break down observer for resolution angular code example

Example: angular cdk media query

import { Component, OnInit } from '@angular/core';
import { BreakpointObserver, BreakpointState } from '@angular/cdk/layout';

@Component({ ... })
export class AppComponent implements OnInit {
  public showContainer: boolean;
  constructor(public breakpointObserver: BreakpointObserver) {}

  ngOnInit() {
    this.breakpointObserver
      .observe(['(min-width: 400px)'])
      .subscribe((state: BreakpointState) => {
        if (state.matches) {
          this.showContainer = true;
        } else {
          this.showContainer = false;
        }
      });
  }
}