1.先導入函示庫(build.gradle: Module)

dependencies {
    implementation 'com.takwolf.android:foreback:0.1.1'
}

2.創建一個類別繼承Application並實現Foreback.Listener

import android.app.Activity
import android.app.Application
import android.util.Log
import com.takwolf.android.foreback.Foreback

class MyApplication : Application(), Foreback.Listener {

   override fun onCreate() {
       super.onCreate()
       Foreback.init(this)
       Foreback.registerListener(this)
  }

   override fun onApplicationEnterForeground(activity: Activity?) {
       Toast.makeText(activity, "前台", Toast.LENGTH_SHORT).show()
   }

  override fun onApplicationEnterBackground(activity: Activity?) {
      Toast.makeText(activity, "後台", Toast.LENGTH_SHORT).show()
  }
}

3.到AndroidManifest.xml註冊 已繼承Application跟實現Foreback.Listener的類別

<application
       android:name=".MyApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
       android:theme="@style/AppTheme">
       <activity android:name=".MainActivity">
          <intent-filter>
             <action android:name="android.intent.action.MAIN" />

               <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
  </application>

4.效果展示