Don't move to HotspotFragment on rotate when user navigated back to introduction

briar-android/src/main/java/org/briarproject/briar/android/hotspot/HotspotActivity.java

@@ -54,11 +54,14 @@ public class HotspotActivity extends BriarActivity
 		FragmentManager fm = getSupportFragmentManager();
 		viewModel.getState().observe(this, hotspotState -> {
 			if (hotspotState instanceof HotspotStarted) {
+				HotspotStarted started = (HotspotStarted) hotspotState;
 				String tag = HotspotFragment.TAG;
 				// check if fragment is already added
 				// to not lose state on configuration changes
 				if (fm.findFragmentByTag(tag) == null) {
-					showFragment(fm, new HotspotFragment(), tag);
+					if (!started.consume()) {
+						showFragment(fm, new HotspotFragment(), tag);
+					}
 				}
 			} else if (hotspotState instanceof HotspotError) {
 				HotspotError error = ((HotspotError) hotspotState);

briar-android/src/main/java/org/briarproject/briar/android/hotspot/HotspotState.java

@@ -5,6 +5,7 @@ import android.graphics.Bitmap;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import androidx.annotation.Nullable;
+import androidx.annotation.UiThread;
 
 @NotNullByDefault
 abstract class HotspotState {
@@ -38,6 +39,9 @@ abstract class HotspotState {
 	static class HotspotStarted extends HotspotState {
 		private final NetworkConfig networkConfig;
 		private final WebsiteConfig websiteConfig;
+		// 'consumed' is set to true once this state triggered a UI change, i.e.
+		// moving to the next fragment.
+		private boolean consumed = false;
 
 		HotspotStarted(NetworkConfig networkConfig,
 				WebsiteConfig websiteConfig) {
@@ -52,6 +56,18 @@ abstract class HotspotState {
 		WebsiteConfig getWebsiteConfig() {
 			return websiteConfig;
 		}
+
+		/**
+		 * Mark this state as consumed, i.e. the UI has already done something
+		 * as a result of the state changing to this. This can be used in order
+		 * to not repeat actions such as showing fragments on rotation changes.
+		 */
+		@UiThread
+		boolean consume() {
+			boolean old = consumed;
+			consumed = true;
+			return old;
+		}
 	}
 
 	static class HotspotError extends HotspotState {

briar-android/src/main/java/org/briarproject/briar/android/hotspot/HotspotViewModel.java

@@ -96,9 +96,13 @@ class HotspotViewModel extends DbViewModel
 	void startHotspot() {
 		HotspotState s = state.getValue();
 		if (s instanceof HotspotStarted) {
-			// Don't try to start again, if already started, just re-set value.
+			// This can happen if the user navigates back to intro fragment and
-			// This can happen if the user navigates back to intro fragment.
+			// taps 'start sharing' again. In this case, don't try to start the
-			state.setValue(s);
+			// hotspot again. Instead, just create a new, unconsumed HotspotStarted
+			// event with the same config.
+			HotspotStarted old = (HotspotStarted) s;
+			state.setValue(new HotspotStarted(old.getNetworkConfig(),
+					old.getWebsiteConfig()));
 		} else {
 			hotspotManager.startWifiP2pHotspot();
 			notificationManager.showHotspotNotification();