let currentUid=this.afAuth.auth.currentUser.uid.valueOf();
    this.items = afDB.list('ToDoList/'+currentUid).valueChanges();
    this.items.subscribe((data)=>{
      console.log(""+ data);
      this.tasks = data;

checked($event){
    if(event.target.checked==true)
    {

    }
    else
    {

    }
  }

<ion-item class="text" *ngFor="let task of tasks">
          <input type="checkbox" (change)="checked($event,task)"/>