[feat] Custom back button/gesture behavior on Android

[dacid44]

Describe the problem

Currently, on Tauri v2, if the back button or gesture is used on Android, and the app is a single page app (e.g., manages everything on the same page without managing custom history), the app just closes.

Describe the solution you'd like

I would like to be able to implement custom behavior for the Android back button/gesture. This could possibly be done through a global event that can be listened for, but there should also be a way to disable the default behavior for it. There could also be a way to register a handler while initializing Tauri.

Alternatives considered

This could also be done by giving Tauri a way to manage the custom browser history, and telling the frontend or backend when the back/forward browser events are triggered. This could also be managed through the developer's frontend framework of choice, but it might require a refactor if the app framework isn't already using custom routing or separate browser pages.

Additional context

The Discord support thread that prompted this feature request

[niceEli]

this would be useful for my app to fully disable the back button

[Muhammed-Rahif]

src-tauri/gen/android/app/src/main/java/<your-thing>/MainActivity.kt:

package example.app.id

import android.webkit.WebView

class MainActivity : TauriActivity() {
  private lateinit var wv: WebView
  
  override fun onWebViewCreate(webView: WebView) {
    wv = webView
  }
  
  override fun onBackPressed() {
    wv.evaluateJavascript(/* script = */ """
      try {
        window.androidBackCallback()
      } catch (_) {
        true
      }
    """.trimIndent()) { result ->
      if (result == "true") {
        super.onBackPressed();
      }
    }
  }
}

On your front end javascript:

window.androidBackCallback = function () {
	// Something you have to do when back button pressed

	if(nothingToDo) return true; // which will do the default android back
	return false; // the android back will be prevented
}

---

Credits: @ahqsoftwares

[ahqsoftwares]

In the above example @Muhammed-Rahif you'll need to @SuppressDeprecation

[ahqsoftwares]

src-tauri/gen/android/app/src/main/java/<your-thing>/MainActivity.kt:

package example.app.id

import android.webkit.WebView
import android.annotation.SuppressLint


class MainActivity : TauriActivity() {
  private lateinit var wv: WebView
  
  override fun onWebViewCreate(webView: WebView) {
    wv = webView
  }
  
  @SuppressLint("MissingSuperCall", "SetTextI18n")
  @Deprecated("")
  override fun onBackPressed() {
    wv.evaluateJavascript(/* script = */ """
      try {
        window.androidBackCallback()
      } catch (_) {
        true
      }
    """.trimIndent()) { result ->
      if (result == "true") {
        super.onBackPressed();
      }
    }
  }
}

[Muhammed-Rahif]

Shouldn't we add import android.annotation.SuppressLint then?

[MattCozendey]

Any updates?

[ahqsoftwares]

Any updates?

Technically, we can do the thing, just need to use kotlin

[MilesVII]

The solution above mostly works, the app won't exit, but if I press anywhere on the screen and then press the back button, webview still performs navigation if I'm using some kind of web router. I assume that webview receives focus and then responds to buttons without passing the event to the activity. In my case, I had to also override dispatchKeyEvent

  import android.view.KeyEvent
  
  override fun dispatchKeyEvent(event: KeyEvent): Boolean {
    if (event.keyCode == KeyEvent.KEYCODE_BACK && event.action == KeyEvent.ACTION_DOWN) {
        if (wv.canGoBack()) {
            // optionally invoke window.androidBackCallback()
            return true
        }
    }
    return super.dispatchKeyEvent(event)
  }