无法读取未定义的“xxx"的属性 [英] Cannot read property of 'xxx' of undefined
问题描述
我使用的是 Ionic 2,其中一个组件有两个组件,并且使用发射器共享数据.但是当我执行程序时,就出现了这个错误.
I'm using Ionic 2, in which a component has two components and the data were shared using emitters. But when I execute the program, it comes to this error.
运行时错误未捕获(承诺):类型错误:无法读取属性未定义类型错误的BillNo":无法读取属性BillNo"在 Object.eval [as updateDirectives] 处未定义
Runtime Error Uncaught (in promise): TypeError: Cannot read property 'BillNo' of undefined TypeError: Cannot read property 'BillNo' of undefined at Object.eval [as updateDirectives]
这是我的代码:
bill-settlement.html
...
<page-bill-list (BillSelected)="onBillSelected($event)"></page-bill-list>
...
<page-bill-details [billItem]="billItem"></page-bill-details>
...
bill-settlement.ts
@Component({
selector: 'page-bill-settlement',
templateUrl: 'bill-settlement.html',
})
export class BillSettlement {
...
billItem: BillDetail
...
onBillSelected(billData: BillDetail) {
this.billItem = billData
}
}
bill-list.html
<ion-buttons>
<button ion-button *ngFor="let item of billItems" (click)="getBillDetails(item)">
{{item.BillNo}}
</button>
</ion-buttons>
bill-list.ts
@Component({
selector: 'page-bill-list',
templateUrl: 'bill-list.html',
})
export class BillList {
billItems: BillDetail[] = []
billItem = new BillDetail()
@Output() BillSelected = new EventEmitter<BillDetail>()
constructor(public navCtrl: NavController,
public navParams: NavParams,
public billSrv: BillerService,
public authSrv: AuthService,
public genSrv: GenericService) {
this.billSrv.getBills()
.subscribe(data => {
this.billItems = data
})
}
getBillDetails(item: BillDetail) {
this.BillSelected.emit(this.billItem)
}
}
bill-details.ts
@Component({
selector: 'page-bill-details',
templateUrl: 'bill-details.html',
})
export class BillDetails {
...
@Input() billItem: BillDetail
...
}
bill-details.html
...
<ion-input text-right type="text" [value]="billItem.BillNo" readonly></ion-input> //billItem model has BillNo property
...
问题是bill-details.ts
中的billItem.BillNo
最初没有值,只有当我点击中的账单编号按钮时才定义bill-list.html
.我如何最初定义 billItem,然后在单击账单编号按钮时进行替换.
The problem is billItem.BillNo
in bill-details.ts
has no value initially, it is defined only when I click the bill number button in the bill-list.html
. How can i define the billItem initially and then replaces when clicked with the bill number button.
推荐答案
在设置 billItem
之前加载视图.
The view is loaded before billItem
is set.
您可以使用安全导航操作符?
.
You could use a safe navigation operator ?
.
<ion-input text-right type="text" [value]="billItem?.BillNo" readonly></ion-input> //billItem model has BillNo property
或者在bill-details.ts的构造函数中设置为空对象:
or set it to empty object in the constructor of bill-details.ts:
constructor(...){
if(! this.billItem){
this.billItem={}
}
}
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