diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 0d55985..ecdf514 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -7,7 +7,8 @@
 	<uses-permission android:name="android.permission.INTERNET"/>
 	<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
 
-	<application android:icon="@drawable/icon" android:label="@string/app_name" android:theme="@style/Theme.Sherlock.Light">
+	<application android:icon="@drawable/icon" android:label="@string/app_name"
+	             android:theme="@style/Theme.Sherlock.Light.DarkActionBar">
 		<activity android:name=".ui.MainActivity">
 			<intent-filter>
 				<action android:name="android.intent.action.MAIN"/>
diff --git a/src/main/java/com/github/hoverruan/libr/mobile/domain/Book.java b/src/main/java/com/github/hoverruan/libr/mobile/domain/Book.java
index 19cb701..b17d848 100644
--- a/src/main/java/com/github/hoverruan/libr/mobile/domain/Book.java
+++ b/src/main/java/com/github/hoverruan/libr/mobile/domain/Book.java
@@ -69,4 +69,14 @@ public class Book {
     public void setName(String name) {
         this.name = name;
     }
+
+    public String buildFilename() {
+        StringBuilder builder = new StringBuilder(isbn);
+        int pos = image.lastIndexOf('.');
+        if (pos > 0) {
+            String suffix = image.substring(pos);
+            builder.append(suffix);
+        }
+        return builder.toString();
+    }
 }
diff --git a/src/main/java/com/github/hoverruan/libr/mobile/ui/MainActivity.java b/src/main/java/com/github/hoverruan/libr/mobile/ui/MainActivity.java
index 5b4be8d..f77ceb5 100644
--- a/src/main/java/com/github/hoverruan/libr/mobile/ui/MainActivity.java
+++ b/src/main/java/com/github/hoverruan/libr/mobile/ui/MainActivity.java
@@ -21,6 +21,7 @@ import com.github.hoverruan.libr.mobile.domain.BookList;
 import com.github.hoverruan.libr.mobile.domain.BookParser;
 import com.github.hoverruan.libr.mobile.util.DownloadImageTask;
 import com.github.hoverruan.libr.mobile.util.DownloadJsonTask;
+import static com.github.hoverruan.libr.mobile.util.FileUtils.newFile;
 
 import java.io.File;
 import java.util.List;
@@ -37,7 +38,7 @@ public class MainActivity extends SherlockListActivity {
 
         requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
 
-        setSupportProgressBarIndeterminateVisibility(true);
+//        setSupportProgressBarIndeterminateVisibility(true);
         new DownloadBooksInfo().execute("http://libr.herokuapp.com/api/books");
     }
 
@@ -100,7 +101,7 @@ public class MainActivity extends SherlockListActivity {
                     setListAdapter(new BookListAdapter(MainActivity.this));
                 }
             }
-            setSupportProgressBarIndeterminateVisibility(false);
+//            setSupportProgressBarIndeterminateVisibility(false);
         }
     }
 
@@ -114,15 +115,15 @@ public class MainActivity extends SherlockListActivity {
         }
 
         public void load() {
-            File imageFile = DownloadImageTask.calculateImageFile(MainActivity.this, "cover", book.getIsbn());
-            if (!imageFile.exists()) {
-                new DownloadImageTask(MainActivity.this, "cover", book.getIsbn()) {
+            File coverFile = newFile(MainActivity.this.getCacheDir(), "cover", book.buildFilename());
+            if (!coverFile.exists()) {
+                new DownloadImageTask(MainActivity.this, coverFile) {
                     protected void onPostExecute(File downloadedImageFile) {
                         loadImage(downloadedImageFile);
                     }
                 }.execute(book.getImage());
             } else {
-                loadImage(imageFile);
+                loadImage(coverFile);
             }
         }
 
diff --git a/src/main/java/com/github/hoverruan/libr/mobile/util/FileUtils.java b/src/main/java/com/github/hoverruan/libr/mobile/util/FileUtils.java
new file mode 100644
index 0000000..f1b311a
--- /dev/null
+++ b/src/main/java/com/github/hoverruan/libr/mobile/util/FileUtils.java
@@ -0,0 +1,18 @@
+package com.github.hoverruan.libr.mobile.util;
+
+import java.io.File;
+
+/**
+ * @author Hover Ruan
+ */
+public class FileUtils {
+    public static File newFile(File root, String... paths) {
+        File targetFile = root;
+
+        for (String path : paths) {
+            targetFile = new File(targetFile, path);
+        }
+
+        return targetFile;
+    }
+}
diff --git a/src/test/java/com/github/hoverruan/libr/mobile/domain/BookTest.java b/src/test/java/com/github/hoverruan/libr/mobile/domain/BookTest.java
new file mode 100644
index 0000000..e0e8fa4
--- /dev/null
+++ b/src/test/java/com/github/hoverruan/libr/mobile/domain/BookTest.java
@@ -0,0 +1,24 @@
+package com.github.hoverruan.libr.mobile.domain;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+import org.junit.Test;
+
+/**
+ * @author Hover Ruan
+ */
+public class BookTest {
+    @Test
+    public void should_build_Filename_with_ISBN_and_image_url() {
+        String suffix = ".jpg";
+        String image = "http://img3.douban.com/mpic/s4483293" + suffix;
+        String isbn = "9787111316657";
+
+        Book book = new Book();
+        book.setImage(image);
+        book.setIsbn(isbn);
+
+        String filename = book.buildFilename();
+        assertThat(filename, is(isbn + suffix));
+    }
+}