Tokenizing for AoT compilation

问题

I've been having some issues with the inconsistencies between the JIT and AoT compilers. The most recent error that has stumped me was Error: Can't resolve all parameters for IndexedDBCache. IndexedDBCache is a service that depends on a string parameter:

Please note this issue also arises when I remove the 'protected' property!

// indexeddb-cache.ts
import { Injectable } from '@angular/core';

@Injectable()
export class IndexedDBCache {
  constructor(protected databaseName : string) {}
}

I'm using a factory to provide versions of the service:

// test-api.cache.factory.ts
import { IndexedDBCache } from '../indexeddb-cache/indexeddb-cache';

export function testIndexedDBCacheFactory() { return new IndexedDBCache('test'); }

// test-api.cache.ts
import { InjectionToken, Provider } from '@angular/core';
import { IndexedDBCache } from '../indexeddb-cache/indexeddb-cache';
import { testIndexedDBCacheFactory } from './test-api.cache.factory';

export const testIndexedDBCache = new InjectionToken<IndexedDBCache>('testIndexedDBCache');

export let testIndexedDBCacheProvider : Provider = {
  provide: testIndexedDBCache,
  useFactory: testIndexedDBCacheFactory
};

Note : These files have to be split according to func-in-providers-useFactory and arrow-function-exports - don't ask me why =/

Now the AoT compiler doesn't like this string paramter at all. I've looked into the issue but could only find reference to OpaqueToken (now depricated and replaced by InjectionToken<string>). My code would now read:

// test-api.cache.factory.ts
import { InjectionToken } from '@angular/core';
import { IndexedDBCache } from '../indexeddb-cache/indexeddb-cache';

const testIndexedDBCacheFactoryToken = new InjectionToken<string>('test');
export function testIndexedDBCacheFactory() { return new IndexedDBCache(testIndexedDBCacheFactoryToken); }

Obviously this is not compiling as the constructor would only allow for a string parameter. I don't have enough knowledge about InjectionTokens or the AoT issue at hand to solve this - anyone have a suggestion for a construct that would work?

More context on my code and issue to be found at angular/angular#17295.

---

Things I've tried:

1. Removing the protected access modifier > Exact same error persists
2. Removing the string parameter > Not an option - it defines the service
3. Replacing the string parameter in the factory with an InjectionToken<string> > An InjectionToken is not a suitable parameter

回答1:

There was a misunderstanding of the issue at hand. The classes to be factoried are not services themselves and as such do not need the @Injectable property. More detail to be found at Creating AoT compatible Service Factories

来源：https://stackoverflow.com/questions/44432641/tokenizing-for-aot-compilation