Address review comments

briar-android/src/org/briarproject/android/sharing/ShareForumActivity.java

@@ -0,0 +1,51 @@
+package org.briarproject.android.sharing;
+
+import org.briarproject.R;
+import org.briarproject.android.ActivityComponent;
+import org.briarproject.api.contact.Contact;
+import org.briarproject.api.contact.ContactId;
+import org.briarproject.api.db.DbException;
+import org.briarproject.api.forum.ForumSharingManager;
+import org.briarproject.api.sync.GroupId;
+
+import javax.inject.Inject;
+
+import static org.briarproject.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+
+public class ShareForumActivity extends ShareActivity {
+
+	// Fields that are accessed from background threads must be volatile
+	@Inject
+	volatile ForumSharingManager forumSharingManager;
+
+	@Override
+	BaseMessageFragment getMessageFragment() {
+		return ShareForumMessageFragment.newInstance();
+	}
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public boolean isDisabled(GroupId groupId, Contact c) throws DbException {
+		return !forumSharingManager.canBeShared(groupId, c);
+	}
+
+	@Override
+	protected void share(GroupId g, ContactId c, String msg)
+			throws DbException {
+		forumSharingManager.sendInvitation(g, c, msg);
+	}
+
+	@Override
+	protected int getSharingError() {
+		return R.string.forum_share_error;
+	}
+
+	@Override
+	public int getMaximumMessageLength() {
+		return MAX_MESSAGE_BODY_LENGTH;
+	}
+}