diff --git a/.gitignore b/.gitignore
index c6cbe56..5f94008 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,8 +1,7 @@
 *.iml
 .gradle
 /local.properties
-/.idea/workspace.xml
-/.idea/libraries
+/.idea
 .DS_Store
 /build
 /captures
diff --git a/.idea/compiler.xml b/.idea/compiler.xml
deleted file mode 100644
index 96cc43e..0000000
--- a/.idea/compiler.xml
+++ /dev/null
@@ -1,22 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="CompilerConfiguration">
-    <resourceExtensions />
-    <wildcardResourcePatterns>
-      <entry name="!?*.java" />
-      <entry name="!?*.form" />
-      <entry name="!?*.class" />
-      <entry name="!?*.groovy" />
-      <entry name="!?*.scala" />
-      <entry name="!?*.flex" />
-      <entry name="!?*.kt" />
-      <entry name="!?*.clj" />
-      <entry name="!?*.aj" />
-    </wildcardResourcePatterns>
-    <annotationProcessing>
-      <profile default="true" name="Default" enabled="false">
-        <processorPath useClasspath="true" />
-      </profile>
-    </annotationProcessing>
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/copyright/profiles_settings.xml b/.idea/copyright/profiles_settings.xml
deleted file mode 100644
index e7bedf3..0000000
--- a/.idea/copyright/profiles_settings.xml
+++ /dev/null
@@ -1,3 +0,0 @@
-<component name="CopyrightManager">
-  <settings default="" />
-</component>
\ No newline at end of file
diff --git a/.idea/encodings.xml b/.idea/encodings.xml
deleted file mode 100644
index 97626ba..0000000
--- a/.idea/encodings.xml
+++ /dev/null
@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="Encoding">
-    <file url="PROJECT" charset="UTF-8" />
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/gradle.xml b/.idea/gradle.xml
deleted file mode 100644
index fc8049c..0000000
--- a/.idea/gradle.xml
+++ /dev/null
@@ -1,27 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="GradleSettings">
-    <option name="linkedExternalProjectsSettings">
-      <GradleProjectSettings>
-        <option name="distributionType" value="DEFAULT_WRAPPED" />
-        <option name="externalProjectPath" value="$PROJECT_DIR$" />
-        <option name="gradleHome" value="$APPLICATION_HOME_DIR$/gradle/gradle-2.8" />
-        <option name="gradleJvm" value="1.8" />
-        <option name="modules">
-          <set>
-            <option value="$PROJECT_DIR$" />
-            <option value="$PROJECT_DIR$/library" />
-            <option value="$PROJECT_DIR$/sample" />
-          </set>
-        </option>
-        <option name="myModules">
-          <set>
-            <option value="$PROJECT_DIR$" />
-            <option value="$PROJECT_DIR$/library" />
-            <option value="$PROJECT_DIR$/sample" />
-          </set>
-        </option>
-      </GradleProjectSettings>
-    </option>
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
deleted file mode 100644
index 5d19981..0000000
--- a/.idea/misc.xml
+++ /dev/null
@@ -1,46 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="EntryPointsManager">
-    <entry_points version="2.0" />
-  </component>
-  <component name="NullableNotNullManager">
-    <option name="myDefaultNullable" value="android.support.annotation.Nullable" />
-    <option name="myDefaultNotNull" value="android.support.annotation.NonNull" />
-    <option name="myNullables">
-      <value>
-        <list size="4">
-          <item index="0" class="java.lang.String" itemvalue="org.jetbrains.annotations.Nullable" />
-          <item index="1" class="java.lang.String" itemvalue="javax.annotation.Nullable" />
-          <item index="2" class="java.lang.String" itemvalue="edu.umd.cs.findbugs.annotations.Nullable" />
-          <item index="3" class="java.lang.String" itemvalue="android.support.annotation.Nullable" />
-        </list>
-      </value>
-    </option>
-    <option name="myNotNulls">
-      <value>
-        <list size="4">
-          <item index="0" class="java.lang.String" itemvalue="org.jetbrains.annotations.NotNull" />
-          <item index="1" class="java.lang.String" itemvalue="javax.annotation.Nonnull" />
-          <item index="2" class="java.lang.String" itemvalue="edu.umd.cs.findbugs.annotations.NonNull" />
-          <item index="3" class="java.lang.String" itemvalue="android.support.annotation.NonNull" />
-        </list>
-      </value>
-    </option>
-  </component>
-  <component name="ProjectLevelVcsManager" settingsEditedManually="false">
-    <OptionsSetting value="true" id="Add" />
-    <OptionsSetting value="true" id="Remove" />
-    <OptionsSetting value="true" id="Checkout" />
-    <OptionsSetting value="true" id="Update" />
-    <OptionsSetting value="true" id="Status" />
-    <OptionsSetting value="true" id="Edit" />
-    <ConfirmationsSetting value="0" id="Add" />
-    <ConfirmationsSetting value="0" id="Remove" />
-  </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_7" default="true" assert-keyword="true" jdk-15="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
-    <output url="file://$PROJECT_DIR$/build/classes" />
-  </component>
-  <component name="ProjectType">
-    <option name="id" value="Android" />
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/modules.xml b/.idea/modules.xml
deleted file mode 100644
index 52176cb..0000000
--- a/.idea/modules.xml
+++ /dev/null
@@ -1,10 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="ProjectModuleManager">
-    <modules>
-      <module fileurl="file://$PROJECT_DIR$/PreferencesManager.iml" filepath="$PROJECT_DIR$/PreferencesManager.iml" />
-      <module fileurl="file://$PROJECT_DIR$/library/library.iml" filepath="$PROJECT_DIR$/library/library.iml" />
-      <module fileurl="file://$PROJECT_DIR$/sample/sample.iml" filepath="$PROJECT_DIR$/sample/sample.iml" />
-    </modules>
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/runConfigurations.xml b/.idea/runConfigurations.xml
deleted file mode 100644
index 7f68460..0000000
--- a/.idea/runConfigurations.xml
+++ /dev/null
@@ -1,12 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="RunConfigurationProducerService">
-    <option name="ignoredProducers">
-      <set>
-        <option value="org.jetbrains.plugins.gradle.execution.test.runner.AllInPackageGradleConfigurationProducer" />
-        <option value="org.jetbrains.plugins.gradle.execution.test.runner.TestClassGradleConfigurationProducer" />
-        <option value="org.jetbrains.plugins.gradle.execution.test.runner.TestMethodGradleConfigurationProducer" />
-      </set>
-    </option>
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
deleted file mode 100644
index 94a25f7..0000000
--- a/.idea/vcs.xml
+++ /dev/null
@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="VcsDirectoryMappings">
-    <mapping directory="$PROJECT_DIR$" vcs="Git" />
-  </component>
-</project>
\ No newline at end of file
diff --git a/library/build.gradle b/library/build.gradle
index b221b8d..3b27449 100644
--- a/library/build.gradle
+++ b/library/build.gradle
@@ -20,7 +20,7 @@ android {
 }
 
 dependencies {
-    compile 'com.google.code.gson:gson:2.6.2'
+    compile 'com.google.code.gson:gson:2.7'
 }
 
 publish {
diff --git a/library/src/main/java/com/shawnlin/preferencesmanager/PreferencesManager.java b/library/src/main/java/com/shawnlin/preferencesmanager/PreferencesManager.java
index 08e5a15..c708114 100644
--- a/library/src/main/java/com/shawnlin/preferencesmanager/PreferencesManager.java
+++ b/library/src/main/java/com/shawnlin/preferencesmanager/PreferencesManager.java
@@ -344,4 +344,26 @@ public static void clear() {
         mSharedPreferences.edit().clear().apply();
     }
 
+    /**
+     * Registers a callback to be invoked when a change happens to a preference.
+     * @param listener The callback that will run.
+     */
+    public static void registerOnChangeListener(SharedPreferences.OnSharedPreferenceChangeListener listener) {
+        if (mSharedPreferences == null) {
+            return;
+        }
+        mSharedPreferences.registerOnSharedPreferenceChangeListener(listener);
+    }
+
+    /**
+     * Unregisters a previous callback.
+     * @param listener The callback that should be unregistered.
+     */
+    public static void unregisterOnChangeListener(SharedPreferences.OnSharedPreferenceChangeListener listener) {
+        if (mSharedPreferences == null) {
+            return;
+        }
+        mSharedPreferences.unregisterOnSharedPreferenceChangeListener(listener);
+    }
+
 }