feat(core): back button event on Android, closes #8142

.changes/android-app-plugin.md

@@ -0,0 +1,5 @@
+---
+"tauri": minor:feat
+---
+
+Added mobile app plugin to support exit and back button press event.

.changes/back-button-press-api.md

@@ -0,0 +1,5 @@
+---
+"@tauri-apps/api": minor:feat
+---
+
+Added `app > onBackButtonPress` for Android back button handling.

crates/tauri-runtime-wry/Cargo.toml

@@ -17,7 +17,7 @@ rustc-args = ["--cfg", "docsrs"]
 rustdoc-args = ["--cfg", "docsrs"]
 
 [dependencies]
-wry = { version = "0.53.2", default-features = false, features = [
+wry = { version = "0.53.4", default-features = false, features = [
   "drag-drop",
   "protocol",
   "os-webview",

crates/tauri/build.rs

@@ -164,6 +164,8 @@ const PLUGINS: &[(&str, &[(&str, bool)])] = &[
       ("set_app_theme", false),
       ("set_dock_visibility", false),
       ("bundle_type", true),
+      ("register_listener", true),
+      ("remove_listener", true),
     ],
   ),
   (

crates/tauri/mobile/android-codegen/TauriActivity.kt

@@ -12,6 +12,7 @@ import app.tauri.plugin.PluginManager
 
 abstract class TauriActivity : WryActivity() {
   var pluginManager: PluginManager = PluginManager(this)
+  override val handleBackNavigation: Boolean = true
 
   override fun onNewIntent(intent: Intent) {
     super.onNewIntent(intent)

crates/tauri/mobile/android/src/main/java/app/tauri/AppPlugin.kt

@@ -0,0 +1,54 @@
+// Copyright 2019-2024 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+package app.tauri
+
+import android.app.Activity
+import android.webkit.WebView
+import androidx.activity.OnBackPressedCallback
+import androidx.appcompat.app.AppCompatActivity
+import app.tauri.annotation.Command
+import app.tauri.annotation.TauriPlugin
+import app.tauri.plugin.Plugin
+import app.tauri.plugin.Invoke
+import app.tauri.plugin.JSObject
+
+@TauriPlugin
+class AppPlugin(private val activity: Activity): Plugin(activity) {
+  private val BACK_BUTTON_EVENT = "back-button"
+
+  private var webView: WebView? = null
+
+  override fun load(webView: WebView) {
+    this.webView = webView
+  }
+
+  init {
+    val callback = object : OnBackPressedCallback(true) {
+      override fun handleOnBackPressed() {
+        if (!hasListener(BACK_BUTTON_EVENT)) {
+          if (this@AppPlugin.webView?.canGoBack() == true) {
+            this@AppPlugin.webView!!.goBack()
+          } else {
+            this.isEnabled = false
+            this@AppPlugin.activity.onBackPressed()
+            this.isEnabled = true
+          }
+        } else {
+          val data = JSObject().apply {
+            put("canGoBack", this@AppPlugin.webView?.canGoBack() ?: false)
+          }
+          trigger(BACK_BUTTON_EVENT, data)
+        }
+      }
+    }
+    (activity as AppCompatActivity).onBackPressedDispatcher.addCallback(activity, callback)
+  }
+
+  @Command
+  fun exit(invoke: Invoke) {
+    activity.finish()
+    invoke.resolve()
+  }
+}

crates/tauri/mobile/android/src/main/java/app/tauri/plugin/Plugin.kt

@@ -8,7 +8,6 @@ import android.app.Activity
 import android.content.Intent
 import android.content.pm.PackageManager
 import android.net.Uri
-import android.os.Bundle
 import android.webkit.WebView
 import androidx.activity.result.IntentSenderRequest
 import androidx.core.app.ActivityCompat
@@ -22,7 +21,6 @@ import app.tauri.annotation.InvokeArg
 import app.tauri.annotation.PermissionCallback
 import app.tauri.annotation.TauriPlugin
 import com.fasterxml.jackson.databind.ObjectMapper
-import org.json.JSONException
 import java.util.*
 import java.util.concurrent.CopyOnWriteArrayList
 
@@ -148,6 +146,10 @@ abstract class Plugin(private val activity: Activity) {
     }
   }
 
+  fun hasListener(event: String): Boolean {
+    return !listeners[event].isNullOrEmpty()
+  }
+
   @Command
   open fun registerListener(invoke: Invoke) {
     val args = invoke.parseArgs(RegisterListenerArgs::class.java)

crates/tauri/permissions/app/autogenerated/reference.md

@@ -9,6 +9,8 @@ Default permissions for the plugin.
 - `allow-tauri-version`
 - `allow-identifier`
 - `allow-bundle-type`
+- `allow-register-listener`
+- `allow-remove-listener`
 
 ## Permission Table
 
@@ -204,6 +206,32 @@ Denies the name command without any pre-configured scope.
 <tr>
 <td>
 
+`core:app:allow-register-listener`
+
+</td>
+<td>
+
+Enables the register_listener command without any pre-configured scope.
+
+</td>
+</tr>
+
+<tr>
+<td>
+
+`core:app:deny-register-listener`
+
+</td>
+<td>
+
+Denies the register_listener command without any pre-configured scope.
+
+</td>
+</tr>
+
+<tr>
+<td>
+
 `core:app:allow-remove-data-store`
 
 </td>
@@ -230,6 +258,32 @@ Denies the remove_data_store command without any pre-configured scope.
 <tr>
 <td>
 
+`core:app:allow-remove-listener`
+
+</td>
+<td>
+
+Enables the remove_listener command without any pre-configured scope.
+
+</td>
+</tr>
+
+<tr>
+<td>
+
+`core:app:deny-remove-listener`
+
+</td>
+<td>
+
+Denies the remove_listener command without any pre-configured scope.
+
+</td>
+</tr>
+
+<tr>
+<td>
+
 `core:app:allow-set-app-theme`
 
 </td>

crates/tauri/src/app/plugin.rs

@@ -132,5 +132,17 @@ pub fn init<R: Runtime>() -> TauriPlugin<R> {
       set_dock_visibility,
       bundle_type,
     ])
+    .setup(|_app, _api| {
+      #[cfg(target_os = "android")]
+      {
+        let handle = _api.register_android_plugin("app.tauri", "AppPlugin")?;
+        let handle_ref = &handle;
+        _app.manage(AppPlugin(*handle_ref));
+      }
+      Ok(())
+    })
     .build()
 }
+
+#[cfg(target_os = "android")]
+pub(crate) struct AppPlugin<R: Runtime>(pub crate::plugin::PluginHandle<R>);

crates/tauri/src/path/android.rs

@@ -4,10 +4,7 @@
 
 use super::Result;
 use crate::{plugin::PluginHandle, Runtime};
-use std::{
-  ffi::OsStr,
-  path::{Path, PathBuf},
-};
+use std::path::{Path, PathBuf};
 
 /// A helper class to access the mobile path APIs.
 pub struct PathResolver<R: Runtime>(pub(crate) PluginHandle<R>);

packages/api/src/app.ts

@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-License-Identifier: MIT
 
-import { invoke } from './core'
+import { addPluginListener, invoke, PluginListener } from './core'
 import { Image } from './image'
 import { Theme } from './window'
 
@@ -252,6 +252,28 @@ async function getBundleType(): Promise<BundleType> {
   return invoke('plugin:app|bundle_type')
 }
 
+/**
+ * Payload for the onBackButtonPress event.
+ */
+type OnBackButtonPressPayload = {
+  /** Whether the webview canGoBack property is true. */
+  canGoBack: boolean
+}
+
+/**
+ * Listens to the backButton event on Android.
+ * @param handler
+ */
+async function onBackButtonPress(
+  handler: (payload: OnBackButtonPressPayload) => void
+): Promise<PluginListener> {
+  return addPluginListener<OnBackButtonPressPayload>(
+    'app',
+    'back-button',
+    handler
+  )
+}
+
 export {
   getName,
   getVersion,
@@ -264,5 +286,7 @@ export {
   fetchDataStoreIdentifiers,
   removeDataStore,
   setDockVisibility,
-  getBundleType
+  getBundleType,
+  type OnBackButtonPressPayload,
+  onBackButtonPress
 }