[android] address review comments for image fullscreen swiping

briar-android/src/main/java/org/briarproject/briar/android/conversation/ImageActivity.java

@@ -134,7 +134,7 @@ public class ImageActivity extends BriarActivity
 		viewPager.setCurrentItem(position);
 
 		if (SDK_INT >= 16) {
-			viewModel.getOnImageClicked().observe(this, this::onPhotoClicked);
+			viewModel.getOnImageClicked().observe(this, this::onImageClicked);
 			window.getDecorView().setSystemUiVisibility(
 					SYSTEM_UI_FLAG_LAYOUT_STABLE |
 							SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
@@ -168,6 +168,8 @@ public class ImageActivity extends BriarActivity
 		);
 		if (SDK_INT >= 16) {
 			layout.getViewTreeObserver().removeOnGlobalLayoutListener(this);
+		} else {
+			layout.getViewTreeObserver().removeGlobalOnLayoutListener(this);
 		}
 	}
 
@@ -203,8 +205,9 @@ public class ImageActivity extends BriarActivity
 		supportFinishAfterTransition();
 	}
 
-	private void onPhotoClicked(@Nullable Boolean clicked) {
-		if (clicked != null&& clicked && SDK_INT >= 16) {
+	@RequiresApi(api = 16)
+	private void onImageClicked(@Nullable Boolean clicked) {
+		if (clicked != null && clicked) {
 			toggleSystemUi();
 			viewModel.onOnImageClickSeen();
 		}

briar-android/src/main/java/org/briarproject/briar/android/conversation/ImageFragment.java

@@ -77,7 +77,7 @@ public class ImageFragment extends Fragment {
 				viewModelFactory).get(ImageViewModel.class);
 
 		photoView = v.findViewById(R.id.photoView);
-		photoView.setOnClickListener(view -> viewModel.clickPhoto());
+		photoView.setOnClickListener(view -> viewModel.clickImage());
 
 		// Request Listener
 		RequestListener<Drawable> listener = new RequestListener<Drawable>() {

briar-android/src/main/java/org/briarproject/briar/android/conversation/ImageViewModel.java

@@ -50,7 +50,8 @@ public class ImageViewModel extends AndroidViewModel {
 	@IoExecutor
 	private final Executor ioExecutor;
 
-	private final MutableLiveData<Boolean> imageClicked = new MutableLiveData<>();
+	private final MutableLiveData<Boolean> imageClicked =
+			new MutableLiveData<>();
 	private final MutableLiveData<Boolean> saveState = new MutableLiveData<>();
 	private int toolbarTop, toolbarBottom;
 
@@ -65,7 +66,7 @@ public class ImageViewModel extends AndroidViewModel {
 		this.ioExecutor = ioExecutor;
 	}
 
-	void clickPhoto() {
+	void clickImage() {
 		imageClicked.setValue(true);
 	}
 
@@ -97,7 +98,7 @@ public class ImageViewModel extends AndroidViewModel {
 		float scaleFactor = Math.min(widthPercentage, heightPercentage);
 		int realWidth = (int) (width * scaleFactor);
 		int realHeight = (int) (height * scaleFactor);
-		// return if photo doesn't use the full width,
+		// return if image doesn't use the full width,
 		// because it will be moved to the right otherwise
 		if (realWidth < screenView.getWidth()) return false;
 		int drawableTop = (screenView.getHeight() - realHeight) / 2;