角度和去抖动

2020/10/28 10:03 · javascript ·  · 0评论

在AngularJS中,我可以通过使用ng-model选项来消除模型的反跳。

ng-model-options="{ debounce: 1000 }"

如何在Angular中对模型进行反跳?

我试图在文档中搜索反跳,但找不到任何东西。

https://angular.io/search/#stq=debounce&stp=1

一种解决方案是编写我自己的防抖动功​​能,例如:

import {Component, Template, bootstrap} from 'angular2/angular2';

// Annotation section
@Component({
  selector: 'my-app'
})
@Template({
  url: 'app.html'
})
// Component controller
class MyAppComponent {
  constructor() {
    this.firstName = 'Name';
  }
    
  changed($event, el){
    console.log("changes", this.name, el.value);
    this.name = el.value;
  }

  firstNameChanged($event, first){
    if (this.timeoutId) window.clearTimeout(this.timeoutID);
    this.timeoutID = window.setTimeout(() => {
        this.firstName = first.value;
    }, 250)
  }
    
}
bootstrap(MyAppComponent);

和我的HTML

<input type=text [value]="firstName" #first (keyup)="firstNameChanged($event, first)">

但是我正在寻找一个内置函数,Angular中有一个吗?

针对RC.5更新

使用Angular 2,我们可以debounceTime()在窗体控件的valueChanges可观察对象使用RxJS运算符进行反跳

import {Component}   from '@angular/core';
import {FormControl} from '@angular/forms';
import {Observable}  from 'rxjs/Observable';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/throttleTime';
import 'rxjs/add/observable/fromEvent';

@Component({
  selector: 'my-app',
  template: `<input type=text [value]="firstName" [formControl]="firstNameControl">
    <br>{{firstName}}`
})
export class AppComponent {
  firstName        = 'Name';
  firstNameControl = new FormControl();
  formCtrlSub: Subscription;
  resizeSub:   Subscription;
  ngOnInit() {
    // debounce keystroke events
    this.formCtrlSub = this.firstNameControl.valueChanges
      .debounceTime(1000)
      .subscribe(newValue => this.firstName = newValue);
    // throttle resize events
    this.resizeSub = Observable.fromEvent(window, 'resize')
      .throttleTime(200)
      .subscribe(e => {
        console.log('resize event', e);
        this.firstName += '*';  // change something to show it worked
      });
  }
  ngDoCheck() { console.log('change detection'); }
  ngOnDestroy() {
    this.formCtrlSub.unsubscribe();
    this.resizeSub  .unsubscribe();
  }
} 

Plunker

上面的代码还包括一个如何限制窗口调整大小事件的示例,如@albanx在下面的注释中所要求的。


尽管上面的代码可能是这样做的Angular方法,但效率不高。每次击键和每次调整大小事件(即使它们被去抖和抑制)都将导致更改检测运行。换句话说,去抖动和节流不影响更改检测运行的频率(我找到了Tobias BoschGitHub评论对此进行了确认。)您可以在运行插入器时看到此消息,并ngDoCheck()在键入输入框或调整窗口大小时看到被调用了多少次(使用蓝色的“ x”按钮在单独的窗口中运行插件,以查看调整大小事件。)

一种更有效的技术是在Angular的“区域”之外,根据事件自己创建RxJS Observable。这样,每次事件触发时都不会调用更改检测。然后,在您的订阅回调方法中,手动触发更改检测-即,您控制何时调用更改检测:

import {Component, NgZone, ChangeDetectorRef, ApplicationRef, 
        ViewChild, ElementRef} from '@angular/core';
import {Observable} from 'rxjs/Observable';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/throttleTime';
import 'rxjs/add/observable/fromEvent';

@Component({
  selector: 'my-app',
  template: `<input #input type=text [value]="firstName">
    <br>{{firstName}}`
})
export class AppComponent {
  firstName = 'Name';
  keyupSub:  Subscription;
  resizeSub: Subscription;
  @ViewChild('input') inputElRef: ElementRef;
  constructor(private ngzone: NgZone, private cdref: ChangeDetectorRef,
    private appref: ApplicationRef) {}
  ngAfterViewInit() {
    this.ngzone.runOutsideAngular( () => {
      this.keyupSub = Observable.fromEvent(this.inputElRef.nativeElement, 'keyup')
        .debounceTime(1000)
        .subscribe(keyboardEvent => {
          this.firstName = keyboardEvent.target.value;
          this.cdref.detectChanges();
        });
      this.resizeSub = Observable.fromEvent(window, 'resize')
        .throttleTime(200)
        .subscribe(e => {
          console.log('resize event', e);
          this.firstName += '*';  // change something to show it worked
          this.cdref.detectChanges();
        });
    });
  }
  ngDoCheck() { console.log('cd'); }
  ngOnDestroy() {
    this.keyupSub .unsubscribe();
    this.resizeSub.unsubscribe();
  }
} 

Plunker

我使用ngAfterViewInit()而不是ngOnInit()确保inputElRef已定义。

detectChanges()将对此组件及其子组件运行更改检测。如果您希望从根组件运行更改检测(即运行完整的更改检测检查),请ApplicationRef.tick()改用。(我ApplicationRef.tick()在插件的注释中打了个电话。)请注意,tick()将导致ngDoCheck()被调用。

如果您不想处理@angular/forms,则可以只使用Subject带有更改绑定的RxJS

view.component.html

<input [ngModel]='model' (ngModelChange)='changed($event)' />

view.component.ts

import { Subject } from 'rxjs/Subject';
import { Component }   from '@angular/core';
import 'rxjs/add/operator/debounceTime';

export class ViewComponent {
    model: string;
    modelChanged: Subject<string> = new Subject<string>();

    constructor() {
        this.modelChanged
            .debounceTime(300) // wait 300ms after the last event before emitting last event
            .distinctUntilChanged() // only emit if value is different from previous value
            .subscribe(model => this.model = model);
    }

    changed(text: string) {
        this.modelChanged.next(text);
    }
}

这确实会触发更改检测。对于不触发更改检测的方法,请查看Mark的答案。


更新资料

.pipe(debounceTime(300), distinctUntilChanged()) rxjs 6需要它。

例:

   constructor() {
        this.modelChanged.pipe(
            debounceTime(300), 
            distinctUntilChanged())
            .subscribe(model => this.model = model);
    }

由于主题较旧,因此大多数答案不适用于Angular 6/7/8/9/10和/或使用其他库。

因此,这是使用RxJS的Angular 6+的简短解决方案。

首先导入必要的内容:

import { Component, OnInit, OnDestroy } from '@angular/core';
import { Subject, Subscription } from 'rxjs';
import { debounceTime, distinctUntilChanged } from 'rxjs/operators';

初始化ngOnInit

export class MyComponent implements OnInit, OnDestroy {
  public notesText: string;
  private notesModelChanged: Subject<string> = new Subject<string>();
  private notesModelChangeSubscription: Subscription

  constructor() { }

  ngOnInit() {
    this.notesModelChangeSubscription = this.notesModelChanged
      .pipe(
        debounceTime(2000),
        distinctUntilChanged()
      )
      .subscribe(newText => {
        this.notesText = newText;
        console.log(newText);
      });
  }

  ngOnDestroy() {
    this.notesModelChangeSubscription.unsubscribe();
  }
}

使用这种方式:

<input [ngModel]='notesText' (ngModelChange)='notesModelChanged.next($event)' />

PS:对于更复杂,更有效的解决方案,您可能仍然需要检查其他答案。

可以作为指令实施

import { Directive, Input, Output, EventEmitter, OnInit, OnDestroy } from '@angular/core';
import { NgControl } from '@angular/forms';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';
import { Subscription } from 'rxjs';

@Directive({
  selector: '[ngModel][onDebounce]',
})
export class DebounceDirective implements OnInit, OnDestroy {
  @Output()
  public onDebounce = new EventEmitter<any>();

  @Input('debounce')
  public debounceTime: number = 300;

  private isFirstChange: boolean = true;
  private subscription: Subscription;

  constructor(public model: NgControl) {
  }

  ngOnInit() {
    this.subscription =
      this.model.valueChanges
        .debounceTime(this.debounceTime)
        .distinctUntilChanged()
        .subscribe(modelValue => {
          if (this.isFirstChange) {
            this.isFirstChange = false;
          } else {
            this.onDebounce.emit(modelValue);
          }
        });
  }

  ngOnDestroy() {
    this.subscription.unsubscribe();
  }

}

用起来像

<input [(ngModel)]="value" (onDebounce)="doSomethingWhenModelIsChanged($event)">

成分样本

import { Component } from "@angular/core";

@Component({
  selector: 'app-sample',
  template: `
<input[(ngModel)]="value" (onDebounce)="doSomethingWhenModelIsChanged($event)">
<input[(ngModel)]="value" (onDebounce)="asyncDoSomethingWhenModelIsChanged($event)">
`
})
export class SampleComponent {
  value: string;

  doSomethingWhenModelIsChanged(value: string): void {
    console.log({ value });
  }

  async asyncDoSomethingWhenModelIsChanged(value: string): Promise<void> {
    return new Promise<void>(resolve => {
      setTimeout(() => {
        console.log('async', { value });
        resolve();
      }, 1000);
    });
  }
} 

不能像在angular1中那样直接访问,但是您可以轻松地使用NgFormControl和RxJS observables:

<input type="text" [ngFormControl]="term"/>

this.items = this.term.valueChanges
  .debounceTime(400)
  .distinctUntilChanged()
  .switchMap(term => this.wikipediaService.search(term));

该博客文章对此进行了清晰的解释:http :
//blog.thoughtram.io/angular/2016/01/06/taking-advantage-of-observables-in-angular2.html

这是自动完成功能,但它适用于所有情况。

您可以创建一个RxJS(v.6)Observable,执行您喜欢的任何操作。

view.component.html

<input type="text" (input)="onSearchChange($event.target.value)" />

view.component.ts

import { Observable } from 'rxjs';
import { debounceTime, distinctUntilChanged } from 'rxjs/operators';

export class ViewComponent {
    searchChangeObserver;

  onSearchChange(searchValue: string) {

    if (!this.searchChangeObserver) {
      Observable.create(observer => {
        this.searchChangeObserver = observer;
      }).pipe(debounceTime(300)) // wait 300ms after the last event before emitting last event
        .pipe(distinctUntilChanged()) // only emit if value is different from previous value
        .subscribe(console.log);
    }

    this.searchChangeObserver.next(searchValue);
  }  


}

对于使用lodash的任何人来说,去抖动任何功能都非常容易

changed = _.debounce(function() {
    console.log("name changed!");
}, 400);

然后将这样的东西扔到您的模板中:

<(input)="changed($event.target.value)" />

直接在事件函数中使用初始化订户的解决方案:

import {Subject} from 'rxjs';
import {debounceTime, distinctUntilChanged} from 'rxjs/operators';

class MyAppComponent {
    searchTermChanged: Subject<string> = new Subject<string>();

    constructor() {
    }

    onFind(event: any) {
        if (this.searchTermChanged.observers.length === 0) {
            this.searchTermChanged.pipe(debounceTime(1000), distinctUntilChanged())
                .subscribe(term => {
                    // your code here
                    console.log(term);
                });
        }
        this.searchTermChanged.next(event);
    }
}

和html:

<input type="text" (input)="onFind($event.target.value)">

我通过编写一个防抖动装饰器解决了这一问题。可以通过将@debounceAccessor应用于属性的set访问器来解决所描述的问题。

我还为方法提供了一个额外的防抖动装饰器,该装饰器在其他场合也很有用。

这使得去抖动属性或方法非常容易。该参数是防抖动应该持续的毫秒数,在下面的示例中为100 ms。

@debounceAccessor(100)
set myProperty(value) {
  this._myProperty = value;
}


@debounceMethod(100)
myMethod (a, b, c) {
  let d = a + b + c;
  return d;
}

这是装饰器的代码:

function debounceMethod(ms: number, applyAfterDebounceDelay = false) {

  let timeoutId;

  return function (target: Object, propName: string, descriptor: TypedPropertyDescriptor<any>) {
    let originalMethod = descriptor.value;
    descriptor.value = function (...args: any[]) {
      if (timeoutId) return;
      timeoutId = window.setTimeout(() => {
        if (applyAfterDebounceDelay) {
          originalMethod.apply(this, args);
        }
        timeoutId = null;
      }, ms);

      if (!applyAfterDebounceDelay) {
        return originalMethod.apply(this, args);
      }
    }
  }
}

function debounceAccessor (ms: number) {

  let timeoutId;

  return function (target: Object, propName: string, descriptor: TypedPropertyDescriptor<any>) {
    let originalSetter = descriptor.set;
    descriptor.set = function (...args: any[]) {
      if (timeoutId) return;
      timeoutId = window.setTimeout(() => {
        timeoutId = null;
      }, ms);
      return originalSetter.apply(this, args);
    }
  }
}

我为方法装饰器添加了一个附加参数,让您在去抖动延迟之后触发方法。我这样做是为了例如在与鼠标悬停或调整大小事件结合使用时使用它,我希望捕获发生在事件流的末尾。但是,在这种情况下,该方法将不会返回值。

我们可以创建一个[debounce]指令,该指令用一个空的值覆盖ngModel的默认viewToModelUpdate函数。

指令代码

@Directive({ selector: '[debounce]' })
export class MyDebounce implements OnInit {
    @Input() delay: number = 300;

    constructor(private elementRef: ElementRef, private model: NgModel) {
    }

    ngOnInit(): void {
        const eventStream = Observable.fromEvent(this.elementRef.nativeElement, 'keyup')
            .map(() => {
                return this.model.value;
            })
            .debounceTime(this.delay);

        this.model.viewToModelUpdate = () => {};

        eventStream.subscribe(input => {
            this.model.viewModel = input;
            this.model.update.emit(input);
        });
    }
}

如何使用它

<div class="ui input">
  <input debounce [delay]=500 [(ngModel)]="myData" type="text">
</div>

HTML档案:

<input [ngModel]="filterValue"
       (ngModelChange)="filterValue = $event ; search($event)"
        placeholder="Search..."/>

TS文件:

timer = null;
time = 250;
  search(searchStr : string) : void {
    clearTimeout(this.timer);
    this.timer = setTimeout(()=>{
      console.log(searchStr);
    }, time)
  }

一个简单的解决方案是创建可以应用于任何控件的指令。

import { Directive, ElementRef, Input, Renderer, HostListener, Output, EventEmitter } from '@angular/core';
import { NgControl } from '@angular/forms';

@Directive({
    selector: '[ngModel][debounce]',
})
export class Debounce 
{
    @Output() public onDebounce = new EventEmitter<any>();

    @Input('debounce') public debounceTime: number = 500;

    private modelValue = null;

    constructor(public model: NgControl, el: ElementRef, renderer: Renderer){
    }

    ngOnInit(){
        this.modelValue = this.model.value;

        if (!this.modelValue){
            var firstChangeSubs = this.model.valueChanges.subscribe(v =>{
                this.modelValue = v;
                firstChangeSubs.unsubscribe()
            });
        }

        this.model.valueChanges
            .debounceTime(this.debounceTime)
            .distinctUntilChanged()
            .subscribe(mv => {
                if (this.modelValue != mv){
                    this.modelValue = mv;
                    this.onDebounce.emit(mv);
                }
            });
    }
}

用法将是

<textarea [ngModel]="somevalue"   
          [debounce]="2000"
          (onDebounce)="somevalue = $event"                               
          rows="3">
</textarea>

您还可以使用装饰器解决此问题,例如,使用utils-decorator lib(npm install utils-decorators)中的去抖动装饰器解决一个问题

import {debounce} from 'utils-decorators';

class MyAppComponent {

  @debounce(500)
  firstNameChanged($event, first) {
   ...
  }
}

花了几个小时,希望我可以节省一些时间。对我来说,debounce在控件上使用以下方法对我来说更直观,更容易理解。它基于用于自动完成的angular.io docs解决方案而构建,但具有让我能够拦截呼叫的能力,而不必依赖于将数据绑定到DOM。

柱塞

一个用例是在输入用户名后检查用户名是否已经被使用,然后警告用户。

注意:别忘了,(blur)="function(something.value)根据您的需要可能对您来说更有意义。

使用RxJS v6在Angular 7中进行DebounceTime

链接

演示链接

在此处输入图片说明

在HTML模板中

<input type="text" #movieSearchInput class="form-control"
            placeholder="Type any movie name" [(ngModel)]="searchTermModel" />

在组件中

    ....
    ....
    export class AppComponent implements OnInit {

    @ViewChild('movieSearchInput') movieSearchInput: ElementRef;
    apiResponse:any;
    isSearching:boolean;

        constructor(
        private httpClient: HttpClient
        ) {
        this.isSearching = false;
        this.apiResponse = [];
        }

    ngOnInit() {
        fromEvent(this.movieSearchInput.nativeElement, 'keyup').pipe(
        // get value
        map((event: any) => {
            return event.target.value;
        })
        // if character length greater then 2
        ,filter(res => res.length > 2)
        // Time in milliseconds between key events
        ,debounceTime(1000)        
        // If previous query is diffent from current   
        ,distinctUntilChanged()
        // subscription for response
        ).subscribe((text: string) => {
            this.isSearching = true;
            this.searchGetCall(text).subscribe((res)=>{
            console.log('res',res);
            this.isSearching = false;
            this.apiResponse = res;
            },(err)=>{
            this.isSearching = false;
            console.log('error',err);
            });
        });
    }

    searchGetCall(term: string) {
        if (term === '') {
        return of([]);
        }
        return this.httpClient.get('http://www.omdbapi.com/?s=' + term + '&apikey=' + APIKEY,{params: PARAMS.set('search', term)});
    }

    }

这是迄今为止我找到的最好的解决方案。更新ngModelblurdebounce

import { Directive, Input, Output, EventEmitter,ElementRef } from '@angular/core';
import { NgControl, NgModel } from '@angular/forms';
import 'rxjs/add/operator/debounceTime'; 
import 'rxjs/add/operator/distinctUntilChanged';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/fromEvent';
import 'rxjs/add/operator/map';

@Directive({
    selector: '[ngModel][debounce]',
})
export class DebounceDirective {
    @Output()
    public onDebounce = new EventEmitter<any>();

    @Input('debounce')
    public debounceTime: number = 500;

    private isFirstChange: boolean = true;

    constructor(private elementRef: ElementRef, private model: NgModel) {
    }

    ngOnInit() {
        const eventStream = Observable.fromEvent(this.elementRef.nativeElement, 'keyup')
            .map(() => {
                return this.model.value;
            })
            .debounceTime(this.debounceTime);

        this.model.viewToModelUpdate = () => {};

        eventStream.subscribe(input => {
            this.model.viewModel = input;
            this.model.update.emit(input);
        });
    }
}

https://stackoverflow.com/a/47823960/3955513借来的

然后在HTML中:

<input [(ngModel)]="hero.name" 
        [debounce]="3000" 
        (blur)="hero.name = $event.target.value"
        (ngModelChange)="onChange()"
        placeholder="name">

blur模型上使用普通javascript进行了显式更新。

此处的示例:https : //stackblitz.com/edit/ng2-debounce-working

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