angular - ngStyle VS 渲染器2？我应该使用什么？

Question

我正在使用 Angular 5.2.9。

我想知道什么时候应该使用 Renderer2 而不是 ngStyle ？哪个是最佳解决方案？

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'};
  }

我知道在 ngFor 中使用“ngStyle”更容易，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');
        })
     }
  }

在 ngFor 中使用 Renderer2 似乎要长得多，我什至没有终止订阅。

性能有区别吗？也许在其他地方？

Answer 1

两者都是 ngStyle和 renderer.setStyle用于动态设置组件样式

但是renderer.setStyle看起来优先于 [ngStyle]即使ngStyle看起来是一种嵌入式风格。

演示示例:

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

When looking to the internal implementation of ngStyle:

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

it looks like it itself is implemented using renderer.setStyle

@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);
    }
}