*ngIf else if in template
How would I have multiple cases in an *ngIf statement? I'm used to Vue or Angular 1 with having an if, else if, and else, but it seems like Angular 4 only has a true (if) and false (else) condition.
According to the documentation, I can only do:
<ng-container *ngIf="foo === 1; then first else second"></ng-container>
<ng-template #first>First</ng-template>
<ng-template #second>Second</ng-template>
<ng-template #third>Third</ng-template>
But I want to have multiple conditions (something like):
<ng-container *ngIf="foo === 1; then first; foo === 2; then second else third"></ng-container>
<ng-template #first>First</ng-template>
<ng-template #second>Second</ng-template>
<ng-template #third>Third</ng-template>
But I'm ending up having to use ngSwitch, which feels like a hack:
<ng-container [ngSwitch]="true">
<div *ngSwitchCase="foo === 1">First</div>
<div *ngSwitchCase="bar === 2">Second</div>
<div *ngSwitchDefault>Third</div>
</ng-container>
Alternately, it seems like a lot of the syntaxes I've got used to from Angular 1 and Vue aren't supported in Angular 4, so what would be the recommended way to structure my code with conditions like this?
Another alternative is to nest conditions
<ng-container *ngIf="foo === 1;else second"></ng-container>
<ng-template #second>
<ng-container *ngIf="foo === 2;else third"></ng-container>
</ng-template>
<ng-template #third></ng-template>
You can just use:
<ng-template [ngIf]="index == 1">First</ng-template>
<ng-template [ngIf]="index == 2">Second</ng-template>
<ng-template [ngIf]="index == 3">Third</ng-template>
unless the ng-container part is important to your design I suppose.
Here's a Plunker
if (index === 1) else if (foo === 2) which would have to be written if (index === 1) if (index !== 1 && foo === 2) which is a bit messy and more prone to errors, the more times we have to write inverse logic.
if (item === 'food' && kind === 'hamburger') {} else if (item === 'food' && kind === 'hotdog') {} else if (item === 'drink' && kind === 'beer') {} else if (item === 'drink' && kind === 'wine') {} else { /* could be poisonous */ }
NgTemplateOutlet with context like *ngTemplateOutlet="drink; context: beer", or maybe another component for categorizing.
This seems to be the cleanest way to do
if (foo === 1) {
} else if (bar === 99) {
} else if (foo === 2) {
} else {
}
in the template:
<ng-container *ngIf="foo === 1; else elseif1">foo === 1</ng-container>
<ng-template #elseif1>
<ng-container *ngIf="bar === 99; else elseif2">bar === 99</ng-container>
</ng-template>
<ng-template #elseif2>
<ng-container *ngIf="foo === 2; else else1">foo === 2</ng-container>
</ng-template>
<ng-template #else1>else</ng-template>
Notice that it works like a proper else if statement should when the conditions involve different variables (only 1 case is true at a time). Some of the other answers don't work right in such a case.
aside: gosh angular, that's some really ugly else if template code...
You can use multiple way based on sitaution:
If you Variable is limited to specific Number or String, best way is using ngSwitch or ngIf:
Note: You can choose any format, but notice every code has own problems
*ngIf="foo >= 7; then t7" instead of ... else t7.
foo >= 4 && foo <= 6; then t46; else t7 should work.
Or maybe just use conditional chains with ternary operator. if … else if … else if … else chain.
<ng-container [ngTemplateOutlet]="isFirst ? first : isSecond ? second : third"></ng-container>
<ng-template #first></ng-template>
<ng-template #second></ng-template>
<ng-template #third></ng-template>
I like this aproach better.
To avoid nesting and ngSwitch, there is also this possibility, which leverages the way logical operators work in Javascript:
<ng-container *ngIf="foo === 1; then first; else (foo === 2 && second) || (foo === 3 && third)"></ng-container>
<ng-template #first>First</ng-template>
<ng-template #second>Second</ng-template>
<ng-template #third>Third</ng-template>
you don't need to use *ngIf if you use ng-container
<ng-container [ngTemplateOutlet]="myTemplate === 'first' ? first : myTemplate ===
'second' ? second : third"></ng-container>
<ng-template #first>first</ng-template>
<ng-template #second>second</ng-template>
<ng-template #third>third</ng-template>
Angular is already using ng-template under the hood in many of the structural directives that we use all the time: ngIf, ngFor and ngSwitch. > What is ng-template in Angular https://www.angularjswiki.com/angular/what-is-ng-template-in-angular/
I came a cross this type of situation *ngIf elseIf else and I solved using ng-template, Hope the following snippet may depicts briefly,
I have a form control named "NIC" and need to show one error message at a time when the form control invalid.
form: FormGroup = new FormGroup({
NIC: new FormControl('', [Validators.required, Validators.minLength(10), Validators.maxLength(10), Validators.pattern("^[0-9]*$")])
});
Template
<mat-form-field appearance="standard">
<mat-label>NIC Number</mat-label>
<input matInput placeholder="Enter NIC no" formControlName="NIC">
<mat-error *ngIf="form.controls['NIC'].errors?.required; else minvalue">This field is mandatory.
</mat-error>
<ng-template #minvalue>
<mat-error *ngIf="form.controls['NIC'].errors?.minlength; else maxvalue">Minimum 10 charactors
needed.
</mat-error>
</ng-template>
<ng-template #maxvalue>
<mat-error *ngIf="form.controls['NIC'].errors?.maxLength; else numericonly">Maximum 10
charactors allowed.
</mat-error>
</ng-template>
<ng-template #numericonly>
<mat-error *ngIf="form.controls['NIC'].errors?.pattern">
Numeric characters only.
</mat-error>
</ng-template>
</mat-form-field>
You can also use this old trick for converting complex if/then/else blocks into a slightly cleaner switch statement:
<div [ngSwitch]="true">
<button (click)="foo=(++foo%3)+1">Switch!</button>
<div *ngSwitchCase="foo === 1">one</div>
<div *ngSwitchCase="foo === 2">two</div>
<div *ngSwitchCase="foo === 3">three</div>
</div>
*ngSwitchDefault directive would provide an "else" case.
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<ng-template #second *ngIf="foo === 2;else third">