fyne-io · andydotxyz · Aug 1, 2023 · Jun 5, 2023 · Jun 5, 2023 · Jul 28, 2023
diff --git a/cmd/fyne/internal/mobile/dex.go b/cmd/fyne/internal/mobile/dex.go
diff --git a/driver/mobile/driver.go b/driver/mobile/driver.go
@@ -0,0 +1,10 @@
+// Package mobile provides desktop specific mobile functionality.
+package mobile
+
+// Driver represents the extended capabilities of a mobile driver
+//
+// Since: 2.4
+type Driver interface {
+	// GoBack asks the OS to go to the previous app / activity, where supported
+	GoBack()
+}
diff --git a/driver/mobile/key.go b/driver/mobile/key.go
@@ -0,0 +1,10 @@
+package mobile
+
+import (
+	"fyne.io/fyne/v2"
+)
+
+const (
+	// KeyBack represents the back button which may be hardware or software
+	KeyBack fyne.KeyName = "Back"
+)
diff --git a/internal/driver/mobile/app/GoNativeActivity.java b/internal/driver/mobile/app/GoNativeActivity.java
@@ -43,6 +43,7 @@ public class GoNativeActivity extends NativeActivity {
     private native void insetsChanged(int top, int bottom, int left, int right);
     private native void keyboardTyped(String str);
     private native void keyboardDelete();
+    private native void backPressed();
     private native void setDarkMode(boolean dark);
 
 	private EditText mTextEdit;
@@ -313,6 +314,21 @@ protected void onActivityResult(int requestCode, int resultCode, Intent data) {
         filePickerReturned(uri.toString());
     }
 
+    @Override
+    public void onBackPressed() {
+        // skip the default behaviour - we can call finishActivity if we want to go back
+        backPressed();
+    }
+
+    public void finishActivity() {
+        runOnUiThread(new Runnable() {
+            @Override
+            public void run() {
+                GoNativeActivity.super.onBackPressed();
+            }
+        });
+    }
+
     @Override
     public void onConfigurationChanged(Configuration config) {
         super.onConfigurationChanged(config);

diff --git a/internal/driver/mobile/app/android.c b/internal/driver/mobile/app/android.c
@@ -53,6 +53,7 @@ static jmethodID show_keyboard_method;
 static jmethodID hide_keyboard_method;
 static jmethodID show_file_open_method;
 static jmethodID show_file_save_method;
+static jmethodID finish_method;
 
 jint JNI_OnLoad(JavaVM* vm, void* reserved) {
 	JNIEnv* env;
@@ -65,6 +66,14 @@ jint JNI_OnLoad(JavaVM* vm, void* reserved) {
 
 static int main_running = 0;
 
+// ensure we refresh context on resume in case something has changed...
+void processOnResume(ANativeActivity *activity) {
+	JNIEnv* env = activity->env;
+	setCurrentContext(activity->vm, (*env)->NewGlobalRef(env, activity->clazz));
+
+    onResume(activity);
+}
+
 // Entry point from our subclassed NativeActivity.
 //
 // By here, the Go runtime has been initialized (as we are running in
@@ -85,6 +94,7 @@ void ANativeActivity_onCreate(ANativeActivity *activity, void* savedState, size_
 		hide_keyboard_method = find_static_method(env, current_class, "hideKeyboard", "()V");
 		show_file_open_method = find_static_method(env, current_class, "showFileOpen", "(Ljava/lang/String;)V");
 		show_file_save_method = find_static_method(env, current_class, "showFileSave", "(Ljava/lang/String;Ljava/lang/String;)V");
+		finish_method = find_method(env, current_class, "finishActivity", "()V");
 
 		setCurrentContext(activity->vm, (*env)->NewGlobalRef(env, activity->clazz));
 
@@ -117,7 +127,7 @@ void ANativeActivity_onCreate(ANativeActivity *activity, void* savedState, size_
 	// Note that onNativeWindowResized is not called on resize. Avoid it.
 	// https://code.google.com/p/android/issues/detail?id=180645
 	activity->callbacks->onStart = onStart;
-	activity->callbacks->onResume = onResume;
+	activity->callbacks->onResume = processOnResume;
 	activity->callbacks->onSaveInstanceState = onSaveInstanceState;
 	activity->callbacks->onPause = onPause;
 	activity->callbacks->onStop = onStop;
@@ -204,6 +214,13 @@ char* destroyEGLSurface() {
 	return NULL;
 }
 
+void finish(JNIEnv* env, jobject ctx) {
+    (*env)->CallVoidMethod(
+        env,
+        ctx,
+        finish_method);
+}
+
 int32_t getKeyRune(JNIEnv* env, AInputEvent* e) {
 	return (int32_t)(*env)->CallStaticIntMethod(
 		env,
@@ -272,6 +289,10 @@ void Java_org_golang_app_GoNativeActivity_keyboardDelete(JNIEnv *env, jclass cla
     keyboardDelete();
 }
 
+void Java_org_golang_app_GoNativeActivity_backPressed(JNIEnv *env, jclass clazz) {
+    onBackPressed();
+}
+
 void Java_org_golang_app_GoNativeActivity_setDarkMode(JNIEnv *env, jclass clazz, jboolean dark) {
     setDarkMode((bool)dark);
 }
diff --git a/internal/driver/mobile/app/android.go b/internal/driver/mobile/app/android.go
@@ -48,6 +48,7 @@ void showKeyboard(JNIEnv* env, int keyboardType);
 void hideKeyboard(JNIEnv* env);
 void showFileOpen(JNIEnv* env, char* mimes);
 void showFileSave(JNIEnv* env, char* mimes, char* filename);
+void finish(JNIEnv* env, jobject ctx);
 
 void Java_org_golang_app_GoNativeActivity_filePickerReturned(JNIEnv *env, jclass clazz, jstring str);
 */
@@ -77,6 +78,18 @@ var mimeMap = map[string]string{
 	".txt": "text/plain",
 }
 
+// GoBack asks the OS to go to the previous app / activity
+func GoBack() {
+	err := RunOnJVM(func(_, jniEnv, ctx uintptr) error {
+		env := (*C.JNIEnv)(unsafe.Pointer(jniEnv))
+		C.finish(env, C.jobject(ctx))
+		return nil
+	})
+	if err != nil {
+		log.Fatalf("app: %v", err)
+	}
+}
+
 // RunOnJVM runs fn on a new goroutine locked to an OS thread with a JNIEnv.
 //
 // RunOnJVM blocks until the call to fn is complete. Any Java
@@ -139,6 +152,19 @@ func onPause(activity *C.ANativeActivity) {
 func onStop(activity *C.ANativeActivity) {
 }
 
+//export onBackPressed
+func onBackPressed() {
+	k := key.Event{
+		Code:      key.CodeBackButton,
+		Direction: key.DirPress,
+	}
+	log.Println("Logging key event back")
+	theApp.events.In() <- k
+
+	k.Direction = key.DirRelease
+	theApp.events.In() <- k
+}
+
 //export onCreate
 func onCreate(activity *C.ANativeActivity) {
 	// Set the initial configuration.

diff --git a/internal/driver/mobile/app/darwin_desktop.go b/internal/driver/mobile/app/darwin_desktop.go
@@ -63,6 +63,10 @@ func main(f func(App)) {
 	C.runApp()
 }
 
+func GoBack() {
+	// When simulating mobile there are no other activities open (and we can't just force background)
+}
+
 // loop is the primary drawing loop.
 //
 // After Cocoa has captured the initial OS thread for processing Cocoa

diff --git a/internal/driver/mobile/app/darwin_ios.go b/internal/driver/mobile/app/darwin_ios.go
@@ -82,6 +82,10 @@ var DisplayMetrics struct {
 	HeightPx int
 }
 
+func GoBack() {
+	// Apple do not permit apps to exit in any way other than user pressing home button / gesture
+}
+
 //export setDisplayMetrics
 func setDisplayMetrics(width, height int, scale int) {
 	DisplayMetrics.WidthPx = width

diff --git a/internal/driver/mobile/app/shiny.go b/internal/driver/mobile/app/shiny.go
@@ -15,6 +15,10 @@ func main(f func(a App)) {
 	fmt.Errorf("Running mobile simulation mode does not currently work on Windows.")
 }
 
+func GoBack() {
+	// When simulating mobile there are no other activities open (and we can't just force background)
+}
+
 // driverShowVirtualKeyboard does nothing on desktop
 func driverShowVirtualKeyboard(KeyboardType) {
 }

diff --git a/internal/driver/mobile/app/x11.go b/internal/driver/mobile/app/x11.go
@@ -80,6 +80,10 @@ func main(f func(App)) {
 	}
 }
 
+func GoBack() {
+	// When simulating mobile there are no other activities open (and we can't just force background)
+}
+
 //export onResize
 func onResize(w, h int) {
 	// TODO(nigeltao): don't assume 72 DPI. DisplayWidth and DisplayWidthMM

diff --git a/internal/driver/mobile/driver.go b/internal/driver/mobile/driver.go
@@ -7,6 +7,7 @@ import (
 
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/canvas"
+	"fyne.io/fyne/v2/driver/mobile"
 	"fyne.io/fyne/v2/internal"
 	"fyne.io/fyne/v2/internal/animation"
 	intapp "fyne.io/fyne/v2/internal/app"
@@ -127,6 +128,10 @@ func (d *mobileDriver) AbsolutePositionForObject(co fyne.CanvasObject) fyne.Posi
 	return pos.Subtract(inset)
 }
 
+func (d *mobileDriver) GoBack() {
+	app.GoBack()
+}
+
 func (d *mobileDriver) Quit() {
 	// Android and iOS guidelines say this should not be allowed!
 }
@@ -458,6 +463,8 @@ var keyCodeMap = map[key.Code]fyne.KeyName{
 	key.CodeBackslash:          fyne.KeyBackslash,
 	key.CodeRightSquareBracket: fyne.KeyRightBracket,
 	key.CodeGraveAccent:        fyne.KeyBackTick,
+
+	key.CodeBackButton: mobile.KeyBack,
 }
 
 func keyToName(code key.Code) fyne.KeyName {
@@ -508,8 +515,12 @@ func (d *mobileDriver) typeDownCanvas(canvas *mobileCanvas, r rune, code key.Cod
 			canvas.Focused().TypedRune(r)
 		}
 	} else {
-		if keyName != "" && canvas.onTypedKey != nil {
-			canvas.onTypedKey(keyEvent)
+		if keyName != "" {
+			if canvas.onTypedKey != nil {
+				canvas.onTypedKey(keyEvent)
+			} else if keyName == mobile.KeyBack {
+				d.GoBack()
+			}
 		}
 		if r > 0 && canvas.onTypedRune != nil {
 			canvas.onTypedRune(r)

diff --git a/internal/driver/mobile/event/key/key.go b/internal/driver/mobile/event/key/key.go
@@ -221,6 +221,8 @@ const (
 	CodeRightAlt     Code = 230
 	CodeRightGUI     Code = 231
 
+	CodeBackButton Code = 301 // anything above 255 is not used in the USB spec
+
 	// The following codes are not part of the standard USB HID Usage IDs for
 	// keyboards. See http://www.usb.org/developers/hidpage/Hut1_12v2.pdf
 	//