我在处理角度的promise函数时缺乏对异步操作的理解。所以基本上,我试图从promise方法中获取一个值并将其分配给组件中的全局变量。但是,当我单击一次按钮时,我无法检索该值,并且在我再次单击按钮后它最终开始显示该值。
我点击一次:
时出错 Cannot read property 'matchId' of undefined
我点击两次后获得的价值:
3
HTML:
<button type="submit" (click)="loadInfo(form)">Submit</button>
服务:
@Injectable()
export class Web3Service {
constructor...
getInfo(address: string): Promise<any> {
return this.TestBetting.deployed().then((instance) => {
return instance.getInfo.call(address);
})
.then((value) => {
var serialized = this.itemsService.getSerialized<IGetInfo>(value);
return this.mappingService.mapValueToGetInfo(serialized);
})
.catch((e) => {
console.log(e);
});
}
}
组件:
export class HomeComponent {
infoMapped: any;
constructor(private web3Service: Web3Service) {}
loadInfo(): void {
var test = this.web3Service.getInfo(this.address);
test.then((value) => {
this.infoMapped = value;
})
// this.infoMapped.matchId is undefined on a first attempt
var length = this.infoMapped.matchId;
for (var i = 0; i < length; i++) {
//...
}
}
}
需要修复哪些内容才能在仅按一次按钮后检索infoMapped
值?
答案 0 :(得分:1)
问题仍然是代码 test.then()
(即for
)将在<{strong> this.infoMapped = value;
之前执行因为{ {1}}仅在this.infoMapped = value;
承诺解决时执行,并且只会在 test
运行后解析一段时间。
我建议:移动&#34;处理&#34;新方法的逻辑,并从for
。
所以,这个:
.then()
会变成这样:
loadInfo(): void {
var test = this.web3Service.getInfo(this.address);
test.then((value) => {
this.infoMapped = value;
})
// this.infoMapped.matchId is undefined on a first attempt
var length = this.infoMapped.matchId;
for (var i = 0; i < length; i++) {
//...
}
}