In developing an Angular app, I find myself using similar HTML components with the same arugments over and over. For example:
<fa-icon class="tms-hover-animation px-2" (click)="onDeleteContact(row)"
[icon]="faTrash" ngbTooltip="Delete Contact" placement="bottom auto" container="body">
The placement and container fields are redundantly defined over and over and over. What I'd much rather be able to do is the following:
<my-fa-icon (click)="onDeleteContact(row)" [icon]="faTrash"></my-fa-icon>
However,I can't find an minimal example of how to do this.
To clarify: my main misunderstanding is how can I reuse <fa-icon and pass all of its inputs (click, icon, etc... ) without having to explicitly redeclare them in my wrapper? Something like:
#Component
FaIconWrapper
args: <-- These automatically passed into underlying fa-icon
How could we create a custom HTML element like this with default arguments, but still pass (click), [icon] and any other inputs down into the wrapped component?
I'm also worried about falling into an anti-pattern here.
Related
I'm setting HTML returned from the API in my Angular component:
<div [innerHTML]="content"></div>
content in this example is something like this:
<table>
<tr>
<td>[audioPlayer:file.mp3]</td>
</tr>
</table>
Now I would like to inject the actual component inside the table cell.
If I make a certain container, I can create the component with createComponent:
audioPlayerComponentRef: ComponentRef<AudioPlayerComponent>;
#ViewChild('placeholder', { read: ViewContainerRef }) container;
const factory: ComponentFactory<AudioPlayerComponent> =
this.componentFactoryResolver.resolveComponentFactory(AudioPlayerComponent);
this.audioPlayerComponentRef = this.container.createComponent(factory);
Then I can inject it into a container in the template:
<div #placeholder></div>
However, going back to my original goal, I can't use such a container, as the component needs to be injected into a specific position into an innerHtml block.
I've been brainstorming all day, but I can't see any way to achieve this.
Generally speaking, this is contrary to the way Angular works. [innerHTML] is not parsed for any Angular functionality. No component selectors or even a ViewContainerRef can be found there. Rather, even remotely suspicious HTML, CSS and JS is removed as a security measure as Angular only trusts its own templates.
So InnerHTML is a no-go. But I was in the same boat myself and have written a library to solve this exact problem. With it, you can freely load dynamic components into strings without compromising security. If you're still stuck on this, you might wanna have a look at it.
I was following the tutorial Tour of Heroes. While adding a new hero they say
You can use an element paired with an add button.
Insert the following into the HeroesComponent template, after the heading:
<div>
<label for="new-hero">Hero name: </label>
<input id="new-hero" #heroName />
<!-- (click) passes input value to add() and then clears the input -->
<button type="button" class="add-button" (click)="add(heroName.value); heroName.value=''">
Add hero
</button>
</div>
Here I don't understand what is #heroName inside in input element (what is it called) and how does it help in pairing that input element with the button element.
Basically, what is that #<keyword> syntax within that input element. I know that it is not the id as that is already declared.
To answer the question, it's a reference to the input. You can find more details here:
https://angular.io/guide/template-reference-variables
Template variables help you use data from one part of a template in
another part of the template. Use template variables to perform tasks
such as respond to user input or finely tune your application's forms.
In the tutorial context, it's a reference to the input element. It helps to pair it with a button to be able to access it's value, without having to actually define a variable in the component.ts and trying to update the template directly. This help you "skip" a step, and actually have direct access to that value.
Template reference variables can become very handy in certain cases and are commonly used for example in angular material ( to call a function for a component )
<mat-menu #menuComponent ...></mat-menu>
<button (click)="menuComponent.close()"></button>
In the above example, you bind the menuComponent variable to "mat-menu" component, in which case you can access all the variables, public methods of such. In that case we can call "close" method from the mat-menu component.
Let me know if this is still unclear and I can try to give you more examples and explanation
In some instances, I need to just repeat some html code within my Template to DRY it up, but making a new component and passing a ton of props and dynamic data to it seems like overkill. Is there a way to define a repeatable block of template code that can just be reused?
A good example of this is my vuelidate validation error messages that are repeated. I don't want to create an entire vue component for them because then I need to pass in the validation, validation prop and a few other things so that seems like creating more complexity just to DRY up a little bit of the template.
I have this block of code on three different scenarious in the same template, is there a way I can just define them as a block to reuse. Literally nothing changes so it's very much against DRY principles.
<span
v-if="!$v.initialReplyText.required"
class="error">Your reply cannot be empty.</span>
<span
v-if="!$v.initialReplyText.maxLength"
class="error">Your reply cannot be over 2,000 characters.</span>
you can do dynamic binding using v-bind, that way you don't need to bind all properties individually.
<!-- pass down parent props in common with a child component -->
<child-component v-bind="$props"></child-component>
src: https://v2.vuejs.org/v2/api/#v-bind
You can also use slots, or scoped slots, which are commonly used for things like wrapping error messages in more complex markup.
If all elements are consecutively arranged as in your example, you can use v-for as below:
<span v-for="(criteria, msg) in {'Your reply cannot be empty.': !$v.initialReplyText.required, 'Your reply cannot be over 2,000 characters.': !$v.initialReplyText.maxLength }"
v-if="criteria" class="error">
{{msg}}
</span>
I have a problem with the new ng-content transclusion.
Let's say I have a component my-component that, in its ngOnInit() function does some heavy operation on load (for now, just a console.log()).
I have a wrapper, that displays the content via transclusion (my-wrapper.component.html).
<ng-content></ng-content>
If I set the surroundings up like this, the log statement doesn't show:
<my-wrapper *ngIf="false">
<my-component></my-component>
</my-wrapper>
I assume, the my-wrapper component does not get built, so the content is ignored.
But if I try to move the logic into the my-wrapper component like this (my-wrapper.component.html):
<ng-container *ngIf="false">
<ng-content></ng-content>
</ng-container>
I always see the console.log() output. I guess, the my-component gets built and then stored away until the *ngIf becomes true inside my-wrapper.
The intention was to build a generic "list-item + detail" component. Say I have a list of N overview-elements (my-wrapper), that get rendered in a *ngFor loop. Every of those elements has its own detail component (my-component) that is supposed to load its own data, once I decide to show more infos to a specific item.
overview.html:
<ng-container *ngFor="let item of items">
<my-wrapper>
<my-component id="item.id"></my-component>
</my-wrapper>
</ng-container>
my-wrapper.component.html:
<div (click)="toggleDetail()">Click for more</div>
<div *ngIf="showDetail">
<ng-content></ng-content>
</div>
Is there a way to tell Angular, to ignore the transcluded content until it is necessary to be added to the page? Analogously to how it was in AngularJS.
Based on the comment of #nsinreal I found an answer. I find it to be a bit abstruse, so I'm trying to post it here:
The answer is to work with ng-template and *ngTemplateOutlet.
In the my-wrapper component, set up the template like this (my-wrapper.component.html):
<div (click)="toggleDetail()">Click for more</div>
<div *ngIf="showDetail" [hidden]="!isInitialized">
<ng-container *ngTemplateOutlet="detailRef"></ng-container>
</div>
Note, that the [hidden] there is not really necessary, it hides the "raw" template of the child until it decides it is done loading. Just make sure, not to put it in a *ngIf, otherwise the *ngTemplateOutlet will never get triggered, leading to nothing happening at all.
To set the detailRef, put this in the component code (my-wrapper.component.ts):
import {Â ContentChild, TemplateRef } from '#angular/core';
#Component({ ... })
export class MyWrapperComponent {
#ContentChild(TemplateRef) detailRef;
...
}
Now, you can use the wrapper like this:
<my-wrapper>
<ng-template>
<my-component></my-component>
</ng-template>
</my-wrapper>
I am not sure, why it needs such complicated "workarounds", when it used to be so easy to do this in AngularJS.
By doing this:
<my-wrapper *ngIf="false">
<my-component></my-component>
</my-wrapper>
You are not calling MyComponent component, because the *ngIf is false. that means, that not calling it you are not instancing it and, therefore, not passing through its ngOnInit. And that's why you are not getting the console log.
By doing this:
<ng-container *ngIf="false">
<ng-content></ng-content>
</ng-container>
You are inside the component, you are just limiting what to render in your template, but you already instanced your component and, therefore, you passed through your ngOnInit and you get your console log done.
If, you want to limit something (component call with selector or a ng-content or even a div) until you have some data available, you can do the following:
datasLoaded: Promise<boolean>;
this.getData().subscribe(
(data) => {
this.datasLoaded = Promise.resolve(true); // Setting the Promise as resolved after I have the needed data
}
);
And in your template:
<ng-container *ngIf="datasLoaded | async">
// stuff here
</ng-container>
Or:
<my-component *ngIf="datasLoaded | async">
// Didn't test this one, but should follow the same logic. If it doesn't, wrap it and add the ngIf to the wrapper
</my-component>
It’s because Ng content happens at the build time and when you pass the content it is actually not removed or recreated with the ngIf directive. It is only moved and the component is instantiated .
I encountered this problem recently as well but settled on a different solution than the currently accepted one.
Solution (TL;DR)
(Solution is for AngularDart; I figure it's similar in Angular though)
Use a structural directive; tutorials linked below.
Instead of:
<my-wrapper>
<my-contents></my-contents>
</my-wrapper>
your usage becomes:
<div *myWrapper>
<my-contents></my-contents>
</div>
which is shorthand for the following (in AngularDart; I think Angular uses <ng-template>)
<template myWrapper>
<div>
<my-contents></my-contents>
</div>
</template>
The MyWrapper directive logic is similar to NgIf except it has its own logic to compute the condition. Both of the following tutorials explain how to create an NgIf-like directive and how to pass it your own inputs using the special microsyntax (e.g. *myWrapper="myInput: expression"). Note that the microsyntax doesn't support outputs (#Output), but you can mimic an output by using an input that is a function.
Tutorial for Angular
Tutorial for AngularDart
Caveat: Since this is just a directive, it shouldn't do anything more complicated than instantiating a template ref at the appropriate time and maybe specifying some DI providers. For example, I would avoid trying to apply styles or instantiating a complex tree of components in the directive. If I wanted to create a list component, I would probably take the #ContentChild(TemplateRef) approach described in another answer; you would lose the asterisk shorthand for creating <template> but you would gain the full power of components.
My problem
My team owns an app that's part of a larger web application with other apps owned by other teams. Our components assume they can inject a MyAppConfiguration object, but this object can only be injected after it is loaded with an asynchronous request. In our app this is not a problem: we have a "shell" component that hides everything behind an ngIf until the configuration is loaded.
The problem is when other teams want to reference our components. We don't want them to duplicate the "wait until configuration is loaded" logic every time, so I tried creating a wrapper component that can be used like so:
<my-app-wrapper>
<my-app-component></my-app-component>
</my-app-wrapper>
The wrapper injects a service object and hides its contents behind an ngIf until the service says that the configuration is loaded.
Like the question poster, I discovered that the ng-content approach doesn't work as intended: while the contents are correctly hidden from the DOM, Angular still instantiates the components causing dependency injection to fail.
The solution that I settled on was to rewrite the wrapper component as a structural directive.
I have a component (let's call it ListComponent) whose purpose is to edit a list. It allows the user to add, delete, and reorder elements. Its template looks something like this:
<div> <!-- Some Buttons --> </div>
<ul>
<li *ngFor="element in dataArray">
<string-editor [(NgModel)]=element></string-editor>
<!-- More Buttons -->
</li>
</ul>
The <string-editor> is also a custom component with a template that is basically just an input component with a bit of styling. What I want to be able to do is have multiple versions of ListComponent that can handle different types of data (e.g. numbers, custom objects with multiple fields.) To do this, I would like to be able to replace <string-editor> in the template with another component class (like <number-editor> or <my-custom-object-editor>.) They would all support NgModel. I have looked into dynamic component creation, but it appears that there is no way I can use it with *ngFor's change detection.
So, in summary, is there a way to change <string-editor> to another tag programmatically? If not, is there a way that I can use dynamic component creation with *ngFor's change detection?
What you can do is.
Use a ng switch if u can determine what type of component you need to use. Or You can also write a Ng if else
NgSwitch https://angular.io/api/common/NgSwitch
ng if else https://angular.io/api/common/NgIf