Upgrade android_splash_screen Gradle configuration (#2779)

I noticed that the `android_splash_screen` sample was outdated and was
not runnable due to gradle issues.

This commit fixes the Gradle setup for the `android_splash_screen`
sample.

Key changes include:
*   Upgrading Gradle wrapper from version 6.7 to 8.7.
* Migrating to the plugins block in `settings.gradle` and
`app/build.gradle` for applying Android, Kotlin, and Flutter Gradle
plugins.
* Removing the outdated `buildscript` block from the root
`build.gradle`.
*   Updating `compileSdkVersion` and `targetSdkVersion` to 34.
*   Setting `minSdkVersion` to `flutter.minSdkVersion`.
* Adding the `namespace` property as required by newer Android Gradle
Plugin versions.
*   Refactoring Kotlin constant declarations in `MainActivity.kt`.

@ericwindmill 

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).

Co-authored-by: Eric Windmill <eric@ericwindmill.com>

Author: NiazSagor

android_splash_screen/android/app/build.gradle

@@ -1,3 +1,10 @@
+plugins {
+    id "com.android.application"
+    id "kotlin-android"
+    // The Flutter Gradle Plugin must be applied after the Android and Kotlin Gradle plugins.
+    id "dev.flutter.flutter-gradle-plugin"
+}
+
 def localProperties = new Properties()
 def localPropertiesFile = rootProject.file('local.properties')
 if (localPropertiesFile.exists()) {
@@ -21,12 +28,9 @@ if (flutterVersionName == null) {
     flutterVersionName = '1.0'
 }
 
-apply plugin: 'com.android.application'
-apply plugin: 'kotlin-android'
-apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
-
 android {
-    compileSdkVersion 31
+    namespace "com.example.splash_screen_sample"
+    compileSdkVersion 34
 
     sourceSets {
         main.java.srcDirs += 'src/main/kotlin'
@@ -35,12 +39,21 @@ android {
     defaultConfig {
         // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
         applicationId "com.example.splash_screen_sample"
-        minSdkVersion 21
-        targetSdkVersion 30
+        minSdkVersion flutter.minSdkVersion
+        targetSdkVersion 34
         versionCode flutterVersionCode.toInteger()
         versionName flutterVersionName
     }
 
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_1_8
+        targetCompatibility = JavaVersion.VERSION_1_8
+    }
+
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_1_8
+    }
+
     buildTypes {
         release {
             // TODO: Add your own signing config for the release build.
@@ -55,7 +68,6 @@ flutter {
 }
 
 dependencies {
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
     implementation "androidx.core:core-splashscreen:1.0.0-alpha02"
     implementation "androidx.core:core:1.5.0-alpha05"
     implementation "androidx.core:core-ktx:1.6.0"

android_splash_screen/android/app/src/main/kotlin/com/example/splash_screen_sample/MainActivity.kt

@@ -203,9 +203,9 @@ class MainActivity : FlutterActivity() {
   }
 
   private companion object {
-    const val SPLASHSCREEN_ALPHA_ANIMATION_DURATION = 500 as Long
-    const val SPLASHSCREEN_TY_ANIMATION_DURATION = 500 as Long
-    const val SPLASHSCREEN_FINAL_ANIMATION_ALPHA_ANIMATION_DURATION = 250 as Long
-    const val WAIT_FOR_AVD_TO_FINISH = false
+      const val SPLASHSCREEN_ALPHA_ANIMATION_DURATION = 500L
+      const val SPLASHSCREEN_TY_ANIMATION_DURATION = 500L
+      const val SPLASHSCREEN_FINAL_ANIMATION_ALPHA_ANIMATION_DURATION = 250L
+      const val WAIT_FOR_AVD_TO_FINISH = false
   }
 }

android_splash_screen/android/build.gradle

@@ -1,29 +1,18 @@
-buildscript {
-    ext.kotlin_version = '1.5.31'
-    repositories {
-        google()
-        mavenCentral()
-    }
-
-    dependencies {
-        classpath 'com.android.tools.build:gradle:4.1.0'
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-    }
-}
-
 allprojects {
     repositories {
         google()
         mavenCentral()
     }
 }
 
-rootProject.buildDir = '../build'
+rootProject.buildDir = "../build"
 subprojects {
     project.buildDir = "${rootProject.buildDir}/${project.name}"
-    project.evaluationDependsOn(':app')
+}
+subprojects {
+    project.evaluationDependsOn(":app")
 }
 
-task clean(type: Delete) {
+tasks.register("clean", Delete) {
     delete rootProject.buildDir
 }

android_splash_screen/android/gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.7-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.7-all.zip

android_splash_screen/android/settings.gradle

@@ -1,11 +1,25 @@
-include ':app'
+pluginManagement {
+    def flutterSdkPath = {
+        def properties = new Properties()
+        file("local.properties").withInputStream { properties.load(it) }
+        def flutterSdkPath = properties.getProperty("flutter.sdk")
+        assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
+        return flutterSdkPath
+    }()
 
-def localPropertiesFile = new File(rootProject.projectDir, "local.properties")
-def properties = new Properties()
+    includeBuild("$flutterSdkPath/packages/flutter_tools/gradle")
 
-assert localPropertiesFile.exists()
-localPropertiesFile.withReader("UTF-8") { reader -> properties.load(reader) }
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
 
-def flutterSdkPath = properties.getProperty("flutter.sdk")
-assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
-apply from: "$flutterSdkPath/packages/flutter_tools/gradle/app_plugin_loader.gradle"
+plugins {
+    id "dev.flutter.flutter-plugin-loader" version "1.0.0"
+    id "com.android.application" version "8.6.0" apply false
+    id "org.jetbrains.kotlin.android" version "2.1.0" apply false
+}
+
+include ":app"