Using platform specific standard formatters

README.md

@@ -11,4 +11,24 @@ This is a Kotlin Multiplatform project targeting Android, iOS, Desktop.
   you need this entry point for your iOS app. This is also where you should add SwiftUI code for your project.
 
 
-Learn more about [Kotlin Multiplatform](https://www.jetbrains.com/help/kotlin-multiplatform-dev/get-started.html)…
+Learn more about [Kotlin Multiplatform](https://www.jetbrains.com/help/kotlin-multiplatform-dev/get-started.html)…
+
+## Recommendation
+
+Why you should use standard formatters, because every locale uses different style for date/time, like spacing, 12/24 format, etc...
+
+This result is from same code with different locales (US, DE, FR, CS):
+
+US: uses 12h format, `MM dd, yyyy`, comma and space as date separator.
+![US](./imgs/image_us.png)
+
+DE: uses 24h format, `dd.MM.yyyy`, dot as date separator.
+![DE](./imgs/image_de.png)
+
+FR: uses 24h format, `dd MMM yyyy`, space separator for date.
+![FR](./imgs/image_fr.png)
+
+CS: uses 24h format, `dd. MM. yyyy`, dot and space as date separator.
+![CS](./imgs/image_cs.png)
+
+Please respect regional settings and use standard formatters if you return output for users :).

composeApp/build.gradle.kts

@@ -81,12 +81,16 @@ android {
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_11
         targetCompatibility = JavaVersion.VERSION_11
+
+        isCoreLibraryDesugaringEnabled = true
     }
     buildFeatures {
         compose = true
     }
     dependencies {
         debugImplementation(compose.uiTooling)
+
+        coreLibraryDesugaring(libs.desugar.jdk.libs)
     }
 }
 

composeApp/src/androidMain/kotlin/DateTimeAdapter.android.kt

@@ -0,0 +1,30 @@
+import kotlinx.datetime.*
+import java.time.format.DateTimeFormatter
+import java.time.format.FormatStyle
+
+/**
+ * You should use standard date and time formatting patterns for the platform you are targeting.
+ * The reason is that every Locale uses different patterns for formatting dates and times.
+ * Standard FormatStyle.[SHORT|MEDIUM|LONG] solve this problem for you.
+ * For example 12/24-hour format, dividers, order of day/month/year in output, etc...
+ *
+ * Try to change Locale of your system from US/FR/DE and see how the output changes.
+ *
+ * We can create our domain FormatStyle of course and propagate expected format from common
+ * module and not use only MEDIUM format here...
+ */
+actual fun getDateTimeAdapter(): DateTimeAdapter = object : DateTimeAdapter {
+    override fun formatLocalDateTime(dateTime: LocalDateTime): String {
+        return dateTime.toJavaLocalDateTime().format(
+            DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM, FormatStyle.MEDIUM)
+        )
+    }
+
+    override fun formatLocalTime(time: LocalTime): String = time.toJavaLocalTime().format(
+        DateTimeFormatter.ofLocalizedTime(FormatStyle.MEDIUM)
+    )
+
+    override fun formatLocalDate(date: LocalDate): String = date.toJavaLocalDate().format(
+        DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM)
+    )
+}

composeApp/src/commonMain/kotlin/App.kt

@@ -22,16 +22,10 @@ import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import kotlinx.coroutines.delay
 import kotlinx.datetime.Clock
-import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.UtcOffset
-import kotlinx.datetime.format
-import kotlinx.datetime.format.char
-import kotlinx.datetime.toInstant
 import kotlinx.datetime.toLocalDateTime
 import org.jetbrains.compose.ui.tooling.preview.Preview
-import kotlin.time.Duration.Companion.hours
 
 data class City(
     val name: String,
@@ -58,7 +52,7 @@ fun App() {
             )
         }
         LaunchedEffect(true) {
-            while(true) {
+            while (true) {
                 cityTimes = cities.map {
                     val now = Clock.System.now()
                     it to now.toLocalDateTime(it.timeZone)
@@ -87,31 +81,12 @@ fun App() {
                         horizontalAlignment = Alignment.End
                     ) {
                         Text(
-                            text = dateTime
-                                .format(
-                                    LocalDateTime.Format {
-                                        hour()
-                                        char(':')
-                                        minute()
-                                        char(':')
-                                        second()
-                                    }
-                                ),
+                            text = getDateTimeAdapter().formatLocalTime(dateTime.time),
                             fontSize = 30.sp,
                             fontWeight = FontWeight.Light
                         )
                         Text(
-                            text = dateTime
-                                .format(
-                                    LocalDateTime.Format {
-                                        dayOfMonth()
-                                        char('/')
-                                        monthNumber()
-                                        char('/')
-                                        year()
-                                    }
-                                ),
-                            fontSize = 16.sp,
+                            text = getDateTimeAdapter().formatLocalDate(dateTime.date),
                             fontWeight = FontWeight.Light,
                             textAlign = TextAlign.End
                         )

composeApp/src/commonMain/kotlin/DateTimeAdapter.kt

@@ -0,0 +1,11 @@
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.LocalDateTime
+import kotlinx.datetime.LocalTime
+
+interface DateTimeAdapter {
+    fun formatLocalDateTime(dateTime: LocalDateTime): String
+    fun formatLocalTime(time: LocalTime): String
+    fun formatLocalDate(date: LocalDate): String
+}
+
+expect fun getDateTimeAdapter(): DateTimeAdapter

composeApp/src/desktopMain/kotlin/DateTimeAdapter.desktop.kt

@@ -0,0 +1,17 @@
+import kotlinx.datetime.*
+import java.time.format.DateTimeFormatter
+import java.time.format.FormatStyle
+
+actual fun getDateTimeAdapter(): DateTimeAdapter = object : DateTimeAdapter {
+    override fun formatLocalDateTime(dateTime: LocalDateTime): String = dateTime.toJavaLocalDateTime().format(
+        DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM, FormatStyle.MEDIUM)
+    )
+
+    override fun formatLocalTime(time: LocalTime): String = time.toJavaLocalTime().format(
+        DateTimeFormatter.ofLocalizedTime(FormatStyle.MEDIUM)
+    )
+
+    override fun formatLocalDate(date: LocalDate): String = date.toJavaLocalDate().format(
+        DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM)
+    )
+}

composeApp/src/iosMain/kotlin/DateTimeAdapter.ios.kt

@@ -0,0 +1,20 @@
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.LocalDateTime
+import kotlinx.datetime.LocalTime
+
+/**
+ * Use iOS DateFormatter: https://stackoverflow.com/a/41769435/4024146"
+ */
+actual fun getDateTimeAdapter(): DateTimeAdapter = object : DateTimeAdapter {
+    override fun formatLocalDateTime(dateTime: LocalDateTime): String {
+        TODO("Not yet implemented")
+    }
+
+    override fun formatLocalTime(time: LocalTime): String {
+        TODO("Not yet implemented")
+    }
+
+    override fun formatLocalDate(date: LocalDate): String {
+        TODO("Not yet implemented")
+    }
+}

gradle/libs.versions.toml

@@ -11,6 +11,7 @@ androidx-espresso-core = "3.6.1"
 androidx-material = "1.12.0"
 androidx-test-junit = "1.2.1"
 compose-plugin = "1.6.11"
+desugar_jdk_libs = "2.0.4"
 junit = "4.13.2"
 kotlin = "2.0.0"
 datetime = "0.6.0"
@@ -28,6 +29,9 @@ androidx-constraintlayout = { group = "androidx.constraintlayout", name = "const
 androidx-activity-compose = { module = "androidx.activity:activity-compose", version.ref = "androidx-activityCompose" }
 kotlinx-datetime = { module = "org.jetbrains.kotlinx:kotlinx-datetime", version.ref = "datetime"}
 
+# Desugar for support Java Time API on older Android versions
+desugar_jdk_libs = { module = "com.android.tools:desugar_jdk_libs", version.ref = "desugar_jdk_libs" }
+
 [plugins]
 androidApplication = { id = "com.android.application", version.ref = "agp" }
 androidLibrary = { id = "com.android.library", version.ref = "agp" }