问题
What is wrong with my Angular code? I am getting:
Cannot read property \'remove\' of undefined at BrowserDomAdapter.removeClass ...
HTML
<ol class=\"breadcrumb\">
<li *ngClass=\"{active: step===\'step1\'}\" (click)=\"step=\'step1; \'\">Step1</li>
<li *ngClass=\"{active: step===\'step2\'}\" (click)=\"step=\'step2\'\">Step2</li>
<li *ngClass=\"{active: step===\'step3\'}\" (click)=\"step=\'step3\'\">Step3</li>
</ol>
回答1:
Angular 2,..,7 provides several ways to add classes conditionally:
type one
[class.my-class]="step=='step1'"
type two
[ngClass]="{'my-class': step=='step1'}"
and multiple option:
[ngClass]="{'my-class': step=='step1', 'my-class2':step=='step2' }"
type three
[ngClass]="{1:'my-class1',2:'my-class2',3:'my-class4'}[step]"
type four
[ngClass]="(step=='step1')?'my-class1':'my-class2'"
回答2:
[ngClass]=... instead of *ngClass.
* is only for the shorthand syntax for structural directives where you can for example use
<div *ngFor="let item of items">{{item}}</div>
instead of the longer equivalent version
<template ngFor let-item [ngForOf]="items">
<div>{{item}}</div>
</template>
See also https://angular.io/docs/ts/latest/api/common/index/NgClass-directive.html
<some-element [ngClass]="'first second'">...</some-element> <some-element [ngClass]="['first', 'second']">...</some-element> <some-element [ngClass]="{'first': true, 'second': true, 'third': false}">...</some-element> <some-element [ngClass]="stringExp|arrayExp|objExp">...</some-element> <some-element [ngClass]="{'class1 class2 class3' : true}">...</some-element>
See also https://angular.io/docs/ts/latest/guide/template-syntax.html
<!-- toggle the "special" class on/off with a property --> <div [class.special]="isSpecial">The class binding is special</div> <!-- binding to `class.special` trumps the class attribute --> <div class="special" [class.special]="!isSpecial">This one is not so special</div>
<!-- reset/override all class names with a binding --> <div class="bad curly special" [class]="badCurly">Bad curly</div>
回答3:
Another solution would be using [class.active].
Example :
<ol class="breadcrumb">
<li [class.active]="step=='step1'" (click)="step='step1'">Step1</li>
</ol>
回答4:
That's the normal structure for ngClass is:
[ngClass]="{'classname' : condition}"
So in your case, just use it like this...
<ol class="breadcrumb">
<li [ngClass]="{'active': step==='step1'}" (click)="step='step1'">Step1</li>
<li [ngClass]="{'active': step==='step2'}" (click)="step='step2'">Step2</li>
<li [ngClass]="{'active': step==='step3'}" (click)="step='step3'">Step3</li>
</ol>
回答5:
with the following examples you can use 'IF ELSE'
<p class="{{condition ? 'checkedClass' : 'uncheckedClass'}}">
<p [ngClass]="condition ? 'checkedClass' : 'uncheckedClass'">
<p [ngClass]="[condition ? 'checkedClass' : 'uncheckedClass']">
回答6:
You can use ngClass to apply the class name both conditionally and not in Angular
For Example
[ngClass]="'someClass'">
Conditional
[ngClass]="{'someClass': property1.isValid}">
Multiple Condition
[ngClass]="{'someClass': property1.isValid && property2.isValid}">
Method expression
[ngClass]="getSomeClass()"
This method will inside of your component
getSomeClass(){
const isValid=this.property1 && this.property2;
return {someClass1:isValid , someClass2:isValid};
}
回答7:
You should use something ([ngClass] instead of *ngClass) like that:
<ol class="breadcrumb">
<li [ngClass]="{active: step==='step1'}" (click)="step='step1; '">Step1</li>
(...)
回答8:
In Angular 7.X
The CSS classes are updated as follows, depending on the type of the expression evaluation:
string - the CSS classes listed in the string (space delimited) are added
Array - the CSS classes declared as Array elements are added
Object - keys are CSS classes that get added when the expression given in the value evaluates to a truthy value, otherwise they are removed.
<some-element [ngClass]="'first second'">...</some-element>
<some-element [ngClass]="['first', 'second']">...</some-element>
<some-element [ngClass]="{'first': true, 'second': true, 'third': false}">...</some-element>
<some-element [ngClass]="stringExp|arrayExp|objExp">...</some-element>
<some-element [ngClass]="{'class1 class2 class3' : true}">...</some-element>
回答9:
While I was creating a reactive form, I had to assign 2 types of class on the button. This is how I did it:
<button type="submit" class="btn" [ngClass]="(formGroup.valid)?'btn-info':''"
[disabled]="!formGroup.valid">Sign in</button>
When the form is valid, button has btn and btn-class (from bootstrap), otherwise just btn class.
回答10:
to extend MostafaMashayekhi his answer for option two> you can also chain multiple options with a ','
[ngClass]="{'my-class': step=='step1', 'my-class2':step=='step2' }"
Also *ngIf can be used in some of these situations usually combined with a *ngFor
class="mats p" *ngIf="mat=='painted'"
回答11:
ngClass syntax:
[ngClass]="{'classname' : conditionFlag}"
You can use like this:
<ol class="breadcrumb">
<li [ngClass]="{'active': step==='step1'}" (click)="step='step1'">Step1</li>
<li [ngClass]="{'active': step==='step2'}" (click)="step='step2'">Step2</li>
<li [ngClass]="{'active': step==='step3'}" (click)="step='step3'">Step3</li>
</ol>
回答12:
This is what worked for me:
[ngClass]="{'active': dashboardComponent.selected_menu == 'profile'}"
回答13:
Let, YourCondition is your condition or a boolean property, then do like this
[class.yourClass]="YourCondition"
回答14:
Additionally, you can add with method function:
In HTML
<div [ngClass]="setClasses()">...</div>
In component.ts
// Set Dynamic Classes
setClasses() {
let classes = {
constantClass: true,
'conditional-class': this.item.id === 1
}
return classes;
}
回答15:
Not relevant with [ngClass] directive but I was also getting the same error as
Cannot read property 'remove' of undefined at...
and I thought to be the error in my [ngClass] condition but it turned out the property I was trying to access in the condition of [ngClass] was not initialized.
Like I had this in my typescript file
element: {type: string};
and In my [ngClass] I was using
[ngClass]="{'active', element.type === 'active'}"
and I was getting the error
Cannot read property 'type' of undefined at...
and the solution was to fix my property to
element: {type: string} = {type: 'active'};
Hope it helps somebody who is trying to match a condition of a property in [ngClass]
来源：https://stackoverflow.com/questions/35269179/angular-conditional-class-with-ngclass