add kotlin version

KotlinSample/app/build.gradle.kts

@@ -45,4 +45,6 @@ dependencies {
     testImplementation(libs.junit)
     androidTestImplementation(libs.androidx.junit)
     androidTestImplementation(libs.androidx.espresso.core)
+
+    implementation("com.google.android.gms:play-services-time:16.0.1")
 }

KotlinSample/app/src/main/AndroidManifest.xml

@@ -1,17 +1,16 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:tools="http://schemas.android.com/tools">
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
 
     <application
+        android:name=".MyApp"
         android:allowBackup="true"
         android:dataExtractionRules="@xml/data_extraction_rules"
         android:fullBackupContent="@xml/backup_rules"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"
         android:roundIcon="@mipmap/ic_launcher_round"
         android:supportsRtl="true"
-        android:theme="@style/Theme.KotlinSample"
-        tools:targetApi="31">
+        android:theme="@style/Theme.KotlinSample">
         <activity
             android:name=".MainActivity"
             android:exported="true">

KotlinSample/app/src/main/java/com/example/kotlinsample/MainActivity.kt

@@ -1,10 +1,20 @@
 package com.example.kotlinsample
 
 import android.os.Bundle
+import android.util.Log
+import android.view.View
+import android.widget.TextView
 import androidx.activity.enableEdgeToEdge
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.view.ViewCompat
 import androidx.core.view.WindowInsetsCompat
+import com.example.kotlinsample.TrustedTimeClientAccessor.getTrustedTimeClientTask
+import com.google.android.gms.tasks.OnCompleteListener
+import com.google.android.gms.time.TrustedTimeClient
+import java.time.LocalDateTime
+import java.time.ZoneId
+import java.time.format.DateTimeFormatter
+
 
 class MainActivity : AppCompatActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -16,5 +26,56 @@ class MainActivity : AppCompatActivity() {
             v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom)
             insets
         }
+
+        // Use TrustedTimeClient anywhere in your app
+        findViewById<View>(R.id.button1).setOnClickListener(View.OnClickListener { v ->
+            // Retrieve the TrustedTimeClient from your application class
+            val myApp = applicationContext as MyApp
+
+            // In this example, System.currentTimeMillis() is used as a fallback if the
+            // client is null (i.e. client creation task failed) or when there is no time
+            // signal available. You may not want to do this if using the system clock is
+            // not suitable for your use case.
+            val currentTimeMillis = myApp.trustedTimeClient!!.computeCurrentUnixEpochMillis()
+            val instant = myApp.trustedTimeClient!!.computeCurrentInstant()
+            // trustedTimeClient.computeCurrentInstant() can be used if Instant is
+            // preferred to long for Unix epoch times and you are able to use the APIs.
+            val currentTime = LocalDateTime.ofInstant(instant, ZoneId.systemDefault())
+
+            val formattedString =
+                DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").format(currentTime)
+            Log.d("MainActivity", "currentTimeMillis: $currentTimeMillis")
+            Log.d("MainActivity", "formattedString: $formattedString")
+
+            findViewById<TextView>(R.id.textView1).text = "" + currentTimeMillis
+            findViewById<TextView>(R.id.textView2).text = formattedString
+        })
+
+        // Use in short-lived components like Activity
+        findViewById<View>(R.id.button2).setOnClickListener(View.OnClickListener { v ->
+            getTrustedTimeClientTask(this).addOnCompleteListener(OnCompleteListener { task ->
+                if (task.isSuccessful) {
+                    val trustedTimeClient: TrustedTimeClient = task.getResult()!!
+                    val currentTimeMillis = trustedTimeClient.computeCurrentUnixEpochMillis()
+                    val instant = trustedTimeClient.computeCurrentInstant()
+                    val currentTime = LocalDateTime.ofInstant(instant, ZoneId.systemDefault())
+
+                    val formattedString =
+                        DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").format(currentTime)
+                    Log.d("MainActivity", "currentTimeMillis: $currentTimeMillis")
+                    Log.d("MainActivity", "formattedString: $formattedString")
+
+                    findViewById<TextView>(R.id.textView1).text = "" + currentTimeMillis
+                    findViewById<TextView>(R.id.textView2).text = formattedString
+                } else {
+                    // Handle error
+                    // jp) エラーになるケースの具体例がわからないため、予期せぬ問題としてクラッシュさせる
+                    // en) Since I do not know the specific example of the case where an error occurs, I crash as an unexpected problem.
+                    val exception = task.exception
+                    Log.e("MainActivity", "error", exception)
+                    throw IllegalStateException("TrustedTimeClient is not available", exception)
+                }
+            })
+        })
     }
 }

KotlinSample/app/src/main/java/com/example/kotlinsample/MyApp.kt

@@ -0,0 +1,28 @@
+package com.example.kotlinsample
+
+import android.app.Application
+import android.util.Log
+import com.google.android.gms.tasks.OnCompleteListener
+import com.google.android.gms.time.TrustedTimeClient
+
+class MyApp : Application() {
+    var trustedTimeClient: TrustedTimeClient? = null
+
+    override fun onCreate() {
+        super.onCreate()
+
+        TrustedTimeClientAccessor.getTrustedTimeClientTask(this)
+            .addOnCompleteListener(OnCompleteListener { task ->
+                if (task.isSuccessful) {
+                    trustedTimeClient = task.getResult()
+                } else {
+                    // Handle error
+                    // jp) エラーになるケースの具体例がわからないため、予期せぬ問題としてクラッシュさせる
+                    // en) Since I do not know the specific example of the case where an error occurs, I crash as an unexpected problem.
+                    val exception = task.exception
+                    Log.e("MyApp", "error", exception)
+                    throw IllegalStateException("TrustedTimeClient is not available", exception)
+                }
+            })
+    }
+}

KotlinSample/app/src/main/java/com/example/kotlinsample/TrustedTimeClientAccessor.kt

@@ -0,0 +1,29 @@
+package com.example.kotlinsample
+
+import android.content.Context
+import com.google.android.gms.tasks.Task
+import com.google.android.gms.time.TrustedTime
+import com.google.android.gms.time.TrustedTimeClient
+import java.lang.reflect.Modifier.SYNCHRONIZED
+
+object TrustedTimeClientAccessor {
+    @Volatile
+    private var trustedTimeClientTask: Task<TrustedTimeClient>? = null
+
+    /**
+     * @see [Double-checked_locking](https://en.wikipedia.org/wiki/Double-checked_locking.Usage_in_Java)
+     * @see [Singleton_pattern](https://en.wikipedia.org/wiki/Singleton_pattern)
+     */
+    fun getTrustedTimeClientTask(context: Context): Task<TrustedTimeClient> {
+        if (trustedTimeClientTask != null) {
+            return trustedTimeClientTask!!
+        } else {
+            synchronized(TrustedTimeClientAccessor::class.java) {
+                if (trustedTimeClientTask == null) {
+                    trustedTimeClientTask = TrustedTime.createClient(context)
+                }
+                return trustedTimeClientTask!!
+            }
+        }
+    }
+}

KotlinSample/app/src/main/res/layout/activity_main.xml

@@ -1,19 +1,34 @@
 <?xml version="1.0" encoding="utf-8"?>
-<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:id="@+id/main"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
+    android:gravity="center"
+    android:orientation="vertical"
     tools:context=".MainActivity">
 
-    <TextView
+    <Button
+        android:id="@+id/button1"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:text="Hello World!"
-        app:layout_constraintBottom_toBottomOf="parent"
-        app:layout_constraintEnd_toEndOf="parent"
-        app:layout_constraintStart_toStartOf="parent"
-        app:layout_constraintTop_toTopOf="parent" />
+        android:text="test 1" />
+
+    <Button
+        android:id="@+id/button2"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="test 2" />
+
+    <TextView
+        android:id="@+id/textView1"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content" />
+
+    <TextView
+        android:id="@+id/textView2"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content" />
 
-</androidx.constraintlayout.widget.ConstraintLayout>
+</LinearLayout>