diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index ff9ac9d57..016fc58c6 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -60,6 +60,7 @@
 
         <activity android:name="com.seafile.seadroid2.ui.activity.BrowserActivity"
                   android:label="@string/app_name"
+                  android:configChanges="orientation"
                   android:launchMode="singleTop">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
diff --git a/app/src/main/java/com/seafile/seadroid2/data/DataManager.java b/app/src/main/java/com/seafile/seadroid2/data/DataManager.java
index 94909e683..18269258f 100644
--- a/app/src/main/java/com/seafile/seadroid2/data/DataManager.java
+++ b/app/src/main/java/com/seafile/seadroid2/data/DataManager.java
@@ -488,6 +488,9 @@ public synchronized File getFileByBlocks(String repoName, String repoID, String
         }
 
         final Pair<String, String> pair = getRepoEncKey(repoID);
+        if (pair == null) {
+            throw SeafException.decryptException;
+        }
         final String encKey = pair.first;
         final String encIv = pair.second;
         if (TextUtils.isEmpty(encKey) || TextUtils.isEmpty(encIv)) {
@@ -646,6 +649,9 @@ public List<SeafCachedFile> getCachedFiles() {
     }
 
     public void addCachedFile(String repoName, String repoID, String path, String fileID, File file) {
+        if (file == null) {
+            return;
+        }
         // notify Android Gallery that a new file has appeared
 
         // file does not always reside in Seadroid directory structure (e.g. camera upload)
diff --git a/app/src/main/java/com/seafile/seadroid2/ui/activity/BrowserActivity.java b/app/src/main/java/com/seafile/seadroid2/ui/activity/BrowserActivity.java
index 462b07aaa..18f4e6939 100644
--- a/app/src/main/java/com/seafile/seadroid2/ui/activity/BrowserActivity.java
+++ b/app/src/main/java/com/seafile/seadroid2/ui/activity/BrowserActivity.java
@@ -1557,6 +1557,10 @@ else if (which == 1) // create folder
      * @param fileName
      */
     public void downloadFile(String dir, String fileName) {
+        // txService maybe null if layout orientation has changed
+        if (txService == null) {
+            return;
+        }
         String filePath = Utils.pathJoin(dir, fileName);
         txService.addDownloadTask(account,
                 navContext.getRepoName(),
@@ -1700,6 +1704,10 @@ protected void onPostExecute(List<SeafDirent> dirents) {
     }
 
     private void startFileActivity(String repoName, String repoID, String filePath, long fileSize) {
+        // txService maybe null if layout orientation has changed
+        if (txService == null) {
+            return;
+        }
         int taskID = txService.addDownloadTask(account, repoName, repoID, filePath, fileSize);
         Intent intent = new Intent(this, FileActivity.class);
         intent.putExtra("repoName", repoName);