Transfer Data UI

briar-android/src/main/java/org/briarproject/briar/android/AndroidComponent.java

@@ -38,6 +38,9 @@ import org.briarproject.briar.android.attachment.media.MediaModule;
 import org.briarproject.briar.android.conversation.glide.BriarModelLoader;
 import org.briarproject.briar.android.logging.CachingLogHandler;
 import org.briarproject.briar.android.login.SignInReminderReceiver;
+import org.briarproject.briar.android.removabledrive.ChooserFragment;
+import org.briarproject.briar.android.removabledrive.ReceiveFragment;
+import org.briarproject.briar.android.removabledrive.SendFragment;
 import org.briarproject.briar.android.settings.ConnectionsFragment;
 import org.briarproject.briar.android.settings.NotificationsFragment;
 import org.briarproject.briar.android.settings.SecurityFragment;
@@ -212,4 +215,10 @@ public interface AndroidComponent
 	void inject(SecurityFragment securityFragment);
 
 	void inject(NotificationsFragment notificationsFragment);
+
+	void inject(ChooserFragment chooserFragment);
+
+	void inject(SendFragment sendFragment);
+
+	void inject(ReceiveFragment receiveFragment);
 }

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -25,7 +25,6 @@ import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.reporting.DevConfig;
 import org.briarproject.bramble.plugin.bluetooth.AndroidBluetoothPluginFactory;
 import org.briarproject.bramble.plugin.file.AndroidRemovableDrivePluginFactory;
-import org.briarproject.bramble.plugin.file.RemovableDriveModule;
 import org.briarproject.bramble.plugin.tcp.AndroidLanTcpPluginFactory;
 import org.briarproject.bramble.plugin.tor.AndroidTorPluginFactory;
 import org.briarproject.bramble.util.AndroidUtils;
@@ -43,6 +42,7 @@ import org.briarproject.briar.android.login.LoginModule;
 import org.briarproject.briar.android.navdrawer.NavDrawerModule;
 import org.briarproject.briar.android.privategroup.conversation.GroupConversationModule;
 import org.briarproject.briar.android.privategroup.list.GroupListModule;
+import org.briarproject.briar.android.removabledrive.TransferDataModule;
 import org.briarproject.briar.android.reporting.DevReportModule;
 import org.briarproject.briar.android.settings.SettingsModule;
 import org.briarproject.briar.android.sharing.SharingModule;
@@ -93,7 +93,7 @@ import static org.briarproject.briar.android.TestingConstants.IS_DEBUG_BUILD;
 		GroupListModule.class,
 		GroupConversationModule.class,
 		SharingModule.class,
-		RemovableDriveModule.class
+		TransferDataModule.class,
 })
 public class AppModule {
 

briar-android/src/main/java/org/briarproject/briar/android/activity/RequestCodes.java

@@ -14,7 +14,5 @@ public interface RequestCodes {
 	int REQUEST_ATTACH_IMAGE = 13;
 	int REQUEST_SAVE_ATTACHMENT = 14;
 	int REQUEST_AVATAR_IMAGE = 15;
-	int REQUEST_REMOVABLE_DRIVE_WRITE = 16;
-	int REQUEST_REMOVABLE_DRIVE_READ = 17;
 
 }

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

@@ -375,6 +375,10 @@ public class ConversationActivity extends BriarActivity
 		if (!featureFlags.shouldEnableConnectViaBluetooth()) {
 			menu.findItem(R.id.action_connect_via_bluetooth).setVisible(false);
 		}
+		// Transfer Data feature only supported on API 19+
+		if (SDK_INT >= 19) { // TODO also hide behind feature flag
+			menu.findItem(R.id.action_transfer_data).setVisible(true);
+		}
 		// enable alias and bluetooth action once available
 		observeOnce(viewModel.getContactItem(), this, contact -> {
 			menu.findItem(R.id.action_set_alias).setEnabled(true);
@@ -415,17 +419,17 @@ public class ConversationActivity extends BriarActivity
 			new BluetoothConnecterDialogFragment().show(fm,
 					BluetoothConnecterDialogFragment.TAG);
 			return true;
+		} else if (itemId == R.id.action_transfer_data) {
+			Intent intent = new Intent(this, RemovableDriveActivity.class);
+			intent.putExtra(CONTACT_ID, contactId.getInt());
+			startActivity(intent);
+			return true;
 		} else if (itemId == R.id.action_delete_all_messages) {
 			askToDeleteAllMessages();
 			return true;
 		} else if (itemId == R.id.action_social_remove_person) {
 			askToRemoveContact();
 			return true;
-		} else if (itemId == R.id.action_removable_drive_write) {
-			Intent intent = new Intent(this, RemovableDriveActivity.class);
-			intent.putExtra(CONTACT_ID, contactId.getInt());
-			startActivity(intent);
-			return true;
 		}
 		return super.onOptionsItemSelected(item);
 	}

briar-android/src/main/java/org/briarproject/briar/android/fragment/FinalFragment.java

@@ -0,0 +1,108 @@
+package org.briarproject.briar.android.fragment;
+
+import android.content.res.ColorStateList;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+import android.widget.ImageView;
+import android.widget.TextView;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+
+import androidx.activity.OnBackPressedCallback;
+import androidx.annotation.ColorRes;
+import androidx.annotation.DrawableRes;
+import androidx.annotation.Nullable;
+import androidx.annotation.StringRes;
+import androidx.appcompat.app.ActionBar;
+import androidx.appcompat.app.AppCompatActivity;
+import androidx.core.widget.ImageViewCompat;
+import androidx.fragment.app.Fragment;
+
+/**
+ * A fragment to be used at the end of a user flow
+ * where the user should not have the option to go back.
+ * Here, we only show final information
+ * before finishing the related activity.
+ */
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class FinalFragment extends Fragment {
+
+	public static final String TAG = FinalFragment.class.getName();
+
+	public static final String ARG_TITLE = "title";
+	public static final String ARG_ICON = "icon";
+	public static final String ARG_ICON_TINT = "iconTint";
+	public static final String ARG_TEXT = "text";
+
+	public static FinalFragment newInstance(
+			@StringRes int title,
+			@DrawableRes int icon,
+			@ColorRes int iconTint,
+			@StringRes int text) {
+		FinalFragment f = new FinalFragment();
+		Bundle args = new Bundle();
+		args.putInt(ARG_TITLE, title);
+		args.putInt(ARG_ICON, icon);
+		args.putInt(ARG_ICON_TINT, iconTint);
+		args.putInt(ARG_TEXT, text);
+		f.setArguments(args);
+		return f;
+	}
+
+	protected Button buttonView;
+
+	@Nullable
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View v = inflater
+				.inflate(R.layout.fragment_final, container, false);
+
+		ImageView iconView = v.findViewById(R.id.iconView);
+		TextView titleView = v.findViewById(R.id.titleView);
+		TextView textView = v.findViewById(R.id.textView);
+		buttonView = v.findViewById(R.id.button);
+
+		Bundle args = requireArguments();
+		titleView.setText(args.getInt(ARG_TITLE));
+		iconView.setImageResource(args.getInt(ARG_ICON));
+		int color = getResources().getColor(args.getInt(ARG_ICON_TINT));
+		ColorStateList tint = ColorStateList.valueOf(color);
+		ImageViewCompat.setImageTintList(iconView, tint);
+		textView.setText(args.getInt(ARG_TEXT));
+
+		buttonView.setOnClickListener(view -> onBackButtonPressed());
+
+		AppCompatActivity a = (AppCompatActivity) requireActivity();
+		a.setTitle(args.getInt(ARG_TITLE));
+		ActionBar actionBar = a.getSupportActionBar();
+		if (actionBar != null) {
+			actionBar.setDisplayHomeAsUpEnabled(false);
+			actionBar.setHomeButtonEnabled(false);
+		}
+		a.getOnBackPressedDispatcher().addCallback(
+				getViewLifecycleOwner(), new OnBackPressedCallback(true) {
+					@Override
+					public void handleOnBackPressed() {
+						onBackButtonPressed();
+					}
+				});
+		return v;
+	}
+
+	/**
+	 * This is the action that the system back button
+	 * and the button at the bottom will perform.
+	 */
+	protected void onBackButtonPressed() {
+		requireActivity().supportFinishAfterTransition();
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/removabledrive/ChooserFragment.java

@@ -0,0 +1,70 @@
+package org.briarproject.briar.android.removabledrive;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+import androidx.fragment.app.FragmentActivity;
+import androidx.lifecycle.ViewModelProvider;
+
+import static org.briarproject.briar.android.AppModule.getAndroidComponent;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class ChooserFragment extends Fragment {
+
+	public final static String TAG = ChooserFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private RemovableDriveViewModel viewModel;
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		FragmentActivity activity = requireActivity();
+		getAndroidComponent(activity).inject(this);
+		viewModel = new ViewModelProvider(activity, viewModelFactory)
+				.get(RemovableDriveViewModel.class);
+	}
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View v = inflater.inflate(R.layout.fragment_transfer_data_chooser,
+				container, false);
+
+		Button sendButton = v.findViewById(R.id.sendButton);
+		sendButton.setOnClickListener(i -> viewModel.startSendData());
+
+		Button receiveButton = v.findViewById(R.id.receiveButton);
+		receiveButton.setOnClickListener(i -> viewModel.startReceiveData());
+
+		return v;
+	}
+
+	@Override
+	public void onStart() {
+		super.onStart();
+		requireActivity().setTitle(R.string.removable_drive_menu_title);
+		if (viewModel.getState().getValue() != null) {
+			// we can't come back here now to start another action
+			// as we only support one per ViewModel instance
+			requireActivity().supportFinishAfterTransition();
+		}
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/removabledrive/ErrorFragment.java

@@ -0,0 +1,54 @@
+package org.briarproject.briar.android.removabledrive;
+
+import android.content.Intent;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.fragment.FinalFragment;
+
+import androidx.annotation.Nullable;
+import androidx.annotation.StringRes;
+
+import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class ErrorFragment extends FinalFragment {
+
+	public static ErrorFragment newInstance(@StringRes int title,
+			@StringRes int text) {
+		ErrorFragment f = new ErrorFragment();
+		Bundle args = new Bundle();
+		args.putInt(ARG_TITLE, title);
+		args.putInt(ARG_ICON, R.drawable.alerts_and_states_error);
+		args.putInt(ARG_ICON_TINT, R.color.briar_red_500);
+		args.putInt(ARG_TEXT, text);
+		f.setArguments(args);
+		return f;
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View v = super.onCreateView(inflater, container, savedInstanceState);
+		buttonView.setText(R.string.try_again_button);
+		return v;
+	}
+
+	@Override
+	protected void onBackButtonPressed() {
+		// Re-create this activity when going back in failed state.
+		// This will also re-create the ViewModel, so we start fresh.
+		Intent i = requireActivity().getIntent();
+		i.setFlags(FLAG_ACTIVITY_CLEAR_TOP);
+		startActivity(i);
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/removabledrive/ReceiveFragment.java

@@ -0,0 +1,106 @@
+package org.briarproject.briar.android.removabledrive;
+
+import android.content.Context;
+import android.net.Uri;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+import android.widget.ProgressBar;
+import android.widget.TextView;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+
+import javax.inject.Inject;
+
+import androidx.activity.result.ActivityResultLauncher;
+import androidx.activity.result.contract.ActivityResultContracts.GetContent;
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+import androidx.fragment.app.FragmentActivity;
+import androidx.lifecycle.ViewModelProvider;
+
+import static android.view.View.VISIBLE;
+import static android.widget.Toast.LENGTH_LONG;
+import static org.briarproject.briar.android.AppModule.getAndroidComponent;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class ReceiveFragment extends Fragment {
+
+	final static String TAG = ReceiveFragment.class.getName();
+
+	// TODO we can pass an extra named DocumentsContract.EXTRA_INITIAL_URI
+	//  to have the file-picker start on the usb-stick -- if get hold of URI
+	//  of the same. USB manager API?
+	//  Overall, passing this extra requires extending the ready-made
+	//  contracts and overriding createIntent.
+	private final ActivityResultLauncher<String> launcher =
+			registerForActivityResult(new GetContent(), this::onDocumentChosen);
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	RemovableDriveViewModel viewModel;
+	TextView introTextView;
+	Button button;
+	ProgressBar progressBar;
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		FragmentActivity activity = requireActivity();
+		getAndroidComponent(activity).inject(this);
+		viewModel = new ViewModelProvider(activity, viewModelFactory)
+				.get(RemovableDriveViewModel.class);
+	}
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View v = inflater.inflate(R.layout.fragment_transfer_data_receive,
+				container, false);
+
+		introTextView = v.findViewById(R.id.introTextView);
+		progressBar = v.findViewById(R.id.progressBar);
+		button = v.findViewById(R.id.fileButton);
+		button.setOnClickListener(view ->
+				launcher.launch("*/*")
+		);
+		viewModel.getState()
+				.observe(getViewLifecycleOwner(), this::onStateChanged);
+		return v;
+	}
+
+	@Override
+	public void onStart() {
+		super.onStart();
+		requireActivity().setTitle(R.string.removable_drive_title_receive);
+	}
+
+	private void onStateChanged(TransferDataState state) {
+		if (state instanceof TransferDataState.NoDataToSend) {
+			throw new IllegalStateException();
+		} else if (state instanceof TransferDataState.Ready) {
+			button.setVisibility(VISIBLE);
+		} else if (state instanceof TransferDataState.TaskAvailable) {
+			button.setEnabled(false);
+			if (((TransferDataState.TaskAvailable) state).isOldTask) {
+				Toast.makeText(requireContext(),
+						R.string.removable_drive_ongoing, LENGTH_LONG).show();
+			}
+			progressBar.setVisibility(VISIBLE);
+		}
+	}
+
+	private void onDocumentChosen(@Nullable Uri uri) {
+		if (uri == null) return;
+		viewModel.importData(uri);
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/removabledrive/RemovableDriveActivity.java

@@ -1,51 +1,42 @@
 package org.briarproject.briar.android.removabledrive;
 
 import android.content.Intent;
-import android.net.Uri;
 import android.os.Bundle;
 import android.view.MenuItem;
-import android.widget.Button;
-import android.widget.TextView;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.api.plugin.file.RemovableDriveTask.State;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BriarActivity;
-import org.briarproject.briar.android.fragment.BaseFragment.BaseFragmentListener;
-
-import java.text.SimpleDateFormat;
-import java.util.Date;
-import java.util.Locale;
+import org.briarproject.briar.android.fragment.FinalFragment;
+import org.briarproject.briar.android.removabledrive.RemovableDriveViewModel.Action;
+import org.briarproject.briar.android.removabledrive.TransferDataState.TaskAvailable;
 
 import javax.inject.Inject;
 
-import androidx.activity.result.ActivityResultLauncher;
-import androidx.activity.result.contract.ActivityResultContracts;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
-import androidx.lifecycle.LiveData;
+import androidx.annotation.StringRes;
+import androidx.fragment.app.Fragment;
 import androidx.lifecycle.ViewModelProvider;
 
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.briar.android.conversation.ConversationActivity.CONTACT_ID;
+import static org.briarproject.briar.android.util.UiUtils.showFragment;
 
-// TODO 19 will be our requirement for sneakernet support, right. The file apis
-//  used require this.
-@RequiresApi(api = 19)
+@RequiresApi(19)
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
-public class RemovableDriveActivity extends BriarActivity
-		implements BaseFragmentListener {
+public class RemovableDriveActivity extends BriarActivity {
 
 	@Inject
 	ViewModelProvider.Factory viewModelFactory;
+
 	private RemovableDriveViewModel viewModel;
-	private TextView text;
-	private Button writeButton;
-	private Button readButton;
 
 	@Override
 	public void injectActivity(ActivityComponent component) {
@@ -58,57 +49,23 @@ public class RemovableDriveActivity extends BriarActivity
 	@Override
 	public void onCreate(@Nullable Bundle savedInstanceState) {
 		super.onCreate(savedInstanceState);
-		setContentView(R.layout.activity_removable_drive);
-		text = findViewById(R.id.sneaker_text);
-		writeButton = findViewById(R.id.sneaker_write);
-		readButton = findViewById(R.id.sneaker_read);
 
-		Intent intent = getIntent();
+		Intent intent = requireNonNull(getIntent());
 		int contactId = intent.getIntExtra(CONTACT_ID, -1);
-		if (contactId == -1) {
-			writeButton.setEnabled(false);
-			readButton.setEnabled(false);
-			return;
-		}
+		if (contactId == -1) throw new IllegalArgumentException("ContactId");
+		viewModel.setContactId(new ContactId(contactId));
 
-		// TODO we can pass an extra named DocumentsContract.EXTRA_INITIAL_URI
-		//  to have the filepicker start on the usb-stick -- if get hold of URI
-		//  of the same. USB manager API?
-		//  Overall, passing this extra requires extending the ready-made
-		//  contracts and overriding createIntent.
+		setContentView(R.layout.activity_fragment_container);
 
-		writeButton.setText("Write for contactId " + contactId);
-		ActivityResultLauncher<String> createDocument =
-				registerForActivityResult(
-						new ActivityResultContracts.CreateDocument(),
-						uri -> write(contactId, uri));
-		writeButton.setOnClickListener(
-				v -> createDocument.launch(viewModel.getFileName()));
+		viewModel.getActionEvent().observeEvent(this, this::onActionReceived);
+		viewModel.getState().observe(this, this::onStateChanged);
 
-		readButton.setText("Read for contactId " + contactId);
-		ActivityResultLauncher<String> getContent =
-				registerForActivityResult(
-						new ActivityResultContracts.GetContent(),
-						uri -> read(contactId, uri));
-		readButton.setOnClickListener(
-				v -> getContent.launch("application/octet-stream"));
-
-		LiveData<State> state;
-		state = viewModel.ongoingWrite(new ContactId(contactId));
-		if (state == null) {
-			writeButton.setEnabled(true);
-		} else {
-			say("\nOngoing write:");
-			writeButton.setEnabled(false);
-			state.observe(this, (taskState) -> handleState("write", taskState));
-		}
-		state = viewModel.ongoingRead(new ContactId(contactId));
-		if (state == null) {
-			readButton.setEnabled(true);
-		} else {
-			say("\nOngoing read:");
-			readButton.setEnabled(false);
-			state.observe(this, (taskState) -> handleState("read", taskState));
+		if (savedInstanceState == null) {
+			Fragment f = new ChooserFragment();
+			String tag = ChooserFragment.TAG;
+			getSupportFragmentManager().beginTransaction()
+					.replace(R.id.fragmentContainer, f, tag)
+					.commit();
 		}
 	}
 
@@ -121,54 +78,56 @@ public class RemovableDriveActivity extends BriarActivity
 		return super.onOptionsItemSelected(item);
 	}
 
-	private void write(int contactId, @Nullable Uri uri) {
-		if (contactId == -1) {
-			throw new IllegalStateException();
-		}
-		if (uri == null) {
-			say("no URI picked for write");
-			return;
-		}
-		say("\nWriting to URI: " + uri);
-		writeButton.setEnabled(false);
-		LiveData<State> state = viewModel.write(new ContactId(contactId), uri);
-		state.observe(this, (taskState) -> handleState("write", taskState));
+	private void onActionReceived(Action action) {
+		Fragment f;
+		String tag;
+		if (action == Action.SEND) {
+			f = new SendFragment();
+			tag = SendFragment.TAG;
+		} else if (action == Action.RECEIVE) {
+			f = new ReceiveFragment();
+			tag = ReceiveFragment.TAG;
+		} else throw new AssertionError();
+		showFragment(getSupportFragmentManager(), f, tag);
 	}
 
-	private void read(int contactId, @Nullable Uri uri) {
-		if (contactId == -1) {
-			throw new IllegalStateException();
-		}
-		if (uri == null) {
-			say("no URI picked for read");
-			return;
-		}
-		say("\nReading from URI: " + uri);
-		readButton.setEnabled(false);
-		LiveData<State> state = viewModel.read(new ContactId(contactId), uri);
-		state.observe(this, (taskState) -> handleState("read", taskState));
-	}
-
-	private void handleState(String action, State taskState) {
-		say(String.format(Locale.getDefault(),
-				"%s: bytes done: %d of %d. %s. %s.",
-				action, taskState.getDone(), taskState.getTotal(),
-				taskState.isFinished() ? "Finished" : "Ongoing",
-				taskState.isFinished() ?
-						(taskState.isSuccess() ? "Success" : "Failed") : ".."));
-		if (taskState.isFinished()) {
-			if (action.equals("write")) {
-				writeButton.setEnabled(true);
-			} else if (action.equals("read")) {
-				readButton.setEnabled(true);
-			}
+	private void onStateChanged(TransferDataState state) {
+		if (!(state instanceof TaskAvailable)) return;
+		RemovableDriveTask.State s = ((TaskAvailable) state).state;
+		if (s.isFinished()) {
+			Action action =
+					requireNonNull(viewModel.getActionEvent().getLastValue());
+			Fragment f;
+			if (s.isSuccess()) f = getSuccessFragment(action);
+			else f = getErrorFragment(action);
+			showFragment(getSupportFragmentManager(), f, FinalFragment.TAG);
 		}
 	}
 
-	private void say(String txt) {
-		String time = new SimpleDateFormat("HH:mm:ss", Locale.getDefault())
-				.format(new Date());
-		txt = String.format("%s %s\n", time, txt);
-		text.setText(text.getText().toString().concat(txt));
+	private Fragment getSuccessFragment(Action action) {
+		@StringRes int title, text;
+		if (action == Action.SEND) {
+			title = R.string.removable_drive_success_send_title;
+			text = R.string.removable_drive_success_send_text;
+		} else if (action == Action.RECEIVE) {
+			title = R.string.removable_drive_success_receive_title;
+			text = R.string.removable_drive_success_receive_text;
+		} else throw new AssertionError();
+		return FinalFragment.newInstance(title,
+				R.drawable.ic_check_circle_outline, R.color.briar_brand_green,
+				text);
 	}
+
+	private Fragment getErrorFragment(Action action) {
+		@StringRes int title, text;
+		if (action == Action.SEND) {
+			title = R.string.removable_drive_error_send_title;
+			text = R.string.removable_drive_error_send_text;
+		} else if (action == Action.RECEIVE) {
+			title = R.string.removable_drive_error_receive_title;
+			text = R.string.removable_drive_error_receive_text;
+		} else throw new AssertionError();
+		return ErrorFragment.newInstance(title, text);
+	}
+
 }

briar-android/src/main/java/org/briarproject/briar/android/removabledrive/RemovableDriveViewModel.java

@@ -10,92 +10,159 @@ import org.briarproject.bramble.api.plugin.file.RemovableDriveManager;
 import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
 import org.briarproject.bramble.api.plugin.file.RemovableDriveTask.State;
 import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.briar.android.viewmodel.LiveEvent;
+import org.briarproject.briar.android.viewmodel.MutableLiveEvent;
 
 import java.text.SimpleDateFormat;
 import java.util.Date;
-import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
+import androidx.annotation.UiThread;
 import androidx.lifecycle.AndroidViewModel;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.MutableLiveData;
 
 import static java.util.Locale.US;
+import static java.util.Objects.requireNonNull;
 import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.PROP_URI;
 
+@UiThread
 @NotNullByDefault
 class RemovableDriveViewModel extends AndroidViewModel {
 
 	private static final Logger LOG =
 			getLogger(RemovableDriveViewModel.class.getName());
 
+	enum Action {SEND, RECEIVE}
+
 	private final RemovableDriveManager manager;
 
-	private final ConcurrentHashMap<Consumer<State>, RemovableDriveTask>
-			observers = new ConcurrentHashMap<>();
+	private final MutableLiveEvent<Action> action = new MutableLiveEvent<>();
+	private final MutableLiveData<TransferDataState> state =
+			new MutableLiveData<>();
+	private final State initialState = new State(0, 0, false, false);
+	@Nullable
+	private ContactId contactId = null;
+	@Nullable
+	private RemovableDriveTask task = null;
+	@Nullable
+	private Consumer<State> taskObserver = null;
 
 	@Inject
 	RemovableDriveViewModel(Application app,
 			RemovableDriveManager removableDriveManager) {
 		super(app);
-
 		this.manager = removableDriveManager;
 	}
 
-	String getFileName() {
-		SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd_HHmmss_SSS", US);
-		return sdf.format(new Date());
-	}
-
-
-	LiveData<State> write(ContactId contactId, Uri uri) {
-		TransportProperties p = new TransportProperties();
-		p.put(PROP_URI, uri.toString());
-		return observe(manager.startWriterTask(contactId, p));
-	}
-
-	LiveData<State> read(Uri uri) {
-		TransportProperties p = new TransportProperties();
-		p.put(PROP_URI, uri.toString());
-		return observe(manager.startReaderTask(p));
-	}
-
-	@Nullable
-	LiveData<State> ongoingWrite() {
-		RemovableDriveTask task = manager.getCurrentWriterTask();
-		if (task == null) {
-			return null;
-		}
-		return observe(task);
-	}
-
-	@Nullable
-	LiveData<State> ongoingRead() {
-		RemovableDriveTask task = manager.getCurrentReaderTask();
-		if (task == null) {
-			return null;
-		}
-		return observe(task);
-	}
-
-	private LiveData<State> observe(RemovableDriveTask task) {
-		MutableLiveData<State> state = new MutableLiveData<>();
-		Consumer<State> observer = state::postValue;
-		task.addObserver(observer);
-		observers.put(observer, task);
-		return state;
-	}
-
 	@Override
 	protected void onCleared() {
-		for (Map.Entry<Consumer<State>, RemovableDriveTask> entry
-				: observers.entrySet()) {
-			entry.getValue().removeObserver(entry.getKey());
+		if (task != null) {
+			// when we have a task, we must have an observer for it
+			Consumer<State> observer = requireNonNull(taskObserver);
+			task.removeObserver(observer);
 		}
 	}
+
+	/**
+	 * Set this as soon as it becomes available.
+	 */
+	void setContactId(ContactId contactId) {
+		this.contactId = contactId;
+	}
+
+	@UiThread
+	void startSendData() {
+		action.setEvent(Action.SEND);
+
+		// check if there is already a send/write task
+		task = manager.getCurrentWriterTask();
+		if (task == null) {
+			// TODO check if there is data to export now
+			//  and only allow to continue if there is.
+			state.setValue(new TransferDataState.Ready());
+		} else {
+			// observe old task and start with initial state
+			taskObserver = s -> observeTask(s, true);
+			taskObserver.accept(initialState);
+			task.addObserver(taskObserver);
+		}
+	}
+
+	@UiThread
+	void startReceiveData() {
+		action.setEvent(Action.RECEIVE);
+
+		// check if there is already a receive/read task
+		task = manager.getCurrentReaderTask();
+		if (task == null) {
+			state.setValue(new TransferDataState.Ready());
+		} else {
+			// observe old task and start with initial state
+			taskObserver = s -> observeTask(s, true);
+			taskObserver.accept(initialState);
+			task.addObserver(taskObserver);
+		}
+	}
+
+	@UiThread
+	private void observeTask(RemovableDriveTask.State s, boolean isOldTask) {
+		state.setValue(new TransferDataState.TaskAvailable(s, isOldTask));
+	}
+
+	String getFileName() {
+		SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd_HHmmss", US);
+		return sdf.format(new Date()) + ".zip";
+	}
+
+	/**
+	 * Call this only when in {@link TransferDataState.Ready}.
+	 */
+	@UiThread
+	void exportData(Uri uri) {
+		// starting an action more than once is not supported for simplicity
+		if (task != null) throw new IllegalStateException();
+
+		// from now on, we are not re-usable
+		taskObserver = s -> observeTask(s, false);
+		taskObserver.accept(initialState);
+
+		// start the writer task for this contact and observe it
+		TransportProperties p = new TransportProperties();
+		p.put(PROP_URI, uri.toString());
+		ContactId c = requireNonNull(contactId);
+		task = manager.startWriterTask(c, p);
+		task.addObserver(taskObserver);
+	}
+
+	/**
+	 * Call this only when in {@link TransferDataState.Ready}.
+	 */
+	@UiThread
+	void importData(Uri uri) {
+		// starting an action more than once is not supported for simplicity
+		if (task != null) throw new IllegalStateException();
+
+		// from now on, we are not re-usable
+		taskObserver = s -> observeTask(s, false);
+		taskObserver.accept(initialState);
+
+		TransportProperties p = new TransportProperties();
+		p.put(PROP_URI, uri.toString());
+		task = manager.startReaderTask(p);
+		task.addObserver(taskObserver);
+	}
+
+	LiveEvent<Action> getActionEvent() {
+		return action;
+	}
+
+	LiveData<TransferDataState> getState() {
+		return state;
+	}
+
 }

briar-android/src/main/java/org/briarproject/briar/android/removabledrive/SendFragment.java

@@ -0,0 +1,114 @@
+package org.briarproject.briar.android.removabledrive;
+
+import android.content.Context;
+import android.net.Uri;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+import android.widget.ProgressBar;
+import android.widget.TextView;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
+import org.briarproject.briar.R;
+
+import javax.inject.Inject;
+
+import androidx.activity.result.ActivityResultLauncher;
+import androidx.activity.result.contract.ActivityResultContracts.CreateDocument;
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+import androidx.fragment.app.FragmentActivity;
+import androidx.lifecycle.ViewModelProvider;
+
+import static android.view.View.GONE;
+import static android.view.View.VISIBLE;
+import static android.widget.Toast.LENGTH_LONG;
+import static org.briarproject.briar.android.AppModule.getAndroidComponent;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class SendFragment extends Fragment {
+
+	final static String TAG = SendFragment.class.getName();
+
+	private final ActivityResultLauncher<String> launcher =
+			registerForActivityResult(new CreateDocument(),
+					this::onDocumentCreated);
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	RemovableDriveViewModel viewModel;
+	TextView introTextView;
+	Button button;
+	ProgressBar progressBar;
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		FragmentActivity activity = requireActivity();
+		getAndroidComponent(activity).inject(this);
+		viewModel = new ViewModelProvider(activity, viewModelFactory)
+				.get(RemovableDriveViewModel.class);
+	}
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View v = inflater.inflate(R.layout.fragment_transfer_data_send,
+				container, false);
+
+		introTextView = v.findViewById(R.id.introTextView);
+		progressBar = v.findViewById(R.id.progressBar);
+		button = v.findViewById(R.id.fileButton);
+		button.setOnClickListener(view ->
+				launcher.launch(viewModel.getFileName())
+		);
+
+		viewModel.getState()
+				.observe(getViewLifecycleOwner(), this::onStateChanged);
+
+		return v;
+	}
+
+	@Override
+	public void onStart() {
+		super.onStart();
+		requireActivity().setTitle(R.string.removable_drive_title_send);
+	}
+
+	private void onStateChanged(TransferDataState state) {
+		if (state instanceof TransferDataState.NoDataToSend) {
+			introTextView.setText(R.string.removable_drive_send_no_data);
+			button.setVisibility(GONE);
+		} else if (state instanceof TransferDataState.Ready) {
+			button.setVisibility(VISIBLE);
+		} else if (state instanceof TransferDataState.TaskAvailable) {
+			button.setEnabled(false);
+			if (((TransferDataState.TaskAvailable) state).isOldTask) {
+				Toast.makeText(requireContext(),
+						R.string.removable_drive_ongoing, LENGTH_LONG).show();
+			}
+			RemovableDriveTask.State s =
+					((TransferDataState.TaskAvailable) state).state;
+			if (s.getTotal() > 0L && progressBar.getVisibility() != VISIBLE) {
+				progressBar.setVisibility(VISIBLE);
+				// FIXME if we ever export more than 2 GB, this won't work
+				progressBar.setMax((int) s.getTotal());
+			}
+			progressBar.setProgress((int) s.getDone());
+		}
+	}
+
+	private void onDocumentCreated(@Nullable Uri uri) {
+		if (uri == null) return;
+		viewModel.exportData(uri);
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/removabledrive/TransferDataModule.java

@@ -8,11 +8,12 @@ import dagger.Module;
 import dagger.multibindings.IntoMap;
 
 @Module
-public interface RemovableDriveModule {
+public interface TransferDataModule {
 
 	@Binds
 	@IntoMap
 	@ViewModelKey(RemovableDriveViewModel.class)
-	ViewModel bindRemovableDriveViewModel(RemovableDriveViewModel removableDriveViewModel);
+	ViewModel bindRemovableDriveViewModel(
+			RemovableDriveViewModel removableDriveViewModel);
 
 }

briar-android/src/main/java/org/briarproject/briar/android/removabledrive/TransferDataState.java

@@ -0,0 +1,39 @@
+package org.briarproject.briar.android.removabledrive;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
+
+@NotNullByDefault
+abstract class TransferDataState {
+
+	/**
+	 * There is nothing we can send to the chosen contact.
+	 * This only applies to sending data, but not to receiving it.
+	 */
+	static class NoDataToSend extends TransferDataState {
+	}
+
+	/**
+	 * We are ready to let the user select a file for sending or receiving data.
+	 */
+	static class Ready extends TransferDataState {
+	}
+
+	/**
+	 * A task with state information is available and should be shown in the UI.
+	 */
+	static class TaskAvailable extends TransferDataState {
+		final RemovableDriveTask.State state;
+		/**
+		 * This is an old task that is still ongoing. The user needs to wait for
+		 * it to complete before starting a new task.
+		 */
+		final boolean isOldTask;
+
+		TaskAvailable(RemovableDriveTask.State state, boolean isOldTask) {
+			this.state = state;
+			this.isOldTask = isOldTask;
+		}
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/util/UiUtils.java

@@ -58,7 +58,9 @@ import androidx.core.content.ContextCompat;
 import androidx.core.hardware.fingerprint.FingerprintManagerCompat;
 import androidx.core.text.HtmlCompat;
 import androidx.core.util.Consumer;
+import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentActivity;
+import androidx.fragment.app.FragmentManager;
 import androidx.lifecycle.LifecycleOwner;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.Observer;
@@ -139,6 +141,17 @@ public class UiUtils {
 		imm.hideSoftInputFromWindow(view.getWindowToken(), 0);
 	}
 
+	public static void showFragment(FragmentManager fm, Fragment f,
+			@Nullable String tag) {
+		fm.beginTransaction()
+				.setCustomAnimations(R.anim.step_next_in,
+						R.anim.step_previous_out, R.anim.step_previous_in,
+						R.anim.step_next_out)
+				.replace(R.id.fragmentContainer, f, tag)
+				.addToBackStack(tag)
+				.commit();
+	}
+
 	public static String getContactDisplayName(Author author,
 			@Nullable String alias) {
 		String name = author.getName();