angular2中的可投影节点是什么

Question

在阅读ViewContainerRef和ComponentFactory的文档时,例如我们有方法

ViewContainerRef#createComponent包含3个参数:componentFactory,injector和projectableNodes.

我已经尝试查找projectableNodes它们在博客,教程和源代码中使用的含义和方式,但找不到多少.

在查找用于ngComponentOutlet指令的diff时,我可以收集的是,projectableNodes中的字符串被"投影"或呈现在创建的组件视图上(如ng-content可能).如果是这样会让人感到困惑,因为我们有相同的ViewContainerRef#createEmbeddedView.

我想知道这些是什么,projectedNodes并举例说明它们的用法.

Answer 1

可投影节点是节点元素(即实现节点接口的元素),它们被"投影"或换句话说,被转换到ng-content我们在组件模板中的节点元素.

例如,我们可以通过以下方式创建节点元素:

var myNode = document.createElement('div');
var text = document.createTextNode('this is my text');
myNode.appendChild(text);

然后我们可以使用上面的节点,方法如下:

constructor(private vcr:ViewContainerRef ) {

}
ngAfterViewInit() {

  let cmpFactory = this.vcr.resolveComponentFactory(MyDynamicComponent);
  let injector = this.vcr.parentInjector;

  var myNode = document.createElement('div');
  var text = document.createTextNode('this is my text');
  myNode.appendChild(text);
  this.vcr.createComponent(cmpFactory,0,injector,[ [ myNode ] ])
}

投影节点接受二维数组,因为我们可以进行多时隙转换,即不止一个ng-content.

以下是如何使用可投影节点的完整示例ViewContainerRef#createComponent.此示例动态创建一个包含transclsion/ng-content的组件:

import { Component, ViewContainerRef, ComponentFactoryResolver } from '@angular/core';
import { ComponentFactory,ComponentRef, Renderer } from '@angular/core';

@Component({
    selector: 'sample',
    template: '<ng-content></ng-content><ng-content></ng-content>'
})
export class Sample { }

@Component({
    selector: 'demo',
    template: '<p>Demo</p>',
    entryComponents: [Sample]
})
export class DemoComponent {

    constructor(private vcr: ViewContainerRef, private cfr: ComponentFactoryResolver, private r: Renderer) { }

    ngAfterViewInit() {
        let cmpFactory = this.cfr.resolveComponentFactory(Sample);
        let injector = this.vcr.parentInjector;
        let demoCompEl = this.vcr.element.nativeElement;

        let projectedElA = this.r.createElement(demoCompEl,'p');
        this.r.createText(projectedElA,'projectable content A');
        this.r.detachView([projectedElA]);

        let projectedElB = this.r.createElement(demoCompEl,'p');
        this.r.createText(projectedElB,'projectable content B');
        this.r.detachView([projectedElB]);

        let projectedC = document.createElement('div');
        let text = document.createTextNode('projectable content C');
        projectedC.appendChild(text);

        let cmpRef = this.vcr.createComponent(cmpFactory,0,injector,[[projectedElA],[projectedElB,projectedC]]);

    }


}

输出:

Demo

projectable content A

projectable content B

projectable content C

需要注意的另一件事是,在我们为可投影节点传递的2d数组中,每个1d数组条目具有属于一起的特定视图的根元素/将在单个ng-content块中一起渲染