How to make a if-else Angular template with only ng-container?

Question

I would like to make an if-else statement in my angular template. I started with that :

<ng-container *ngIf="contributeur.deb; else newDeb" >
    [... HERE IS A RESULT 1]
</ng-container>
<ng-template #newDeb>
    [... HERE IS A RESULT 2]
</ng-template>

And I tried to only use ng-container :

<ng-container *ngIf="contributeur.deb; else newDeb" >
    [... HERE IS A RESULT 1]
</ng-container>
<ng-container #newDeb>
    [... HERE IS A RESULT 2]
</ng-container >

Unfortunately, this does not work. I have this error :

ERROR TypeError: templateRef.createEmbeddedView is not a function
    at ViewContainerRef_.createEmbeddedView (eval at <anonymous> (vendor.bundle.js:11), <anonymous>:10200:52)
    at NgIf._updateView (eval at <anonymous> (vendor.bundle.js:96), <anonymous>:2013:45)
    at NgIf.set [as ngIfElse] (eval at <anonymous> (vendor.bundle.js:96), <anonymous>:1988:18)
    at updateProp (eval at <anonymous> (vendor.bundle.js:11), <anonymous>:11172:37)
    at checkAndUpdateDirectiveInline (eval at <anonymous> (vendor.bundle.js:11), <anonymous>:10873:19)
    at checkAndUpdateNodeInline (eval at <anonymous> (vendor.bundle.js:11), <anonymous>:12290:17)
    at checkAndUpdateNode (eval at <anonymous> (vendor.bundle.js:11), <anonymous>:12258:16)
    at debugCheckAndUpdateNode (eval at <anonymous> (vendor.bundle.js:11), <anonymous>:12887:59)
    at debugCheckDirectivesFn (eval at <anonymous> (vendor.bundle.js:11), <anonymous>:12828:13)
    at Object.eval [as updateDirectives] (ActionsButtons.html:5)

Can anyone explain me what is going wrong in this code ?

score 98 · Accepted Answer · answered May 31 '17 at 15:02

98

The code for the ngIf directive expects to be passed a reference to a template (TemplateRef) for the else branch, which it will call createEmbeddedView on to display the nested content. Therefore, it makes no sense to try to use any other kind of element for the else content - it just won't work. You're able to nest an ng-container inside the ng-template if needs be, though.

This might seem unintuitive, but bear in mind that structural directives (i.e. ones that you call with a *) are always represented as ng-template under the hood, no matter what kind of element they're attached to - these two pieces of code are the same:

<ng-container *ngIf="contributeur.deb; else newDeb" >
    ...
</ng-container>
<ng-template #newDeb>
    ...
</ng-template>

<ng-template [ngIf]="contributeur.deb; else newDeb">
    <ng-container>
        ...
    </ng-container>
</ng-template>
<ng-template #newDeb>
    ...
</ng-template>

answered May 31 '17 at 15:02

Joe Clay

33,401
4
85
85

I'd recommend reading the [Angular docs page](https://angular.io/docs/ts/latest/guide/structural-directives.html) on Structural Directives - it's long, but really informative. – Joe Clay May 31 '17 at 15:21
I cannot thank you enough for this answer. I spent hours scratching my head trying to solve a null component in a canDeactivate guard. – tpdietz Aug 04 '20 at 04:49
@JoeClay Error: src/app/leads/leads-list.component.ts:99:34 - error NG5002: Parser Error: Binding expression cannot contain chained expression at column 7 in [lead; else newDeb] in C:/Users/iii/Desktop/ui-code-challenge-1-master/src/app/leads/leads-list.component.ts@98:33 99 – CarinaCase Jul 01 '21 at 21:41

score 18 · Answer 2 · answered Nov 29 '19 at 14:55

I do not love the standard Angular structure for if then else. Then I found an alternative solution with ngSwitch:

<ng-container [ngSwitch]="isFirstChoice(foo) ? 1 : (isSecondChoice(foo) ? 2 : -1)">
  <ng-container *ngSwitchCase="1">
    ...first choice...
  </ng-container>
  <ng-container *ngSwitchCase="2">
    ...second choice...
  </ng-container>
  <ng-container *ngSwitchDefault>
    ...another choice...
  </ng-container>
</ng-container>

To answer to your request I'd use this:

<ng-container [ngSwitch]="contributeur.deb && 'isDeb'">
  <ng-container *ngSwitchCase="'isDeb'">
    ......
  </ng-container>
  <ng-container *ngSwitchDefault>
    ......
  </ng-container>
</ng-container>

score 6 · Answer 3 · answered Oct 22 '21 at 23:44

It bears mentioning that this simple alternative is perhaps more readable than many of the other options. Just using a second ng-container, and just 'not'-ing the condition with an exclamation mark to make the else section.

<ng-container *ngIf="contributeur.deb" >
    [... HERE IS A RESULT 1]
</ng-container>
<ng-container *ngIf="!contributeur.deb">
    [... HERE IS A RESULT 2]
</ng-container >

How to make a if-else Angular template with only ng-container?

3 Answers3