Check if the external storage is accessible before writing

app/src/main/java/org/shadowice/flocke/andotp/MainActivity.java

@@ -106,10 +106,16 @@ public class MainActivity extends AppCompatActivity {
     }
 
     private void doExportJSON() {
-        boolean success = SettingsHelper.exportAsJSON(this);
+        if (StorageHelper.isExternalStorageWritable()) {
+            boolean success = SettingsHelper.exportAsJSON(this);
 
-        if (success)
-            showSimpleSnackbar(R.string.msg_export_success);
+            if (success)
+                showSimpleSnackbar(R.string.msg_export_success);
+            else
+                showSimpleSnackbar(R.string.msg_export_failed);
+        } else {
+            showSimpleSnackbar(R.string.msg_storage_not_accessible);
+        }
     }
 
     private void exportJSON() {

app/src/main/java/org/shadowice/flocke/andotp/StorageHelper.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2017 Jakob Nixdorf
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package org.shadowice.flocke.andotp;
+
+import android.os.Environment;
+
+public class StorageHelper {
+    /* Checks if external storage is available for read and write */
+    public static boolean isExternalStorageWritable() {
+        String state = Environment.getExternalStorageState();
+        if (Environment.MEDIA_MOUNTED.equals(state)) {
+            return true;
+        }
+        return false;
+    }
+
+    /* Checks if external storage is available to at least read */
+    public static boolean isExternalStorageReadable() {
+        String state = Environment.getExternalStorageState();
+        if (Environment.MEDIA_MOUNTED.equals(state) ||
+                Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
+            return true;
+        }
+        return false;
+    }
+}

app/src/main/res/values/strings.xml

@@ -27,6 +27,8 @@
         This file contains all your secret keys, please keep it safe!
     </string>
     <string name="msg_export_success">Export to external storage successful</string>
+    <string name="msg_export_failed">Export to external storage failed</string>
+    <string name="msg_storage_not_accessible">External storage currently not accessible</string>
 
     <!-- About dialog -->
     <string name="about_description">An open-source two-factor authentication App for Android 4.3+</string>