)); }

最终汇总到provider的实现，将provider缓存到providerCache，供调用

跟其他不一样的就是constant的实现，分别保存到providerCache和instanceCache中，这样在定义provider还是在定义service是都能注入。

rush:js;"> function constant(name,value) { assertNotHasOwnProperty(name,'constant'); providerCache[name] = value; instanceCache[name] = value; }

rush:js;"> function runInvokeQueue(queue) { var i,ii; for(i = 0,ii = queue.length; i < ii; i++) { var invokeArgs = queue[i],provider = providerInjector.get(invokeArgs[0]); // 存入queue的如格式[$provide,factory,arguments] // 经过替换，$provide.factory.apply($provide,arguments); // 就是调用$provid的factory，service等 provider[invokeArgs[1]].apply(provider,invokeArgs[2]); } }

示例:

rush:js;"> module.config(function($provide) { $provide.decorator('Mail',function($delegate) { $delegate.addCC = function(cc) { this.cc.push(cc); }; return $delegate; }); })

使用示例看出，传入的参数$delegate是原先的service实例，需要在该实例上添加方法都可以，即所谓的装饰器

源码:

rush:js;"> function decorator(serviceName,decorFn) { var origProvider = providerInjector.get(serviceName + providerSuffix),orig$get = origProvider.$get;

origProvider.$get = function() {
// 通过上面获取的provider生成需要的service实例，再以$delegate注入到参数列表
var origInstance = instanceInjector.invoke(orig$get,origProvider);
return instanceInjector.invoke(decorFn,null,{$delegate: origInstance});
};
}

3. createInternalInjector

// 从cache中获取，没有的话调用factory进行创建,具体看getService解析

rush:js;"> function createInternalInjector(cache,factory) {

function getService(serviceName) {
}

function invoke(fn,self,locals,serviceName){
}

function instantiate(Type,serviceName) {
}

return {
// 执行fn，具有参数注入功能
invoke: invoke,// 实例化fn,可以参数注入
instantiate: instantiate,// 获取provider或者service
get: getService,// 获取方法的参数列表，供注入使用
annotate: annotate,// 确认是否含有provider或service
has: function(name) {
return providerCache.hasOwnProperty(name + providerSuffix) || cache.hasOwnProperty(name);
}
};
}

获取fn的参数列表

['a','b','c']

// type2
['a',fn] -> ['a','b']

// type3
function fn () {}
fn.$inject = ['a','c']
-> ['a','c']

源码:

if (typeof fn === 'function') {
if (!($inject = fn.$inject)) {
$inject = [];
if (fn.length) {
// 严格模式下或抛错
if (strictDi) {
if (!isString(name) || !name) {
name = fn.name || anonFn(fn);
}
throw $injectorMinErr('strictdi','{0} is not using explicit annotation and cannot be invoked in strict mode',name);
}
// 将注释去掉
fnText = fn.toString().replace(STRIP_COMMENTS,'');
// 将参数全部选出fn(a,c,d) -> 'a,d'
argDecl = fnText.match(FN_ARGS);
// 分割成array
forEach(argDecl[1].split(FN_ARG_SPLIT),function(arg){
arg.replace(FN_ARG,function(all,underscore,name){
$inject.push(name);
});
});
}
fn.$inject = $inject;
}
} else if (isArray(fn)) {
last = fn.length - 1;
assertArgFn(fn[last],'fn');
$inject = fn.slice(0,last);
} else {
assertArgFn(fn,'fn',true);
}
return $inject;
}

rush:js;"> // 当cache中没有该service时，进入else,先cache[serviceName] = INSTANTIATING 做一个标记 // 因为接下来调用factory(serviceName)，其实是一个递归调用 // function(servicename) { // var provider = providerInjector.get(servicename + providerSuffix); // return instanceInjector.invoke(provider.$get,servicename); // } // instanceInjector.invoke(provider.$get 时会将需要注入的参数get出来然后注入 // 因此做上标记后就可以判断是否有循环依赖 function getService(serviceName) { if (cache.hasOwnProperty(serviceName)) { if (cache[serviceName] === INSTANTIATING) { throw $injectorminerr('cdep','Circular dependency found: {0}',serviceName + ' <- ' + path.join(' <- ')); } return cache[serviceName]; } else { try { path.unshift(serviceName); cache[serviceName] = INSTANTIATING; return cache[serviceName] = factory(serviceName); } catch (err) { if (cache[serviceName] === INSTANTIATING) { delete cache[serviceName]; } throw err; } finally { path.shift(); } } }

rush:js;"> function invoke(fn,serviceName){ if (typeof locals === 'string') { serviceName = locals; locals = null; }

var args = [],// 获取参数列表
$inject = annotate(fn,serviceName),length,i,key;

for(i = 0,length = $inject.length; i < length; i++) {
key = $inject[i];
if (typeof key !== 'string') {
throw $injectorminerr('itkn','Incorrect injection token! Expected service name as string,got {0}',key);
}
// locals优先
args.push(
locals && locals.hasOwnProperty(key)
? locals[key]
: getService(key)
);
}
if (isArray(fn)) {
fn = fn[length];
}

return fn.apply(self,args);
}

rush:js;"> function instantiate(Type,serviceName) { var Constructor = function() {},instance,returnedValue;

// 当type为array时，获取最后的参数如：['$window',function($win){}]
Constructor.prototype = (isArray(Type) ? Type[Type.length - 1] : Type).prototype;
instance = new Constructor();
// 调用invoke执行Type方法
returnedValue = invoke(Type,serviceName);

return isObject(returnedValue) || isFunction(returnedValue) ? returnedValue : instance;
}

instantiate 的作用是用来实例化Type的，在实例化的过程中可以自动传入参数到构造函数。

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