How to pass context to Angular 5 template from *ngIf

Question

Angular's NgTemplateOutlet allows you to pass a context to the outlet for property binding.

<ng-container *ngTemplateOutlet="eng; context: {$implicit: 'World'}"></ng-container>
<ng-template #eng let-name><span>Hello {{name}}!</span></ng-template>

Angular's *ngIf allows you to embed one template or another based on a boolean condition:

<ng-container *ngIf="isConditionTrue; then one else two"></ng-container>
<ng-template #one>This shows when condition is true</ng-template>
<ng-template #two>This shows when condition is false</ng-template>

How can I pass context to these templates referred to within the *ngIf syntax?

Answer 1

Actually you can input your condition into ngTemplateOutlet (and get rid of ngIf).

<ng-container *ngTemplateOutlet="condition ? template1 : template2; context: {$implicit: 'World'}">
</ng-container>

Answer 2

The accepted answer works when you have a single expression but will get complex where you have multiple ngIf expressions and templates.

A full example for cases where you have multiple expressions, resulting templates and even different context variables:

<!-- Example ngFor -->
<mat-list-item
    *ngFor="let location of locations$; let l = index"
    [ngSwitch]="location.type"
    >
    <!-- ngSwitch could be ngIf on each node according to needs & readability -->

    <!-- Create ngTemplateOutlet foreach switch case, pass context -->
    <ng-container *ngSwitchCase="'input'">
        <ng-container 
            *ngTemplateOutlet="inputField; context: { location: location, placeholder: 'Irrigation Start', otherOptions: 'value123' }">
        </ng-contaier>
    </ng-container>

    <ng-container *ngSwitchCase="'select'">
        <ng-container 
            *ngTemplateOutlet="selectField; context: { location: location, selectSpecificOptions: 'scope.someSelectOptions' }">
        </ng-contaier>
    </ng-container>

    <!-- ngSwitchCase="'others'", etc. -->

</mat-list-item>



<!-- Shared ngTemplates & note let-[variable] to read context object into scope -->
<ng-template 
    #inputField 
    let-location="location"
    let-placeholder="placeholder
    let-otherOptions="otherOptions"
    <!-- Context is now accessible using let-[variable] -->
    INPUT: {{ location.value }} {{ placeholder }} {{ otherOptions }}
</ng-template>

<ng-template 
    #selectField 
    let-location="location"
    let-options="selectSpecificOptions"
    <!-- Context is now accessible using let-[variable] -->
    SELECT: {{ location.value }} {{ options }}
</ng-template>

Where;

location$ = [
    {type: 'input',  value: 'test'}, 
    {type: 'input',  value: 'test 2'}, 
    {type: 'select', value: 'test 3'}
]; 

Answer 3

Why not just do this:

<ng-container *ngIf="isConditionTrue; else two">
 // your first template, #one, goes here.
</ng-container>

<ng-template #two>
 // your second template, #two goes here.
</ng-template>