摘要：因為我們正好要使用，此時我們就可以用的服務來監聽了當然，我們不能忘了清空訂閱最后一步就是在有返回的時候調用表單的現在我們可以在組件里顯示提醒了

原文：Connect Angular Forms to @ngrx/store

這篇文章中，我們將要討論如何用ngrx/effects連接Angular表單和ngrx/store

我們最終的結果是這樣的

ew-story0.component.ts

@Component({
  selector: "new-story-form",
  template: `
    

       ...controls
    
    
Success!
    
{{error}}
})
class NewStoryFormComponent {...}

方便起見，我們會寫一個簡單的reducer來組織管理我們應用里的所有的表單

狀態（the state）將由一個用ID作為key，表格數據作為value的簡單對象構成

舉個例子

connect-form.reducer.ts

const initialState = {
  newStory: {
    title: "",
    description: ""
  },
  contactUs: {
    email: "",
    message: ""
  }
}

export function forms(state = initialState, action) {
}

我們先構建一個action——UPDATE_FORM。這個action由兩個key：path和value組成

connect-form1.reducer.ts

store.dispatch({
  type: UPDATE_FORM,
  payload: {
    path: "newStory",
    value: formValue
  }
});

然后這個reducer將負責更新state

connect-form2.reducer.ts

export function forms(state = initialState, action) {
  if(action.type === UPDATE_FORM) { 
                       // newStory:           formValue
    return { ...state, [action.payload.path]: action.payload.value }
  }
}

我們想要基于state更新表單，所以我們需要path作為輸入，然后取出store中正確的片段

connect-form.directive.ts

@Directive({
  selector: "[connectForm]"
})
export class ConnectFormDirective {
  @Input("connectForm") path: string;

  constructor(private formGroupDirective: FormGroupDirective,
    private store: Store ) {
      
    ngOnInit() {
      // Update the form value based on the state
      this.store.select(state => state.forms[this.path]).take(1).subscribe(formValue => {
        this.formGroupDirective.form.patchValue(formValue);
      });
    }
  }
}

我們抓取表單directive實例然后從store里更新表單數據

當表單數據改變時我們也需要更新表單狀態。我們可以通過訂閱（subscribe）這個valueChanges的可觀察對象（observable）然后調度（dispatch）這個UPDATE_FORM的action來獲取值

connect-form1.directive.ts

this.formChange = this.formGroupDirective.form.valueChanges
  .subscribe(value => {
    this.store.dispatch({
      type: UPDATE_FORM,
      payload: {
        value,
        path: this.path, // newStory
      }
    });
})

這就是表單和State同步所要做的全部工作了

有兩件事我們要在這個部分完成

基于HTTP響應返回來顯示通知給用戶——我們需要保證通知直接傳給組件并且不儲存信息在store里

有兩點原因

通常，沒有其他的組件需要這個信息

我們不想每次都重置store

當提交成功時重置表單

我們將讓Angular盡其所能，處理好前端表單校驗并重置表單

成功的Action包含表單的path屬性所以我們可以知道到底哪個表單需要重置，同時什么時候需要去使用（emit）這個成功的事件

connect-form2.directive.ts

const FORM_SUBMIT_SUCCESS = "FORM_SUBMIT_SUCCESS";
const FORM_SUBMIT_ERROR = "FORM_SUBMIT_ERROR";
const UPDATE_FORM = "UPDATE_FORM";

export const formSuccessAction = path => ({
  type: FORM_SUBMIT_SUCCESS,
  payload: {
    path
  }
});

同成功的action一樣，因為有path的存在，我們也知道何時去使用（emit）錯誤異常 的事件

connect-form3.directive.ts

export const formErrorAction = ( path, error ) => ({
  type: FORM_SUBMIT_ERROR,
  payload: {
    path,
    error
  }
});

我們需要創建 成功 和 錯誤異常 的輸出 然后 監聽 FORM_SUBMIT_ERROR 和 FORM_SUBMIT_SUCCESS 的 action。

因為我們正好要使用 ngrx/effects ，此時我們就可以用 Action 的服務（service）來監聽actions了

connect-form3.directive.ts

@Directive({
  selector: "[connectForm]"
})
export class ConnectFormDirective {
  @Input("connectForm") path : string;
  @Input() debounce : number = 300;
  @Output() error = new EventEmitter();
  @Output() success = new EventEmitter();
  formChange : Subscription;
  formSuccess : Subscription;
  formError : Subscription;

  constructor( private formGroupDirective : FormGroupDirective,
               private actions$ : Actions,
               private store : Store ) {
  }

  ngOnInit() {
    this.store.select(state => state.forms[this.path])
      .debounceTime(this.debounce)
      .take(1).subscribe(val => {
      this.formGroupDirective.form.patchValue(val);
    });

    this.formChange = this.formGroupDirective.form.valueChanges
      .debounceTime(this.debounce).subscribe(value => {
        this.store.dispatch({
          type: UPDATE_FORM,
          payload: {
            value,
            path: this.path,
          }
        });
      });

    this.formSuccess = this.actions$
      .ofType(FORM_SUBMIT_SUCCESS)
      .filter(( { payload } ) => payload.path === this.path)
      .subscribe(() => {
        this.formGroupDirective.form.reset();
        this.success.emit();
      });

    this.formError = this.actions$
      .ofType(FORM_SUBMIT_ERROR)
      .filter(( { payload } ) => payload.path === this.path)
      .subscribe(( { payload } ) => this.error.emit(payload.error))
  }
}

當然，我們不能忘了清空訂閱

connect-form4.directive.ts

ngOnDestroy() {
  this.formChange.unsubscribe();
  this.formError.unsubscribe();
  this.formSuccess.unsubscribe();
}

最后一步就是在有返回的時候調用表單的actions

connect-form4.directive.ts

import {
  formErrorAction,
  formSuccessAction
} from "../connect-form.directive";

@Effect() addStory$ = this.actions$
  .ofType(ADD_STORY)
  .switchMap(action =>
    this.storyService.add(action.payload)
    .switchMap(story => (Observable.from([{
      type: "ADD_STORY_SUCCESS"
    }, formSuccessAction("newStory")])))
    .catch(err => (Observable.of(formErrorAction("newStory", err))))
  )

 

現在我們可以在組件里顯示提醒了

ew-story.component.ts

 @Component({
  selector: "new-story-form",
  template: `
    

       ...controls
      Submit
    
    
Success!
    
{{error}}
  `
})
class NewStoryFormComponent {

  constructor(private store: Store ) {}

  onError(error) {
    this.error = error;
  }

  onSuccess() {
    this.success = true;
  }

  submit() {
    // You can also take the payload from the form state in your effect 
    // with the withLatestFrom observable
    this.store.dispatch({
      type: ADD_STORY,
      payload: ...
    })
  }

}