improve threshold choosing UI

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/CustodianHelpRecoverActivity.java

@@ -11,7 +11,6 @@ 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;
-import org.briarproject.briar.api.socialbackup.BackupMetadata;
 import org.briarproject.briar.api.socialbackup.SocialBackupManager;
 
 import javax.inject.Inject;
@@ -41,7 +40,7 @@ public class CustodianHelpRecoverActivity extends BriarActivity implements
 		if (id == -1) throw new IllegalStateException("No ContactId");
 		ContactId contactId = new ContactId(id);
 
-        // check if we have a shard for this secret owner
+		// check if we have a shard for this secret owner
 		try {
 			db.transaction(false, txn -> {
 				if (!socialBackupManager.amCustodian(txn, contactId)) {

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/DistributedBackupActivity.java

@@ -64,11 +64,6 @@ public class DistributedBackupActivity extends BriarActivity implements
 				String.format("selected %d contacts", contacts.size()),
 				Toast.LENGTH_SHORT).show();
 		custodians = contacts;
-		if (contacts.size() < 4) {
-			// For 2 or 3 contacts, there is no choice of threshold
-			thresholdDefined(2);
-			return;
-		}
 		ThresholdSelectorFragment fragment =
 				ThresholdSelectorFragment.newInstance(contacts.size());
 		showNextFragment(fragment);

briar-android/src/main/java/org/briarproject/briar/android/socialbackup/ThresholdSelectorFragment.java

@@ -27,7 +27,6 @@ public class ThresholdSelectorFragment extends BaseFragment {
 
 	protected ThresholdDefinedListener listener;
 
-	// TODO this should be the actual number of custodians
 	private int numberOfCustodians;
 	private int threshold;
 	private int recommendedThreshold;
@@ -59,20 +58,31 @@ public class ThresholdSelectorFragment extends BaseFragment {
 				container, false);
 		Bundle args = requireArguments();
 		numberOfCustodians = args.getInt(NUMBER_CUSTODIANS);
-
 		seekBar = view.findViewById(R.id.seekBar);
 		thresholdRepresentation =
 				view.findViewById(R.id.textViewThresholdRepresentation);
 		message = view.findViewById(R.id.textViewMessage);
 		mOfn = view.findViewById(R.id.textViewmOfn);
-		int max = numberOfCustodians - 3;
-		seekBar.setMax(max);
-		seekBar.setOnSeekBarChangeListener(new SeekBarListener());
-		recommendedThreshold =
-				SecretSharingWrapper.defaultThreshold(numberOfCustodians);
-		threshold = recommendedThreshold;
-		seekBar.setProgress(threshold - 2);
 
+		if (numberOfCustodians == 2) {
+			message.setText(R.string.threshold_too_few_custodians);
+		}
+		if (numberOfCustodians > 3) {
+			seekBar.setMax(numberOfCustodians -3);
+			seekBar.setProgress(threshold - 2);
+			seekBar.setOnSeekBarChangeListener(new SeekBarListener());
+			recommendedThreshold =
+					SecretSharingWrapper.defaultThreshold(numberOfCustodians);
+			threshold = recommendedThreshold;
+
+		} else {
+			seekBar.setEnabled(false);
+			threshold = 2;
+			seekBar.setMax(numberOfCustodians);
+			seekBar.setProgress(threshold);
+			TextView t = view.findViewById(R.id.title_threshold);
+			t.setText(R.string.threshold_disabled);
+		}
 		thresholdRepresentation.setText(buildThresholdRepresentationString());
 		setmOfnText();
 		return view;
@@ -81,7 +91,7 @@ public class ThresholdSelectorFragment extends BaseFragment {
 
 	private void setmOfnText() {
 		mOfn.setText(String.format(
-				"%d of %d contacts needed to recover your account", threshold,
+				getString(R.string.threshold_m_of_n), threshold,
 				numberOfCustodians));
 	}
 

briar-android/src/main/res/values/strings.xml

@@ -655,12 +655,15 @@
 	<string name="select_at_least_n_contacts">Please select at least %d contacts</string>
 	<string name="select_at_least_n_more_contacts">Please select at least %d more contacts</string>
 
-	<string name="threshold">The minimum number of trusted contacts needed to restore your account:</string>
+	<string name="threshold">Choose the minimum number of trusted contacts needed to restore your account</string>
+	<string name="threshold_disabled">Two trusted contacts will be needed to restore your account</string>
 	<string name="threshold_secure">Secure</string>
 	<string name="threshold_recommended">Secure - recommended threshold</string>
 	<string name="threshold_low_insecure">Insecure – higher threshold recommended</string>
 	<string name="threshold_high_insecure">Danger of loss – lower threshold recommended</string>
+	<string name="threshold_too_few_custodians">Danger of loss - more contacts recommended</string>
 	<string name="threshold_defined">Choose Threshold</string>
+	<string name="threshold_m_of_n">%d of %d contacts needed to recover your account</string>
 
 	<string name="backup_done_info">Backup pieces sent to trusted contacts</string>
 	<string name="backup_done_dismiss">Got it</string>
@@ -691,7 +694,7 @@
 
 	<string name="title_distributed_backup">Social Backup</string>
 	<string name="title_select_custodians">Select Trusted Contacts</string>
-	<string name="title_define_threshold">Choose Threshold</string>
+	<string name="title_define_threshold">Threshold</string>
 	<string name="title_recovery_mode">Recovery Mode</string>
 	<string name="title_help_recover">Help recover account</string>