<ng-template> </ ng-template>正在加载多次

Question

I am using ngTemplateOutlet to load . but It loads a template multiple times .It is loading correct template but it executing multiple times loadTemplate() method.

In HTML :

<table>
    <thead>
    </thead>
    <tbody>
        <ng-template [ngTemplateOutlet]="loadTemplate()"></ng-template>
    </tbody>
</table>

<ng-template #template1>
    <tr *ngFor="iteration">
        <p>Hiii</p>
    </tr>
</ng-template>

<ng-template #template2>
    <tr *ngFor="iteration">
        <p>Byee</p>
    </tr>
</ng-template>

In my component.ts :

@ViewChild('template1') template1: TemplateRef<any>;
@ViewChild('template1') template1: TemplateRef<any>;
loadTemplate(){
    if (condition)
        return this.template1;

    return this.template2;
}

Answer 1

[ngTemplateOutlet]="loadTemplate()"

causes loadTemplate() to be called every time change detection runs.

Rather assign the result of loadTemplate() to a field and use that field in binding

[ngTemplateOutlet]="myTemplate"

then change detection and the ngTemplateOutlet directive can see that there was no change and won't re-initialize the template.

Answer 2

Another approach would be:

<table>
    <thead>
    </thead>
    <tbody>
        <ng-template [ngTemplateOutlet]="condition ? template1 : template2"></ng-template>
    </tbody>
</table>

<ng-template #template1>
    <tr *ngFor="iteration">
        <p>Hiii</p>
    </tr>
</ng-template>

<ng-template #template2>
    <tr *ngFor="iteration">
        <p>Byee</p>
    </tr>
</ng-template>