angular2 custom directives inputs syntax - html

Question

I create a custom directive and set the selector value to be "[unless-directive]".
The directive get a Boolean and use it to change the view as so:
import {Directive, TemplateRef, ViewContainerRef} from 'angular2/core';
#Directive({
selector: '[unless-directive]',
inputs: ['givenBoolean : myDirectiveFunction']
})
export class UnlessDirective {
private _templateRef: TemplateRef;
private _viewContainerRef: ViewContainerRef;
constructor(_templateRef: TemplateRef, _viewContainerRef: ViewContainerRef) {
this._templateRef = _templateRef;
this._viewContainerRef = _viewContainerRef;
}
set myDirectiveFunction(condition: boolean) {
!condition ? this._viewContainerRef.createEmbeddedView(this._templateRef)
: this._viewContainerRef.clear();
}
}
In my template I tried to pass the condition like so:
<div name="customDirective">
<h2>Custom Directive</h2>
<div>
Enter true or false:
<br/>
<input type="text" #condition (keyup)="0"/>
<div *unless-directive [givenBoolean]="condition.value != 'false'">
Only shown if 'false' wad enterded!
</div>
</div>
</div>
When I running the code I get this error:
EXCEPTION: Template parse errors: Can't bind to 'givenBoolean' since
it isn't a known native property (" ... Only shown if 'false' wad enterded!"): StructualDirectivesComponent#47:39
I guess my syntax is wrong, but I can't find where or why?
I looked it up on Angular2 Docs, but the example use the same name for the input and the selector, the thing that I'm trying to avoid.
Can anyone know a better way or can find my syntax problem?
Thanks.

Answer 1

The * prefix syntax is only a syntatic sugar. It expands the directive declaration.
The * prefix syntax is a convenient way to skip the <template> wrapper tags and focus directly on the HTML element to repeat or include. Angular sees the * and expands the HTML into the <template> tags for us.
This is documented in * and <template> and Directive decorator/Lifecycle hooks.
So, in your case, the [givenBoolean] property is not expected to be in the directive. In other words, this:
<div *unless-directive [givenBoolean]="condition.value != 'false'">
Only shown if 'false' wad enterded!
</div>
Becomes, actually:
<template [unless-directive]="">
<div [givenBoolean]="condition.value != 'false'">
Only shown if 'false' wad enterded!
</div>
</template>
And since givenBoolean is not a property in the component (not the directive), the error appears.
So if you want custom behavior, I suggest you experiment using the expanded version and only after it works you go to the * syntax, it will be simpler to reason about.