Creating a dynamic repeater with ng-content transc

问题:

What I'm trying to achieve is a generic component that is bound to an array of arbitrary objects that allows adding and removing rows dynamically when the view of each row is also arbitrarily defined with components by a master component that uses it.

Note that MasterComponent is an arbitrary component that would be implemented for different pages and is intended to be self contained and not defined by any metadata or external source.

What I have so far are the following Components:

RepeaterComponent template:

<input type="button" value="Add" (click)="addRow()">
<div class="repeater" *ngFor="let row of repeaterArray">
    <div class="repeaterRow">
        <input type="button" value="Remove" (click)="removeRow(row.rowId)">
        <ng-content select="row"></ng-content>
     </div>
</div>

MasterComponent template:

<repeater [repeaterArray]="repeaterObj">
    <row>
        <field-textbox [data]="row.name" [label]="'Name'"></field-textbox>
        <field-textbox [data]="row.description" [label]="'Description'"></field-textbox>
    </row>
</repeater>

The <field-textbox> component is a custom component that I use to encapsulate simple inputs that holds some additional data that I need to use.

The MasterComponent holds an object that for this instance looks like this:

repeaterObj = [
{
    "rowId": 1,
    "name": "First brand",
    "description": "First description"
},
{
    "rowId": 2,
    "name": "Second brand",
    "description": "Second description"
},
{
    "rowId": 3,
    "name": "Third brand",
    "description": "Third description"
}
];

This approach has two issues that I can't seem to find a solution for.

1. The ng-content selector is identical for all the rows when the ngFor duplicates the template which leaves me with only one ng-content transclusion point after rendering.
2. There is no reference to the row variable from the ngFor declaration in the <field-textbox> transcluded directives so I can't bind the data correctly.

Is there a better approach to implement the RepeaterComponent that would give me the least amount of effort to create more new MasterComponents of different arbitrary structures and different templates?

回答1:

You could use ngTemplateOutlet to achieve it.

Following are the steps in implementing dynamic repeater:

First step is to provide a TemplateRef as a child element of the RepeaterComponent:

<repeater [repeaterArray]="repeaterObj">
  <ng-template>
    ...
  </ng-template>
</repeater>

Second step is to query this template within RepeaterComponent via ContentChild:

export class RepeaterComponent { 
  @ContentChild(TemplateRef) itemTemplate: TemplateRef<any>;
  ...

Third step is use ngTemplateOutlet to render it template:

@Component({
  selector: 'repeater',
  template: `
    <input type="button" value="Add" (click)="addRow()">
    <div class="repeater" *ngFor="let row of repeaterArray">
        <div class="repeaterRow">
            <input type="button" value="Remove" (click)="removeRow(row.rowId)">
            <ng-template <== this line
                    [ngTemplateOutlet]="itemTemplate"
                    [ngTemplateOutletContext]="{ $implicit: row }">
                </ng-template>
        </div>
    </div>`
})
export class RepeaterComponent { 
  @Input() repeaterArray: Array<any>;
  @ContentChild(TemplateRef) itemTemplate: TemplateRef<any>;
  ...
}

Fourth step is to use reference to the row inside TemplateRef within MasterComponent (just back to our first step):

<repeater [repeaterArray]="repeaterObj">
  <template let-row>
    <field-textbox [data]="row.name" [label]="'Name'"></field-textbox>
    <field-textbox [data]="row.description" [label]="'Description'"></field-textbox>
  </template>
</repeater>

Notice: we are passing ngOutletContext like object with $implicit property.

using the key $implicit in the context object will set it's value as default.

It works as follows:

[ngTemplateOutletContext]="{ $implicit: row }"  ==> <template let-row>

[ngTemplateOutletContext]="{ item: row }"       ==> <template let-row="item">

ngOutletContext is availlable only since angular2 version of 2.0.0-rc.2

You could try the corresponding plunkr (updated to 5.0.0)