`Angular Platform` 创建相关

Angular Platform :

• createPlatformFactory
• createPlatform

createPlatformFactory

工厂函数 parentPlatformFactory 调用结束后 （=null)， 开始组合所有 providers ，然后创建 Root Injector, 最后调用 createPlatform(...) 创建出 PlatformRef 实例.

export function createPlatformFactory(
    parentPlatformFactory: ((extraProviders?: StaticProvider[]) => PlatformRef)|null, name: string,
    providers: StaticProvider[] = []): (extraProviders?: StaticProvider[]) => PlatformRef {
  const desc = `Platform: ${name}`;
  const marker = new InjectionToken(desc);
  return (extraProviders: StaticProvider[] = []) => {
    let platform = getPlatform();
    if (!platform || platform.injector.get(ALLOW_MULTIPLE_PLATFORMS, false)) {
      if (parentPlatformFactory) {
        parentPlatformFactory(
            providers.concat(extraProviders).concat({provide: marker, useValue: true}));
      } else {
        const injectedProviders: StaticProvider[] =
            providers.concat(extraProviders).concat({provide: marker, useValue: true}, {
              provide: INJECTOR_SCOPE,
              useValue: 'platform'
            });
        createPlatform(Injector.create({providers: injectedProviders, name: desc}));
      }
    }
    return assertPlatform(marker);
  };
}

createPlatform

通过 Root Injector 创建和取回 PlatformRef, 而这个 PlatformRef 是在之前工厂里面的 providers 注册的，这里呢，不管那么多用就完了，哈哈哈。

漏了点东西， PLATFORM_INITIALIZER, 这货的 multi 为 true， 所以 injector.get(PLATFORM_INITIALIZER, null) 如果值不是 null 那就只能是个数组了。

如果 PLATFORM_INITIALIZER 取回来是个数组，那就逐个遍历调用那些通过 PLATFORM_INITIALIZER 定义的工厂函数，可以看做是平台初始化，当一切都搞定后，就返回 _platform 平台对象。

export function createPlatform(injector: Injector): PlatformRef {
  if (_platform && !_platform.destroyed &&
      !_platform.injector.get(ALLOW_MULTIPLE_PLATFORMS, false)) {
    throw new Error(
        'There can be only one platform. Destroy the previous one to create a new one.');
  }
  publishDefaultGlobalUtils();
  _platform = injector.get(PlatformRef);
  const inits = injector.get(PLATFORM_INITIALIZER, null);
  if (inits) inits.forEach((init: any) => init());
  return _platform;
}