I am currently utilizing Angular 2.
At the moment, I have two @input variables named aa and bb. My objective is:
aa changes, perform a specific action.bb changes, execute a different action.How can I identify which @Input has changed within the ngOnChanges method? Thank you
@Input() aa;
@Input() bb;
ngOnChanges(changes: { [propName: string]: SimpleChange }) {
// if aa changes, do something
// if bb changes, do other thing
}One possible solution could be implemented in the following manner
ngOnChanges(changes: { [propName: string]: SimpleChange }) {
if( changes['aa'] && changes['aa'].previousValue != changes['aa'].currentValue ) {
// aa property has changed
}
if( changes['bb'] && changes['bb'].previousValue != changes['bb'].currentValue ) {
// bb property has changed
}
}
It is surprising to see the unchanged properties being defined. According to the cookbook, I would anticipate only the changed properties to be defined.
Link to further information on parent to child communication with ngOnChanges
If the above approach seems too verbose, an alternative method using setters can also be tried:
_aa: string;
_bb: string;
@Input() set aa(value: string) {
this._aa = value;
// perform actions when 'aa' changes
}
@Input() set bb(value: string) {
this._bb = value;
// perform actions when 'bb' changes
}
Link to more details on parent to child communication using setter methods
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