diff --git a/android/build.gradle b/android/build.gradle
index 0df2518..f5c97cb 100644
--- a/android/build.gradle
+++ b/android/build.gradle
@@ -2,7 +2,7 @@ group 'com.flutter.moum.screenshot_callback'
 version '1.0'
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.20'
 
     repositories {
         google()
@@ -37,8 +37,14 @@ android {
     }
 }
 
+configurations.all {
+    resolutionStrategy {
+        force 'androidx.core:core-ktx:1.6.0'
+    }
+}
+
 dependencies {
-    implementation "androidx.core:core-ktx:1.7.0"
+    implementation "androidx.core:core-ktx:1.6.0"
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
 }
 
diff --git a/android/gradle/wrapper/gradle-wrapper.properties b/android/gradle/wrapper/gradle-wrapper.properties
index 3c46198..3c472b9 100644
--- a/android/gradle/wrapper/gradle-wrapper.properties
+++ b/android/gradle/wrapper/gradle-wrapper.properties
@@ -2,4 +2,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.5-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.5-all.zip
diff --git a/android/src/main/java/com/flutter/moum/screenshot_callback/ScreenshotCallbackPlugin.java b/android/src/main/java/com/flutter/moum/screenshot_callback/ScreenshotCallbackPlugin.java
index 48cab55..36788ce 100644
--- a/android/src/main/java/com/flutter/moum/screenshot_callback/ScreenshotCallbackPlugin.java
+++ b/android/src/main/java/com/flutter/moum/screenshot_callback/ScreenshotCallbackPlugin.java
@@ -4,16 +4,14 @@
 import android.os.Handler;
 import android.os.Looper;
 
+import androidx.annotation.NonNull;
+
+import io.flutter.embedding.engine.plugins.FlutterPlugin;
+import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
 import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
 import io.flutter.plugin.common.MethodChannel.Result;
-import io.flutter.embedding.engine.plugins.FlutterPlugin;
-import io.flutter.plugin.common.BinaryMessenger;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
-
 import kotlin.Unit;
 import kotlin.jvm.functions.Function1;
 
@@ -41,8 +39,10 @@ private void onAttachedToEngine(Context applicationContext, BinaryMessenger mess
     @Override
     public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
         applicationContext = null;
-        channel.setMethodCallHandler(null);
-        channel = null;
+        if (channel != null) {
+            channel.setMethodCallHandler(null);
+            channel = null;
+        }
     }
 
     @Override
diff --git a/example/pubspec.lock b/example/pubspec.lock
index f138bfa..4d9d44a 100644
--- a/example/pubspec.lock
+++ b/example/pubspec.lock
@@ -5,51 +5,44 @@ packages:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.8.2"
+    version: "2.9.0"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.0"
   characters:
     dependency: transitive
     description:
       name: characters
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.2.0"
-  charcode:
-    dependency: transitive
-    description:
-      name: charcode
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.3.1"
+    version: "1.2.1"
   clock:
     dependency: transitive
     description:
       name: clock
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.0"
+    version: "1.1.1"
   collection:
     dependency: transitive
     description:
       name: collection
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.16.0"
   fake_async:
     dependency: transitive
     description:
       name: fake_async
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.3.0"
+    version: "1.3.1"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -64,37 +57,37 @@ packages:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.12.11"
+    version: "0.12.12"
   material_color_utilities:
     dependency: transitive
     description:
       name: material_color_utilities
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.1.4"
+    version: "0.1.5"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.0"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.8.1"
+    version: "1.8.2"
   screenshot_callback:
     dependency: "direct dev"
     description:
       path: ".."
       relative: true
     source: path
-    version: "2.0.1"
+    version: "2.0.3"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -104,49 +97,49 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.8.2"
+    version: "1.9.0"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.10.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.0"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.0"
+    version: "1.1.1"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.2.0"
+    version: "1.2.1"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.4.9"
+    version: "0.4.12"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.2"
 sdks:
diff --git a/pubspec.lock b/pubspec.lock
index a461bdf..6c977b0 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -5,51 +5,44 @@ packages:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.8.2"
+    version: "2.9.0"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.0"
   characters:
     dependency: transitive
     description:
       name: characters
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.2.0"
-  charcode:
-    dependency: transitive
-    description:
-      name: charcode
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.3.1"
+    version: "1.2.1"
   clock:
     dependency: transitive
     description:
       name: clock
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.0"
+    version: "1.1.1"
   collection:
     dependency: transitive
     description:
       name: collection
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.16.0"
   fake_async:
     dependency: transitive
     description:
       name: fake_async
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.3.0"
+    version: "1.3.1"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -64,30 +57,30 @@ packages:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.12.11"
+    version: "0.12.12"
   material_color_utilities:
     dependency: transitive
     description:
       name: material_color_utilities
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.1.4"
+    version: "0.1.5"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.0"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.8.1"
+    version: "1.8.2"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -97,49 +90,49 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.8.2"
+    version: "1.9.0"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.10.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.0"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.0"
+    version: "1.1.1"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.2.0"
+    version: "1.2.1"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.4.9"
+    version: "0.4.12"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.2"
 sdks: