摘要：上一篇說到了平臺實例在初始化的時候會創建根注入器那現在就一起看看注入器是如何創建的又是如何工作的所有引用的代碼都被簡化了創建注入器程序初始化時調用的創建根注入器的靜態方法調用此方法會返回一個類型的實例也就是注入器類注入器的構造函數在初始化過
上一篇說到了平臺實例在初始化的時候會創建根注入器,那現在就一起看看注入器是如何創建的,又是如何工作的.(所有引用的代碼都被簡化了)
創建注入器
程序初始化時調用的創建根注入器的靜態方法:
abstract class Injector{
static create(options: StaticProvider[]|{providers: StaticProvider[], parent?: Injector, name?: string},parent?: Injector): Injector {
if (Array.isArray(options)) {
return new StaticInjector(options, parent);
} else {
return new StaticInjector(options.providers, options.parent, options.name || null);
}
}
調用此方法會返回一個StaticInjector類型的實例(也就是注入器).
StaticInjector類
export class StaticInjector implements Injector {
readonly parent: Injector;
readonly source: string|null;
private _records: Map;
constructor(providers: StaticProvider[], parent: Injector = NULL_INJECTOR, source: string|null = null) {
this.parent = parent;
this.source = source;
const records = this._records = new Map();
records.set(Injector, {token: Injector, fn: IDENT, deps: EMPTY, value: this, useNew: false});
records.set(INJECTOR, {token: INJECTOR, fn: IDENT, deps: EMPTY, value: this, useNew: false});
recursivelyProcessProviders(records, providers);
}
}
注入器的構造函數在初始化過程中的操作:
設置當前注入器的父注入器
設置注入器的源
新建注冊表(_records屬性,是一個Map類型)
將參數providers全部添加到注冊表中
向注冊表中添加服務調用了recursivelyProcessProviders函數
const EMPTY = [];
const MULTI_PROVIDER_FN = function (): any[] { return Array.prototype.slice.call(arguments) };
function recursivelyProcessProviders(records: Map, provider: StaticProvider) {
if (provider instanceof Array) {
for (let i = 0; i < provider.length; i++) {
recursivelyProcessProviders(records, provider[i]);
}
} else (provider && typeof provider === "object" && provider.provide) {
let token = resolveForwardRef(provider.provide);// 方法`resolveForwardRef`的作用可能是向前兼容,可以忽略
const resolvedProvider = resolveProvider(provider);
if (provider.multi === true) {
let multiProvider: Record | undefined = records.get(token);
if (multiProvider) {
if (multiProvider.fn !== MULTI_PROVIDER_FN) {
throw multiProviderMixError(token);
}
} else {
records.set(token, multiProvider = {
token: provider.provide,
deps: [],
useNew: false, // 這個值在后面獲取依賴實例的時候會用到,當做判斷條件
fn: MULTI_PROVIDER_FN,
value: EMPTY // 這個值在后面獲取依賴實例的時候會用到,當做判斷條件
});
}
token = provider;
multiProvider.deps.push({ token, options: OptionFlags.Default });
}
records.set(token, resolvedProvider);
}
}
recursivelyProcessProviders函數具體的執行過程:
如果provider是個數組,那就遍歷后依次調用此方法.
如果provider是個對象:
1 獲取token
let token = resolveForwardRef(provider.provide);
2 調用resolveProvider方法處理服務中可能出現的屬性和依賴,返回一個Record對象,此對象會作為token的值
function resolveProvider(provider: SupportedProvider): Record {
const deps = computeDeps(provider);
let fn: Function = function (value) { return value };
let value: any = [];
// useUew用來標識是否需要 new
let useNew: boolean = false;
let provide = resolveForwardRef(provider.provide);
if (USE_VALUE in provider) {
value = provider.useValue;
} else if (provider.useFactory) {
fn = provider.useFactory;
} else if (provider.useExisting) {
//do nothing
} else if (provider.useClass) {
useNew = true;
fn = resolveForwardRef(provider.useClass);
} else if (typeof provide == "function") {
useNew = true;
fn = provide;
} else {
throw staticError("StaticProvider does not have [useValue|useFactory|useExisting|useClass] or [provide] is not newable", provider);
}
return { deps, fn, useNew, value }; // provider中不同的屬性會返回包含不同值的對象
}
這個方法會先調用computeDeps函數處理服務需要的依賴,它將useExisting類型的服務也轉換成deps,最后返回[{ token, OptionFlags }]形式的數組(OptionFlags是枚舉常量)
function computeDeps(provider: StaticProvider): DependencyRecord[] {
let deps: DependencyRecord[] = EMPTY;
const providerDeps: any[] = provider.deps;
if (providerDeps && providerDeps.length) {
deps = [];
for (let i = 0; i < providerDeps.length; i++) {
let options = OptionFlags.Default;
let token = resolveForwardRef(providerDeps[i]);
deps.push({ token, options });
}
} else if ((provider as ExistingProvider).useExisting) {
const token = resolveForwardRef((provider as ExistingProvider).useExisting);
deps = [{ token, options: OptionFlags.Default }];
}
return deps;
}
resolveProvider函數最終返回的Record對象有一個缺省值:
{
deps:[], // 包含依賴時 [{ token, options },{ token, options }]
fn:function(value) { return value },
useNew:false,
value:[]
}
執行過程中會根據provider不同的屬性修改Record對象的變量為不同的值:
useValue : 修改value為useValue的值
useFactory : 修改fn為對應的函數
useClass 或 typeof provide == "function"(令牌為一個函數時) : 修改fn為對應的函數,并設置useNew為true
useExisting : 不做修改,直接使用默認值
3 如果是多處理服務(multi:ture)且為首次注冊,那么在注冊表中額外注冊一個占位的Record
records.set(token, multiProvider = {
token: provider.provide,
deps: [],
useNew: false,
fn: MULTI_PROVIDER_FN,
value: EMPTY
});
4 非多處理服務以token為鍵,多處理服務以provider對象為鍵,返回的Record對象為值,存入注冊表records中
從注入器中獲取實例
服務注冊完,下一步就是怎么從注入器中獲取服務的實例了,這會調用StaticInjector的get方法
export class StaticInjector implements Injector {
get(token: any, notFoundValue?: any, flags: InjectFlags = InjectFlags.Default): any {
// 獲取token對應的record
const record = this._records.get(token);
return resolveToken(token, record, this._records, this.parent, notFoundValue, flags);
}
get方法調用了resolveToken函數,這個函數會返回token對應的實例(就是被注入的對象)
const EMPTY = [];
const CIRCULAR = IDENT;
const IDENT = function (value: T): T { return value };
function resolveToken(token: any, record: Record | undefined, records: Map, parent: Injector,
notFoundValue: any, flags: InjectFlags): any {
let value;
if (record && !(flags & InjectFlags.SkipSelf)) {
value = record.value;
if (value == CIRCULAR) {
throw Error(NO_NEW_LINE + "Circular dependency");
} else if (value === EMPTY) {
record.value = CIRCULAR;
let obj = undefined;
let useNew = record.useNew;
let fn = record.fn;
let depRecords = record.deps;
let deps = EMPTY;
if (depRecords.length) {
deps = [];
for (let i = 0; i < depRecords.length; i++) {
const depRecord: DependencyRecord = depRecords[i];
const options = depRecord.options;
const childRecord = options & OptionFlags.CheckSelf ? records.get(depRecord.token) : undefined;
deps.push(tryResolveToken(
depRecord.token,
childRecord,
records,
!childRecord && !(options & OptionFlags.CheckParent) ? NULL_INJECTOR : parent,
options & OptionFlags.Optional ? null : Injector.THROW_IF_NOT_FOUND,
InjectFlags.Default));
}
}
record.value = value = useNew ? new (fn as any)(...deps) : fn.apply(obj, deps);
}
} else if (!(flags & InjectFlags.Self)) {
value = parent.get(token, notFoundValue, InjectFlags.Default);
}
return value;
}
函數中會先判斷當前請求的token是否存在,如果不存在則去當前注入器的父注入器中尋找,如果存在:
獲取token對應的record
判斷record.value是否為[](非useValue類型的服務/多處理服務的默認值是[]):
ture : 非useValue類型的服務/多處理服務或此服務沒有被創建過
查看是否包含依賴,包含則優先創建依賴的實例,也是調用這個函數
根據record.fn創建當前token對應的實例并更新record.value(這里需要根據record.useNew來判斷是否需要用new來實例化,比如useFactory類型就不需要new,而useExisting更是直接返回了deps)
返回這個值
false : useValue類型的服務或此服務已經被創建過
直接返回這個值
