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Angular 2 ContentChild 应用 Html 属性
[英] Angular 2 ContentChild Apply Html Attributes
本文介绍了Angular 2 ContentChild 应用 Html 属性的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我有一个自定义组件，可将引导程序表单组应用于我的表单字段.在我的组件中，我有以下属性:
import { Component, Input, ContentChild } from '@angular/core';从 '@angular/common' 导入 { NgControl };@成分({选择器:'表单域'，模板:`<div class="form-group" [ngClass]="{'has-error':(state && !state.valid && state.touched)}"><label *ngIf="label" [attr.for]="state.name" class="col-sm-3 control-label">{{label}}</label><div class="col-sm-9"><ng-content></ng-content><div *ngIf="state && !state.valid && state.errors && state.touched" class="help-block text-danger"><span *ngIf="state.errors.required">{{label?label:'This field'}} 是必需的</span><span *ngIf="state.errors.min">{{label?label:'Value'}} 太小</span>
`})导出类 FormFieldComponent{@输入()标签:字符串；@ContentChild(NgControl) 状态；}
在我的模板中，我像这样使用我的组件:
我想知道有没有办法通过我的组件动态设置控件的占位符文本?
我希望将标签设置为输入字段的占位符，即
解决方案
该指令适用于所有具有 ngControl 或 [ngControl]="..." 属性的输入元素.它在应用它的元素上设置 placeholder 属性.
使用
使其在全球范围内可用bootstrap(App, [提供(PLATFORM_DIRECTIVES，{useValue:[InputLabel]，multi:true})])
@Directive({选择器:['[ngControl]']})导出类 InputLabel {@输入()@HostBinding('attr.placeholder')标签;构造函数(){console.log('InputLabel');}}
在 FormField 组件中，查询该指令并将来自输入的标签传递给指令(在 ngOnChanges 或 ngAfterContentChecked 中) -基本上是 label 和 state 可用的第一次出现.
@Component({选择器:'表单域'，提供者:[]，模板:`<div><ng-content></ng-content>
`，指令:[]})导出类 FormField {@Input() 标签:字符串；@ContentChild(InputLabel) 状态；ngOnChanges() {if(this.label && this.state) {this.state.label = this.label;}}ngAfterContentInit() {if(this.label && this.state) {this.state.label = this.label;}}}
这只是为了演示它是如何使用的:
@Component({选择器:'我的应用'，提供者:[]，模板:`<div><h2>你好{{name}}</h2><表格><form-field label="名字"><input ngControl="firstName" type="text"></表单域></表单>
`，指令:[FormField，FORM_DIRECTIVES]})出口类应用{构造函数(FB:FormBuilder){this.name = 'Angular2(发布候选！)'this.form = fb.group({firstName: [""]});}}
Plunker 示例
我选择这种方法是因为我无法通过其他东西(NgControl，...)进行查询并获得对输入元素的引用.
没有必要以这种方式提供指令.它也可以像任何其他自定义指令一样提供，方法是将其添加到 directives: [InputLabel] 上使用它的 @Component() 装饰器.
I have a custom component that applies bootstrap form group to my form fields. In my component I have below properties:
import { Component, Input, ContentChild } from '@angular/core';
import { NgControl } from '@angular/common';
@Component({
selector: 'form-field',
template: `
<div class="form-group" [ngClass]="{'has-error':(state && !state.valid && state.touched)}">
<label *ngIf="label" [attr.for]="state.name" class="col-sm-3 control-label">{{label}}</label>
<div class="col-sm-9">
<ng-content></ng-content>
<div *ngIf="state && !state.valid && state.errors && state.touched" class="help-block text-danger">
<span *ngIf="state.errors.required">{{label? label:'This field'}} is required</span>
<span *ngIf="state.errors.min">{{label? label:'Value'}} too small</span>
</div>
</div>
</div>
`
})
export class FormFieldComponent{
@Input()
label: string;
@ContentChild(NgControl) state;
}
And in my template I use my component like this:
<form [ngFormModel]="form" (ngSubmit)="onSubmit()" novalidate>
<form-field label="First Name">
<input ngControl="firstName" type="text">
</form-field>
</form>
I was wondering is there any way to dynamically set the placeholder text for the control through my component?
I want the label to be set as placeholder of the input field i.e.
解决方案
This directive is applied to all input elements that have a ngControl or [ngControl]="..." attribute. It sets the placeholder attribute on the element where it is applied.
It is made globally available using
bootstrap(App, [
provide(PLATFORM_DIRECTIVES, {useValue: [InputLabel], multi: true})
])
@Directive({
selector: ['[ngControl]']
})
export class InputLabel {
@Input()
@HostBinding('attr.placeholder')
label;
constructor() {
console.log('InputLabel');
}
}
In the FormField component this directive is queried for and the label from the input is passed to the directive (in ngOnChanges or ngAfterContentChecked - basically the first occurence where label and state are available.
@Component({
selector: 'form-field',
providers: [],
template: `
<div>
<ng-content></ng-content>
</div>
`,
directives: []
})
export class FormField {
@Input() label: string;
@ContentChild(InputLabel) state;
ngOnChanges() {
if(this.label && this.state) {
this.state.label = this.label;
}
}
ngAfterContentInit() {
if(this.label && this.state) {
this.state.label = this.label;
}
}
}
This is just to demonstrate how its used:
@Component({
selector: 'my-app',
providers: [],
template: `
<div>
<h2>Hello {{name}}</h2>
<form>
<form-field label="First Name">
<input ngControl="firstName" type="text">
</form-field>
</form>
</div>
`,
directives: [FormField, FORM_DIRECTIVES]
})
export class App {
constructor(fb:FormBuilder) {
this.name = 'Angular2 (Release Candidate!)'
this.form = fb.group({firstName: [""]});
}
}
Plunker example
I choose this approach because I wasn't able to query by something else (NgControl, ...) and get a reference to the input element.
It's not necessary to provide the directive this way. It can also be provided like any other custom directive by adding it to directives: [InputLabel] on the @Component() decorator where it is used.
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