Question

我正在使用Angular 5.2.9。

我想知道何时应该使用Renderer2而不是ngStyle？哪个是最好的解决方案？

1：<div #div>FOO BAR</div>

  @ViewChild('div') div: ElementRef;

  constructor(private renderer: Renderer2) {}

  ngAfterViewInit() {
      this.renderer.setStyle(this.div.nativeElement, 'background', 'blue');
  }

2：<div [ngStyle]="styleValue">FOO BAR</div>

  styleValue: any = {};

  ngAfterViewInit() {
      this.styleValue = {background: 'blue'};
  }

我知道它更容易使用＆＃34; ngStyle＆＃34;在ngFor中，例如：

<div ngFor="let elem of array" [ngStyle]="styleValue">

否则你应该为这种情况做：<div ngFor="let elem of array" #div>FOO BAR</div>

  @ViewChildren('div') divs: QueryList<ElementRef>;

  constructor(private renderer: Renderer2) {}

  ngAfterViewInit() {
     this.divs.change.subscribe(() => {
        this.toFlipArray.forEach((div) => {
            this.renderer.setStyle(this.div.nativeElement, 'background', 'blue');
        })
     }
  }

这在使用Renderer2的ngFor中似乎要长得多，我甚至没有杀死订阅。

性能有差异吗？也许在其他地方？

Answer 1

ngStyle和renderer.setStyle都用于动态设置组件样式

但renderer.setStyle看起来优先于[ngStyle]，即使ngStyle看起来是一种嵌入式广告。

演示示例：

https://stackblitz.com/edit/angular-jtdk4z?file=src%2Fapp%2Fapp.component.html

在查看ngStyle的内部实现时：

https://github.com/angular/angular/blob/master/packages/common/src/directives/ng_style.ts

看起来它本身是使用renderer.setStyle
实现的

@Directive({selector: '[ngStyle]'})
export class NgStyle implements DoCheck {
  private _ngStyle: {[key: string]: string};
  private _differ: KeyValueDiffer<string, string|number>;

  constructor(
      private _differs: KeyValueDiffers, private _ngEl: ElementRef, private _renderer: Renderer2) {}

  @Input()
  set ngStyle(v: {[key: string]: string}) {
    this._ngStyle = v;
    if (!this._differ && v) {
      this._differ = this._differs.find(v).create();
    }
  }

  ngDoCheck() {
    if (this._differ) {
      const changes = this._differ.diff(this._ngStyle);
      if (changes) {
        this._applyChanges(changes);
      }
    }
  }

  private _applyChanges(changes: KeyValueChanges<string, string|number>): void {
    changes.forEachRemovedItem((record) => this._setStyle(record.key, null));
    changes.forEachAddedItem((record) => this._setStyle(record.key, record.currentValue));
    changes.forEachChangedItem((record) => this._setStyle(record.key, record.currentValue));
  }

  private _setStyle(nameAndUnit: string, value: string|number|null|undefined): void {
    const [name, unit] = nameAndUnit.split('.');
    value = value != null && unit ? `${value}${unit}` : value;

    if (value != null) {
      this._renderer.setStyle(this._ngEl.nativeElement, name, value as string);
    } else {
      this._renderer.removeStyle(this._ngEl.nativeElement, name);
    }
}

ngStyle VS Renderer2？我该怎么用？

1 个答案: