ngFor内部的自定义结构指令,在ngFor之前进行更新 [英] Custom structural directive inside ngFor updates before ngFor
问题描述
我正在创建一个小型应用程序,该应用程序使用ngFor显示具有名称,姓氏和年龄字段的人的列表.该应用程序具有搜索字段,可以在其中输入查询,然后根据该查询,服务器将列表替换为新的实体.
I am creating a small application, which display a list of People with Name, Surname and Age fields using ngFor. The application has search field, where one can enter a query, and then the list will get replaced with new Entities from the server, based on that query.
我创建了一条指令,该指令突出显示ngFor行内查询的字母.
I created a directive, that highlights letters from the query inside the ngFor row.
例如,如果我在数据库中有一个人的名字是David,并且在查询中输入"Dav",则只有ngFor的实体会被从服务器中加载,而带有"Dav"的实体将被从服务器中加载,而"Dav"字母将被从服务器中加载.突出显示,而"id"则不会.如果我有David和Davin,两个实体都将突出显示.
For example, if I have a person in database that its name is David, and I enter "Dav" inside my query, only entities conatining "Dav" will be loaded from the server in ngFor, and "Dav" letters will be highlighted and "id" will be not. If I have David and Davin, both entities will be highlighted.
仅当我使用人工setTimeout()时,该指令才能按预期工作,以确保在该指令执行操作之前将加载新列表.还有其他方法可以使这项工作吗?
The directive works as expected only if I am using an artifical setTimeout(), to make sure that the new list will load before the Directive takes action. Is there any other way to make this work?
指令:
import { Directive, Input, ElementRef } from '@angular/core';
import { SimpleChanges, Renderer2 } from '@angular/core';
@Directive({
selector: '[appQueryHighlight]'
})
export class QueryHighlightDirective {
@Input('appQueryHighlight') query: string;
queryPos: number;
paragraphElement: HTMLParagraphElement;
constructor(private element: ElementRef, private renderer: Renderer2) {
this.paragraphElement = (<HTMLParagraphElement>this.element.nativeElement);
}
ngOnChanges(changes: SimpleChanges){
// Temporary timeout solution
setTimeout(()=>{
var childCount = this.paragraphElement.childElementCount;
var text: string = "";
// If paragraph contain SPANS, we need to flat them to innerHTML
if(childCount > 1) {
for(var i = 0; i < childCount; i++) {
text += (<HTMLSpanElement>this.paragraphElement.childNodes[0]).innerHTML;
console.log("SPAN" + (<HTMLSpanElement>this.paragraphElement.childNodes[0]).innerHTML);
this.paragraphElement.removeChild(this.paragraphElement.childNodes[0]);
}
console.log("Text=" + text)
this.paragraphElement.innerHTML = text;
}
console.log('Directive ngOnChanges: query=' + this.query + ", paragraph=" + this.paragraphElement.innerHTML);
this.queryPos = this.paragraphElement.innerHTML.toUpperCase().indexOf(this.query.toUpperCase());
if(this.query!="" && this.queryPos >= 0) {
//this.paragraphElement.style.backgroundColor = 'yellow';
//First span, containing pre-colored text
var span1 = this.renderer.createElement('span');
var text1 = this.renderer.createText(this.paragraphElement.innerHTML.substring(0,this.queryPos));
this.renderer.appendChild(span1, text1);
//Colored text span, containing query
var span2 = this.renderer.createElement('span');
var text2 = this.renderer.createText(this.paragraphElement.innerHTML.substr(this.queryPos, this.query.length));
this.renderer.setStyle(span2, 'color', "red");
this.renderer.setStyle(span2, 'text-decoration', "underline");
this.renderer.appendChild(span2, text2);
//Third span, containing text after query
var span3 = this.renderer.createElement('span');
var text3 = this.renderer.createText(this.paragraphElement.innerHTML.substring(this.queryPos + this.query.length));
this.renderer.appendChild(span3, text3);
this.paragraphElement.innerHTML = "";
this.renderer.appendChild(this.paragraphElement, span1);
this.renderer.appendChild(this.paragraphElement, span2);
this.renderer.appendChild(this.paragraphElement, span3);
}
else {
//this.paragraphElement.style.color = 'black';
}
}, 15);
}
}
LIST-COMPONENT.TS:
LIST-COMPONENT.TS:
ngOnChanges(changes: SimpleChanges) {
this.debtsService.getFilteredDebts(this.query)
.subscribe(
(data) => {
this.debtsList = data;
this.afterFilteringQuery = this.query;
},
(err) => console.log("Error occured: " + err)
);
}
LIST-COMPONENT.HTML:
LIST-COMPONENT.HTML:
<app-person-item
*ngFor="let person of personList;"
[query]="afterFilteringQuery">
</app-person-item>
推荐答案
您可以尝试使用BehaviorSubject
方法来代替ngOnChanges
方法.我不确定,但是Observable的.next()
调用应保证有一个额外的事件循环周期,这对于您的情况是必需的,因为我们可以看到每个有效的setTimeout
调用为零.
Instead of ngOnChanges
approach you may try to apply BehaviorSubject
approach . I'm not sure but Observable's .next()
call should guarantee an additional event loop cycle which is necessary in your case as we can see per working zero setTimeout
call.
import { Directive, Input, ElementRef, Renderer2 } from '@angular/core';
import { BehaviorSubject } from 'rxjs/BehaviorSubject';
@Directive({
selector: '[appQueryHighlight]'
})
export class QueryHighlightDirective {
private _query = new BehaviorSubject<string>('');
@Input('appQueryHighlight')
set query(value: string) {
this._query.next(value);
};
get query(): string {
return this._query.getValue();
}
ngOnInit() {
this._query.subscribe((query: string) => {
// on query change handler
// ... ngOnChanges-setTimeout previous code with 'query' instead of 'this.query'
});
}
}
这篇关于ngFor内部的自定义结构指令,在ngFor之前进行更新的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!