我大部分时间都有工作的Angular反应形式。但是有时候,我随机得到一个错误
ERROR Error: Cannot find control with name: 'username'
at _throwError (forms.js:2337)
at setUpControl (forms.js:2245)
at FormGroupDirective.push../node_modules/@angular/forms/fesm5/forms.js.FormGroupDirective.addControl (forms.js:5471)
at FormControlName.push../node_modules/@angular/forms/fesm5/forms.js.FormControlName._setUpControl (forms.js:6072)
at FormControlName.push../node_modules/@angular/forms/fesm5/forms.js.FormControlName.ngOnChanges (forms.js:5993)
at checkAndUpdateDirectiveInline (core.js:21093)
at checkAndUpdateNodeInline (core.js:29495)
at checkAndUpdateNode (core.js:29457)
at debugCheckAndUpdateNode (core.js:30091)
at debugCheckDirectivesFn (core.js:30051)
该组件是一个简单的登录页面,HTML是
<div id="loginSection" class="middle-dashboard-box">
<div class="login-title content-inner-title" i18n="logintitle|@@loginheader">Login</div>
<form class="login-form" [formGroup]="loginFormGroup" (ngSubmit)="login($event)">
<mymat-form-error></mymat-form-error>
<div>
<mat-form-field class="login-input input-control-width">
<input matInput formControlName="username" i18n-placeholder="Username|@@username" placeholder="Username">
</mat-form-field>
</div>
<div>
<mat-form-field class="login-input input-control-width">
<input matInput formControlName="password" type="password" i18n-placeholder="Password|@@password" placeholder="Password">
</mat-form-field>
</div>
<div class="forgot-pass">
<a href="#public/forgotpassword" i18n="forgot password|@@forgotPasswordLink">Forgot password?</a>
</div>
<button mat-raised-button color="primary" type="submit" class="main-btn login-btn"
i18n="Login|Login button action@@login">Login</button>
</form>
</div>
TS是
@Component( {
templateUrl: './login.component.html',
styleUrls: ['./login.component.scss']
} )
export class LoginComponent implements OnInit {
loginFormGroup: FormGroup;
constructor( private router: Router,
private formBuilder: FormBuilder,
private loginService: LoginService ) { }
ngOnInit() {
this.loginFormGroup = this.formBuilder.group( {
username: ['', Validators.required],
password: ['', Validators.required]
} );
this.loginFormGroup.controls['username'].setValue( this.loginService.latestUsername );
}
login( event ) {
// do login stuff, not relevant here
}
}
this.loginService.latestUsername
指向LoginService中的获取器:get latestUsername(): string {
return localStorage.getItem( LoginService.LATESTUSERNAME_KEY ) || ''
}
stacktrace中的
FormControlName.ngOnChanges
使我认为ng在控件正确初始化之前正在运行更改检测,但是由于周围没有订阅或类似内容,因此我看不到是什么触发了它。我正在Selenium测试期间观察到错误(某些测试可靠地进行,而其他测试则间歇地进行),但是在手动单击时出现了一次或两次。该效果仅在升级到Angular 8.2.14(从7开始)之后发生
最佳答案
查看FormControlName
的source code并考虑when ngOnChanges() can run,我认为ngOnChanges()
在ngOnInit()
完成构建表单之前正在运行。
为了诊断这一点,我将ngOnChanges()
和ngOnInit()
都用console.log()
乱码,以跟踪发生的情况。
要解决此问题(如果是原因所在),它应该与使用*ngIf
保护表单一样简单,以确保指令不会过早触发更改检测。理想情况下,您还可以使用OnPush
更改检测策略。