简介
injector是用来做参数自动注入的，例如
function fn ($http, $scope, aService) {
}
ng在运行时会把$http, $scope, aService 自动作为参数传入进行执行。
其实很容易想明白，injector做了两件事
- 缓存那些service，以后作为参数注入
- 分析参数列表，找到需要的参数注入
下面源码分析如何实现上面两件事情。
结构
createInjector -> createInternalInjector return: instanceInjector
所以 createInjector() 返回的是 instanceInjector，结构如下：
{
invoke: invoke,
instantiate: instantiate,
get: getService,
annotate: annotate,
has: function(name) {
return providerCache.hasOwnProperty(name + providerSuffix) || cache.hasOwnProperty(name);
}
}
源码分析
1. createInjector
function createInjector(modulesToLoad, strictDi) {
strictDi = (strictDi === true);
var INSTANTIATING = {},
providerSuffix = 'Provider',
path = [],
loadedModules = new HashMap([], true),
// 预先配置$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;
}
2. $provide
$provide: {
provider: supportObject(provider),
factory: supportObject(factory),
service: supportObject(service),
value: supportObject(value),
constant: supportObject(constant),
decorator: decorator
}
2.1 supportObject
用于包装方法，包装前的方法接受两个参数 (key, value)，经过包装后的方法能支持传入object参数，即多个 key -> value。
function supportObject(delegate) {
return function(key, value) {
if (isObject(key)) {
forEach(key, reverseParams(delegate));
} else {
return delegate(key, value);
}
};
}
2.2 provider
回顾下provider、service 和 factory的使用方式
app.factory('serviceName', function(){
return {
getName: function(){},
setName: function(){}
}
});
app.service('serviceName', function(){
this.getName = function() {}
this.setName = function() {}
});
app.provider('serviceName', function($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 $injector.instantiate(constructor);
}]);
}
function value(name, val) { return factory(name, valueFn(val)); }
最终汇总到provider的实现，将provider缓存到providerCache，供调用
跟其他不一样的就是constant的实现，分别保存到providerCache和instanceCache中，这样在定义provider还是在定义service是都能注入。
function constant(name, value) {
assertNotHasOwnProperty(name, 'constant');
providerCache[name] = value;
instanceCache[name] = value;
}
2.3 回顾 loadModules
function runInvokeQueue(queue) {
var i, ii;
for(i = 0, ii = queue.length; i < ii; i++) {
var invokeArgs = queue[i],
provider = providerInjector.get(invokeArgs[0]);
// 存入queue的如格式[$provide, factory, arguments]
// 经过替换，$provide.factory.apply($provide, arguments);
// 就是调用$provid的factory，service等
provider[invokeArgs[1]].apply(provider, invokeArgs[2]);
}
}
2.4 decorator
示例:
module.config(function($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:
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
3.1 整体结构
// 从cache中获取，没有的话调用factory进行创建,具体看getService解析
function createInternalInjector(cache, factory) {
function getService(serviceName) {
}
function invoke(fn, self, locals, serviceName){
}
function instantiate(Type, locals, 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);
}
};
}
3.2 annotate
获取fn的参数列表
// type1
function fn (a, b, c) -> ['a', 'b', 'c']
// type2
['a', 'b', fn] -> ['a', 'b']
// type3
function fn () {}
fn.$inject = ['a', 'c']
-> ['a', 'c']
源码:
function annotate(fn, strictDi, name) {
var $inject,
fnText,
argDecl,
last;
if (typeof fn === 'function') {
if (!($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,b,c,d) -> 'a,b,c,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 $inject;
}
3.3 getService
// 当cache中没有该service时，进入else, 先cache[serviceName] = INSTANTIATING 做一个标记
// 因为接下来调用factory(serviceName)，其实是一个递归调用
// function(servicename) {
// var provider = providerInjector.get(servicename + providerSuffix);
// return instanceInjector.invoke(provider.$get, provider, undefined, 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();
}
}
}
3.4 invoke
function invoke(fn, self, locals, serviceName){
if (typeof locals === 'string') {
serviceName = locals;
locals = null;
}
var args = [],
// 获取参数列表
$inject = annotate(fn, strictDi, serviceName),
length, i,
key;
for(i = 0, length = $inject.length; i < length; i++) {
key = $inject[i];
if (typeof key !== 'string') {
throw $injectorMinErr('itkn',
'Incorrect injection token! Expected service name as string, got {0}', key);
}
// locals优先
args.push(
locals && locals.hasOwnProperty(key)
"color: #993300">3.5 instantiate
function instantiate(Type, locals, serviceName) {
var Constructor = function() {},
instance, returnedValue;
// 当type为array时，获取最后的参数如：['$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, instance, locals, 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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