How to have if condition for css class?

Question

When editing my component, the column grids also are changed.

Currently, I have this for my edit-component.html

      <div class="col-6" *ngIf="!edit">
        Column1
      </div>
      <div class="col-12 col-md-4 col-sm-2" *ngIf="edit">
        Column1
      </div>
      <div class="col-6" *ngIf="!edit">
        Column2
      </div>
      <div class="col-12 col-md-4 col-sm-2" *ngIf="edit">
        Column2
      </div>

And I have this for edit-component.ts

    edit: boolean = false;

This method works and the css is changing when editting or readonly. But is there other way that I can have if condition for col-12 col-md-5 and col-6?

allthings dev · Accepted Answer · 2024-12-21 15:25:28Z

2

You can use the ngClass directive.

<div [ngClass]="{'col-6': !edit, 'col-sm-2 col-md-4 col-12': edit}">
    Column1
</div>

edited Dec 21, 2024 at 15:25

allthings dev

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answered May 16, 2022 at 20:46

spots

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4 Comments

mfaith Over a year ago

The only adjustment I'd suggest, is to extract that out to a getter, so that you can take advantage of re-use. Having that defined on every column element will be a mess.

spots Over a year ago

Fair point about re-use, however I wouldn't use a getter here because they're executed whenever angular runs change detection. Since this def would make the template harder to read, I'd actually consider extracting this into a pipe. Which also makes it more testable.

newProgrammer005 Over a year ago

ngClass directive is the way. I just edited how it looks but it works when using ngClass like [ngClass]="edit ? 'col-12 col-md-4 col-sm-2' : 'col-6'"

mfaith Over a year ago

@newProgrammer005 that works, just because it works with simple strings. But the more powerful way of using ngClass involves creating an object like this, so that you can dynamically apply n number of classes based on different conditions. This illustrates that capability more. You may also consider the approach I suggested below, which allows for better re-use.

mfaith · Accepted Answer · 2022-05-16 20:51:35Z

0

Yes. Using the NgClass directive, you can apply classes dynamically based on conditions in your typescript class.

For example: Typescript:

get columnClassDef() {
  return {
    'col-6': !this.edit,
    'col-12 col-md-4 col-sm-2': this.edit,
  };
}

Html:

<div [ngClass]="columnClassDef">
  Column1
</div>
<div [ngClass]="columnClassDef">
  Column2
</div>

NgClass will apply the key of the object as a css class on the element, if the value evaluates to true. It doesn't add the class if the value evaluates to false.

answered May 16, 2022 at 20:51

mfaith

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3 Comments

spots Over a year ago

This definitely makes the template more readable, but getColumnClassDef will be re-executed with every change detection cycle.

mfaith Over a year ago

@spots It would if it was inline in the template, though, too, wouldn't it? I think a pure pipe is the only way around that.

spots Over a year ago

TBH, I'm not sure. The edit variable is the only thing that needs to be evaluated, so I guess technically yes there's work being done. In this example however a new object is created every time. It's unlikely to create a problem in small apps, but once there's lots of components angular has to manage it could become death by papercuts! Like you said, a pure pipe is def the way to go IMO.

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