无法读取未定义 Angular 6 的属性“nativeElement”

Question

我正在尝试为我的应用创建自定义 Spinner 组件，所以我已经创建了

spinner.component.ts

export class SpinnerComponent implements AfterViewInit {

    @ViewChild("spinner") spinner: ElementRef;

    constructor() { }

    ngAfterViewInit(): void {
        this.spinner.nativeElement.style.display = "none";
    }

    public show = (): void => { this.spinner.nativeElement.style.display = "block"; };

    public hide = (): void => { this.spinner.nativeElement.style.display = "none"; };

}

spinner.component.ts

<img #spinner src="assets/images/dotSpinner.gif" class="loading"/>

我正试图在我的其他组件中控制这个微调器，比如

sample.component.ts

import { SpinnerComponent } from "../spinner/spinner.component";

export class SimpleComponent {

    private spinner: SpinnerComponent = new SpinnerComponent();

    constructor() {}

    actionHandler = (data: any): void => {
        this.spinner.show();
        this.clientActionService.subscribe(
            data => {
                this.spinner.hide();
                this.clientAction = data;
            },
            err => {
                this.spinner.hide();
            }
        );
    }

}

但我遇到了错误 错误类型错误：无法读取未定义的属性“nativeElement” 在 SpinnerComponent.show

Answer 1

如果你想要解决方法，那么

<img
    [ngStyle]="{'display': displayVal}"
    src="assets/images/dotSpinner.gif"
    class="loading"/>

打字稿代码

display = "none";
public show = (): void => { this.displayVal = "block"; };
public hide = (): void => { this.displayVal = "none"; };

Answer 2

使用 forwardRef

forwardRef 用于当我们需要引用的令牌时 DI 的用途已声明，但尚未定义。它也用于 我们在创建查询时使用的令牌尚未定义。

   import { SpinnerComponent } from "../spinner/spinner.component";   
    export class SimpleComponent {   
        constructor(constructor(@Inject(forwardRef(() => SpinnerComponent )) private ref:any)) {}

        actionHandler = (data: any): void => {
            this.ref.show();
            this.clientActionService.subscribe(
                data => {
                    this.ref.hide();
                    this.clientAction = data;
                },
                err => {
                    this.ref.hide();
                }
            );
        }

    }

Answer 3

spinner.component.ts // html 代码

 <img *ngIf="isShowSpinner" src="assets/images/dotSpinner.gif" class="loading"/>

 <button (click)="show()"> Show </button>
 <button (click)="hide()"> Hide </button>

spinner.component.ts //打字稿代码

public isShowSpinner: boolean = false;
constructor() { }

public show() { this.isShowSpinner = true; }    
public hide() { this.isShowSpinner = false; }

请试试这个。