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Angular - input formControl limit max length
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<!-- | |
使用[inputlimit], 可以使用默认值。 | |
使用[inputlimit]="2", 可以设置要check的长度。 | |
note that: 不能直接使用 inputlimit或inputlimit="2" 会导致默认值为空或是字符串类型。 | |
--> | |
<input type="text" [inputlimit]="2" formControlName="name" /> |
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import { | |
Directive, | |
ElementRef, | |
Input, | |
HostListener, | |
Renderer2, | |
forwardRef, | |
} from '@angular/core'; | |
import { DefaultValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms'; | |
@Directive({ | |
selector: '[inputlimit]', | |
providers: [ | |
{ | |
provide: NG_VALUE_ACCESSOR, | |
useExisting: forwardRef(() => InputLimitDirective), | |
multi: true, | |
}, | |
], | |
}) | |
export class InputLimitDirective extends DefaultValueAccessor { | |
@Input() inputlimit: number = 3; | |
constructor(renderer: Renderer2, elementRef: ElementRef) { | |
super(renderer, elementRef, true); | |
} | |
@HostListener('input', ['$event.target.value']) | |
public input(event: string) { | |
if (event.length > this.inputlimit) { | |
const transformed = event.substring(0, this.inputlimit); | |
super.writeValue(transformed); | |
this.onChange(transformed); | |
} | |
} | |
public writeValue(value: string) { | |
window.requestAnimationFrame(() => { | |
this.input(value); | |
}); | |
} | |
} |
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