Javascript 如何调用使角度服务同步?
我正在尝试从Javascript 如何调用使角度服务同步?,javascript,angular,typescript,angular5,Javascript,Angular,Typescript,Angular5,我正在尝试从localStorage读取项(menulist)。若为null,则调用一个服务,该服务将在从数据库获取菜单列表后存储它)。 服务似乎是异步的,因为在下面的代码中,我无法读取null的属性'sort' ngOnInit() { this.menulist = localStorage.getItem('menulist'); if (!this.menulist) { this.SetMenuList(); } this.jsonmenu
localStorage
读取项(menulist)。若为null,则调用一个服务,该服务将在从数据库获取菜单列表后存储它)。
服务似乎是异步的,因为在下面的代码中,我无法读取null的属性'sort'
ngOnInit() {
this.menulist = localStorage.getItem('menulist');
if (!this.menulist) {
this.SetMenuList();
}
this.jsonmenulist = JSON.parse(this.menulist);
this.jsonmenulist.sort(function (a, b) {
return a.mnuposno > b.mnuposno;
});
this.jsonmenulist = this.jsonmenulist.sort();
}
SetMenuList() {
this._UserspecificmenuaccessService.getRMA("driver")
.subscribe((lst) => {
if (lst && lst.length > 0) {
localStorage.setItem('menulist', JSON.stringify(lst));
this.menulist = localStorage.getItem('menulist');
console.log(this.menulist); // gets called after this.jsonmenulist.sort?
return true;
}
}, (error) => {
console.error(error)
});
}
控制台:
ERROR TypeError: Cannot read property 'sort' of null
[{"mnurecid":"4","mnuid":"menu1","mnuname":"Bin","mnuurl":"/bin/","mnuposno":"1.0","checked":true}, {"mnurecid":"12","mnuid":"menu9","mnuname":"Menu9","mnuurl":"/menu9","mnuposno":"9.0","checked":false}]
您可以编写需要在subscribe函数内执行的代码,以便仅在异步操作完成后执行。您可以编写需要在subscribe函数内执行的代码,以便仅在异步操作完成后执行。您可以使用toPromise()rxjs库中的方法返回承诺,而不是可观察的 所以在您的服务中
getRMA(type) {
return this.http.post(environment.baseURL + '/getmenulist', { drive:
type }, this.options).map((response) => response.json()
).toPromise().catch(e => {
console.log(e);
)}
}
在您的组件中使用异步和等待
async SetMenuList() {
let response = await
this._UserspecificmenuaccessService.getRMA("driver")
console.log(response)
}
您可以使用rxjs库中的toPromise()方法来返回承诺,而不是可观察的 所以在您的服务中
getRMA(type) {
return this.http.post(environment.baseURL + '/getmenulist', { drive:
type }, this.options).map((response) => response.json()
).toPromise().catch(e => {
console.log(e);
)}
}
在您的组件中使用异步和等待
async SetMenuList() {
let response = await
this._UserspecificmenuaccessService.getRMA("driver")
console.log(response)
}
不完全是关于asyncbroblem,您只需在分配它之前使用
this.menulist
。只要改变你运行代码的方式
ngOnInit() {
this.menulist = localStorage.getItem('menulist');
if (this.menulist) {
this.sortMenuList(); // Sorting the menu if we have menulist already
} else {
this.SetMenuList(); // Else call the service and sort the menu then
}
}
sortMenuList() {
this.jsonmenulist = JSON.parse(this.menulist);
this.jsonmenulist.sort(function (a, b) {
return a.mnuposno > b.mnuposno;
});
this.jsonmenulist = this.jsonmenulist.sort();
}
SetMenuList() {
this._UserspecificmenuaccessService.getRMA("driver")
.subscribe((lst) => {
if (lst && lst.length > 0) {
localStorage.setItem('menulist', JSON.stringify(lst));
this.menulist = localStorage.getItem('menulist');
this.sortMenuList(); // Sorting the menu if we have menulist already
}
}, (error) => {
console.error(error)
});
}
顺便说一句,
SetMenuList
命名应该是SetMenuList
(只是建议命名)。不完全是关于asyncbroblem,您只需在分配它之前使用this.menulist
。只要改变你运行代码的方式
ngOnInit() {
this.menulist = localStorage.getItem('menulist');
if (this.menulist) {
this.sortMenuList(); // Sorting the menu if we have menulist already
} else {
this.SetMenuList(); // Else call the service and sort the menu then
}
}
sortMenuList() {
this.jsonmenulist = JSON.parse(this.menulist);
this.jsonmenulist.sort(function (a, b) {
return a.mnuposno > b.mnuposno;
});
this.jsonmenulist = this.jsonmenulist.sort();
}
SetMenuList() {
this._UserspecificmenuaccessService.getRMA("driver")
.subscribe((lst) => {
if (lst && lst.length > 0) {
localStorage.setItem('menulist', JSON.stringify(lst));
this.menulist = localStorage.getItem('menulist');
this.sortMenuList(); // Sorting the menu if we have menulist already
}
}, (error) => {
console.error(error)
});
}
顺便说一下,
SetMenuList
命名应该是SetMenuList
(只是建议命名)。您不能。和的可能副本。改进这一点的一个简单方法是从可观察到的转换为承诺,并在ngOnInit中使用async/await。你不能。和的可能副本。改进这一点的一个简单方法是,从可观察切换到承诺,并在ngOnInit中使用async/await。但我想知道我的选择,我可以。但我想知道我的选择。