how to stop ngOnChanges Called before ngOnInit()

Question

In my angular application, i came up with a situation where ngOnchanges should only be called when the inputs are bound to changes. so, is there a way to stop the execution of ngOnChanges before ngOnInit. Is there a way to accomplish this. Thanks in Advance.

Answer 1

You cannot prevent this behavior, but you can:

Use a Subject :

class Foo implements OnChanges,OnInit,OnDestroy{    onChanges = new Subject<SimpleChanges>();    ngOnInit(){     this.onChanges.subscribe((data:SimpleChanges)=>{       // only when inited     });   }   ngOnDestroy(){     this.onChanges.complete();   }    ngOnChanges(changes:SimpleChanges){     this.onChanges.next(changes);   }  } 

Use a boolean property:

class Foo implements OnChanges,OnInit{    initialized=false;    ngOnInit(){     // do stuff     this.initialized = true;   }    ngOnChanges(changes:SimpleChanges){     if(this.initialized){       // do stuff when ngOnInit has been called     }   }  } 

Use the SimpleChanges API

You can also check the SimpleChange.isFirstChange() method :

isFirstChange() : boolean Check whether the new value is the first value assigned.

class Foo implements OnChanges,OnInit{    @Input()   bar:any;    ngOnInit(){     // do stuff   }    ngOnChanges(changes:SimpleChanges){     if(!changes["bar"].isFirstChange()){       // do stuff if this is not the initialization of "bar"     }   }  }