Question

我想运行这段简单的代码，基本上它会根据状态（字符串）更改标签和图标

  <ng-container *ngIf="container.length > 0">
                <span *ngIf="!container.status.includes('Paused') && container.status.includes('Up')"
                      class="label label-success label-lg-status"><span class="fa fa-check"></span> Completed - {{ container.status }}</span>
                <span *ngIf="container.status.includes('Paused')" class="label label-warning label-lg-status"><span
                  class="fa fa-pause"></span> Completed - {{ container.status }}</span>
                <span *ngIf="container.status.includes('Exited')" class="label label-danger label-lg-status"><span
                  class="fa fa-stop"></span> Completed - {{ container.status }}</span>
   </ng-container>

但是我收到一个错误，说不能使用包含null，所以我放*ngIf="container.length > 0"现在我得到ReportComponent.html:22 ERROR TypeError: Cannot read property 'length' of null

如何让html等待执行get请求？

export class ReportComponent implements OnInit {

  private containerName:string;
  private processes = [];
  private container = [];
  private settings = [];
  private environment = [];
  private id:Number;

  constructor(private _route:ActivatedRoute, private dockerService:DockerService, private environmentService:EnvironmentService, private settingsService:SettingsService) { }

  ngOnInit() {
      // Get Environment id
      this._route.params.subscribe(params => {
        this.id = params['id'];
        // Get Environment
        this.environmentService.getEnvironment(this.id).subscribe( environment => {
          this.environment = environment;
          console.log(environment);
          //this.containerName = this.environment.name;
        });
        // Get Docker processes
        this.dockerService.getProcesses(this.containerName).subscribe(processes => {
          this.processes = processes;
        });
        // Get Docker Container Object
        this.dockerService.getContainer(this.containerName).subscribe( container => {
          this.container = container;
        });
        // Get Settings
        this.settingsService.getSettings().subscribe( settings => {
          this.settings = settings;
        });
    });
  }
}

Answer 1

使用它像：

*ngIf="container && (container.length > 0)"

错误将被删除。

除非length数组可用，否则不会检查container。

Answer 2

是的可以像这样使用它，它会更加Angular方式

  <ng-container *ngIf="container?.length > 0">

它也会起作用。

Answer 3

您确切的问题是服务调用是异步的。因此，DOM绑定在container对象中绑定值之前启动。因为DOM呈现不等待异步服务响应的完成

解决方法是，你应该在nginit中初始化你的数组。

试试这个

 ngOnInit() {
       this.container = []//add this
      // Get Environment id
      this._route.params.subscribe(params => {
        this.id = params['id'];
        // Get Environment
        this.environmentService.getEnvironment(this.id).subscribe( environment => {
          this.environment = environment;
          console.log(environment);
          //this.containerName = this.environment.name;
        });
        // Get Docker processes
        this.dockerService.getProcesses(this.containerName).subscribe(processes => {
          this.processes = processes;
        });
        // Get Docker Container Object
        this.dockerService.getContainer(this.containerName).subscribe( container => {
          this.container = container;
        });
        // Get Settings
        this.settingsService.getSettings().subscribe( settings => {
          this.settings = settings;
        });
    });
  }
}

类型错误：无法读取属性＆＃39;长度＆＃39;为null

3 个答案: