diff --git a/app/src/main/kotlin/jackall/moncalc/App.kt b/app/src/main/kotlin/jackall/moncalc/App.kt
index 24d255a..e19bc6a 100644
--- a/app/src/main/kotlin/jackall/moncalc/App.kt
+++ b/app/src/main/kotlin/jackall/moncalc/App.kt
@@ -1,12 +1,15 @@
 package jackall.moncalc
 
 import android.annotation.SuppressLint
+import android.app.Activity
 import android.app.Application
+import android.os.Bundle
 
 /**
  * Created by matsumoto_k on 2017/11/01.
  */
 class App : Application() {
+    var currentActivity: Activity? = null
 
     companion object {
         @SuppressLint("StaticFieldLeak")
@@ -17,5 +20,36 @@
     override fun onCreate() {
         super.onCreate()
         instance = this
+        registerActivityLifecycleCallbacks(object : Application.ActivityLifecycleCallbacks {
+            override fun onActivityCreated(activity: Activity, saveInstanceState: Bundle?) {
+
+            }
+
+            override fun onActivityStarted(activity: Activity) {
+                currentActivity = activity
+            }
+
+            override fun onActivityResumed(activity: Activity) {
+
+            }
+
+            override fun onActivityPaused(activity: Activity) {
+
+            }
+
+            override fun onActivityStopped(activity: Activity) {
+                if (currentActivity === activity) {
+                    currentActivity = null
+                }
+            }
+
+            override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle?) {
+
+            }
+
+            override fun onActivityDestroyed(activity: Activity) {
+
+            }
+        })
     }
 }
\ No newline at end of file