Angular 2 Ngif Not Refreshing When Variable Update From Oberservable Subscribe

When working with Angular, you might come across a situation where the `*ngIf` directive does not refresh as expected even when a variable updates through an observable subscription. This issue can be frustrating, especially when you are trying to build dynamic and interactive web applications. But fear not! In this article, we will dive into the common reasons why this problem occurs and explore some solutions to ensure that your Angular application behaves as intended.

### Understanding the Issue
At the core of this problem is the Asynchronous nature of Observables in Angular. Observables are used for handling data streams and are often asynchronous, which means that the data they emit might arrive at a different time than expected. When you update a variable coming from an Observable subscribe method, Angular might not detect the change immediately, leading to the `*ngIf` directive not refreshing as you would expect.

### Solutions to the Problem
1. NgZone Service: Angular provides the `NgZone` service to explicitly trigger change detection within a certain zone. You can inject `NgZone` into your component and run the change detection manually after updating the variable. This ensures that Angular picks up the changes and updates the view accordingly.

import { NgZone } from '@angular/core';

constructor(private zone: NgZone) {}

// Inside your Observable subscription
this.zone.run(() => {
  // Update your variable here
});

2. ChangeDetectorRef: Another way to tackle this issue is by using the `ChangeDetectorRef` service, which allows you to manually mark the component and its children for change detection. After updating the variable, you can call the `detectChanges` method to trigger the change detection process.

import { ChangeDetectorRef } from '@angular/core';

constructor(private cdr: ChangeDetectorRef) {}

// Inside your Observable subscription
// Update your variable
this.cdr.detectChanges();

3. Immutable Data: When dealing with Observables, prefer using immutable data structures or objects. By creating a new reference when updating the variable instead of mutating the existing object, you ensure that Angular detects the changes correctly. This can help in avoiding issues with change detection not being triggered.

### Debugging Tips
- Console Logging: Add console logs before and after updating the variable in your Observable subscription to ensure that the value is changing as expected.
- Check Change Detection Strategy: Verify the change detection strategy set for your component. If it is set to `OnPush`, you might need to manually trigger change detection after updating the variable.

By following these tips and solutions, you can effectively manage the issue of `*ngIf` not refreshing when a variable updates from an Observable subscription in Angular. Remember, understanding the asynchronous nature of Observables and taking advantage of tools like `NgZone` and `ChangeDetectorRef` will help you streamline your Angular development workflow. Happy coding!