Question

我必须通过forEach多次调用服务，该方法内部具有订阅（http调用）的功能，并且每次都必须等待上一次调用的结束。这是代码：

itemDefaultConfiguration.command = (onclick) => {
   this.createConfiguration(configuration.components);
   //wait the end of createConfiguration method that has subscribe (http call) inside
   this.initializeAllComponents(configuration.components)
};

initializeAllComponents(components: Agent[]) {
    components.forEach(agent => {
      this.componentService.setAgent(agent);
      this.componentService.clearAnyOneOfIndex();
      // wait the end of setAgent method that has subscribe(http call) inside
    })
}

内部componentService：

setAgent(agent: Agent) {
        this.agent = agent;
        this.selectComponent(agent.name, undefined, "/", "/", environment.maxLevelJsonSchema);
    }

和selectComponent具有订阅。

selectComponent(agentName: string, propName: string, schemaPath: string, dataPath: string, deepLevel: number) {
        this.getComponentSchema(this.agentName, schemaPath, deepLevel)
            .subscribe((responseSchema) => {
                this.getDataFailure(propName, dataPath, responseSchema); 
            });
}

你能帮我吗？谢谢

Answer 1

您可以使用await来做到这一点，例如：

initializeAllComponents(components: Agent[]) {
    components.forEach(async agent => {
      await this.componentService.setAgent(agent).catch(console.log);
      this.componentService.clearAnyOneOfIndex();
      // wait the end of setAgent method that has subscribe(http call) inside
    })
}

Answer 2

您可以使用async/await语法来实现：

initializeAllComponents(components: Agent[]) {
    for (let i = 0; i < components.length; i++) {
        const agent = components[i];
        await this.componentService.setAgent(agent).catch(console.log);
        this.componentService.clearAnyOneOfIndex();
    }
}

请注意async/await，因为您需要使用本机for循环才能等待上一个调用-forEach，reduce和类似方法只会触发多个异步电话。

Answer 3

如果是param_b，请尝试使用Observable运算符：

switchMap

如果不是import { switchMap } from 'rxjs/operators'; import { of } from 'rxjs/observable/of'; initializeAllComponents(components: Agent[]) { components.forEach(agent => { this.componentService.setAgent(agent).pipe( switchMap(res => { if (res) { return this.userService.get(user.uid); } return of(null); })); ); this.componentService.clearAnyOneOfIndex(); }) }，则使用Observable运算符：

async/await

带有订阅内部的Angular 6等待方法

3 个答案: