title: I can't handle android back button on Ionic 4
body: <p>I am new on ionic development.I have tried more and more way by following articles.
  Finally I have tried on this <a href="https://stackoverflow.com/questions/51700879/handling-hardware-back-button-in-ionic3-vs-ionic4">Handling hardware back button in Ionic3 Vs Ionic4</a>
  Please help me <a href="https://stackoverflow.com/users/2422125/fabian-n"> @Fabian N. </a> </p>
  
  <p>But on device, I can't seem if the back button work regards code... that is the code is not work in my case. :(</p>
  
  <p>This is my ionic info.</p>
  
  <pre><code>Ionic:
  
     Ionic CLI                     : 5.2.3 (/usr/local/lib/node_modules/ionic)
     Ionic Framework               : @ionic/angular 4.6.2
     @angular-devkit/build-angular : 0.13.9
     @angular-devkit/schematics    : 7.3.9
     @angular/cli                  : 7.3.9
     @ionic/angular-toolkit        : 1.5.1
  
  Cordova:
  
     Cordova CLI       : 9.0.0 (cordova-lib@9.0.1)
     Cordova Platforms : android 8.0.0, ios 5.0.1
     Cordova Plugins   : cordova-plugin-ionic-keyboard 2.1.3, cordova-plugin-ionic-webview 4.1.1, (and 16 other plugins)
  
  Utility:
  
     cordova-res : not installed
     native-run  : 0.2.8 
  
  System:
  
     ios-deploy : 1.9.4
     ios-sim    : 8.0.1
     NodeJS     : v11.10.1 (/usr/local/bin/node)
     npm        : 6.7.0
     OS         : macOS Mojave
     Xcode      : Xcode 10.2 Build version 10E125
  </code></pre>
  
  <p>Already I have tried bellow event in <code>app.component.ts</code>. but I can't get any alert on real device when click back button.</p>
  
  <pre><code>1. Test case
    this.platform.backButton.subscribe(async () =&gt; {
       alert("Fired Back Button"); 
    });
  
  2. Test case
    this.platform.backButton.subscribe(() =&gt; {
       alert("Fired Back Button"); 
    });
  
  3. test case
    this.platform.backButton.subscribeWithPriority(0, () =&gt; {
       alert("Fired Back Button"); 
    });
  
  
  
  4. test case
    this.platform.backButton.subscribeWithPriority(100, () =&gt; {
       alert("Fired Back Button"); 
    });
  </code></pre>
  
  <p>In this case 4, I have tried such as priorities : 100, 101, 400, 999999. but I can't get any alert when click android back button.</p>
  
  <p>But the actually back button always pop pages.</p>
  
  <p>I just need to handle android hardware back button on my project.
  Please help me.
  Thank you in advance.
  Best Regards</p>