Cant resolve all parameters - firebase

Question

Hi I am building a toDo app and i ran into this problem after i completed all of the steps.
error---
Runtime Error
Can't resolve all parameters for TaskListPage: ([object Object], ?).
Stack
import { Component } from '#angular/core';
import { NavController, ItemSliding } from 'ionic-angular';
import {Task} from './task';
import {AngularFire, FirebaseListObservable} from 'angularfire2';
#Component({
selector: 'page-tasklist',
templateUrl: 'tasklist.html'
} )
export class TaskListPage {
tasks: FirebaseListObservable <any[]>;
constructor(public navCtrl: NavController, af: AngularFire) {
this.tasks = af.database.list('/tasks');
}
addItem() {let theNewTask: string = prompt("New Task");
if (theNewTask !== '')
{ this.tasks.push({ title: theNewTask, status: 'open'});
}
}
markAsDone( slidingItem: ItemSliding, task: Task)
{ this.tasks.update(task.$key, {status: 'done'});
slidingItem.close();
}
removeTask(slidingItem: ItemSliding, task: Task)
{ this.tasks.remove(task.$key);
slidingItem.close();
}
}

Answer 1

This is a place where Angular can really improve its error messaging. The offending line is this one:
constructor(public navCtrl: NavController, af: AngularFire) {
You have no access modifier on the af variable, so it is assumed to be a call-time variable (no public, protected or private, so Angular does not know it is supposed to be a class member variable). Since at compile time, what af will be is not known, it results in that warning.
The simple solution is: add an access modifier on the variable. If it is not meant to be shared, private is usually the appropriate modifier.
Also, AngularFire does not look like a valid export from angularfire2. It looks like it should be either AngularFirestore or one of the functionality specific modules - auth, messaging, etc. Also make sure you have set up your AngularFireModule in your app.module, by following the setup directions in their repo.