Flutter使用url_launcher插件时出现D8空指针编译错误

我在Flutter项目中使用url_launcher插件时遇到构建错误。为保证版本兼容性，我在pubspec.yml中将依赖版本设为any：

dependencies:
  url_launcher: any

在Android目录下执行./gradlew clean build时Gradle构建成功，但在Android模拟器上运行Flutter项目时失败，控制台报错如下：

ERROR:D:\Workspace\Projects\trip\build\url_launcher_android\intermediates\runtime_library_classes_jar\debug\classes.jar: D8: java.lang.NullPointerException

FAILURE: Build failed with an exception.

* 出错原因：
任务':app:mergeLibDexDebug'执行失败。
> 无法解析配置':app:debugRuntimeClasspath'的所有文件。
   > 转换classes.jar（项目:url_launcher_android）失败...
      > DexingWithClasspathTransform执行失败: ...\classes.jar.
         > 转换dex文件时出错。

* 尝试方案：（Gradle故障排除步骤）
...
BUILD FAILED in 1s
Error: Gradle task assembleDebug failed with exit code 1

• Flutter 3.22.0
• Gradle 8.2.1
• Android SDK 35

• 在Android目录下执行./gradlew clean build构建成功，但运行Flutter项目时失败
• D8 dex转换阶段出现NullPointerException
• 错误仅发生在url_launcher_android模块

相关配置文件内容 #

android/build.gradle #

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

rootProject.buildDir = "../build"
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(":app")
}

tasks.register("clean", Delete) {
    delete rootProject.buildDir
}

android/app/build.gradle #

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()) {
    localPropertiesFile.withReader("UTF-8") { reader ->
        localProperties.load(reader)
    }
}

def flutterVersionCode = localProperties.getProperty("flutter.versionCode")
if (flutterVersionCode == null) {
    flutterVersionCode = "1"
}

def flutterVersionName = localProperties.getProperty("flutter.versionName")
if (flutterVersionName == null) {
    flutterVersionName = "1.0"
}

android {
    namespace = "com.example.trip"
    compileSdk = flutter.compileSdkVersion
    ndkVersion = flutter.ndkVersion

    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }

    defaultConfig {
        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
        applicationId = "com.example.trip"
        // You can update the following values to match your application needs.
        // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-gradle-build-configuration.
        minSdk = flutter.minSdkVersion
        targetSdk = flutter.targetSdkVersion
        versionCode = flutterVersionCode.toInteger()
        versionName = flutterVersionName
    }

    buildTypes {
        release {
            // TODO: Add your own signing config for the release build.
            // Signing with the debug keys for now, so `flutter run --release` works.
            signingConfig = signingConfigs.debug
        }
    }
}

flutter {
    source = "../.."
}

gradle-wrapper.properties #

distributionBase=GRADLE_USER_HOME
distributionPath=wrapper/dists
zipStoreBase=GRADLE_USER_HOME
zipStorePath=wrapper/dists
distributionUrl=https\://services.gradle.org/distributions/gradle-8.2.1-all.zip

1. 锁定url_launcher兼容版本
   使用any会拉取最新版本，可能与当前Flutter/Gradle版本不兼容。修改pubspec.yml指定兼容版本：

   dependencies:
     url_launcher: ^6.2.5
   

   执行flutter pub get更新依赖。

2. 调整Gradle编译选项
   在android/app/build.gradle的android块中添加D8配置，避免空指针：

   android {
       // ... 原有代码
       dexOptions {
           javaMaxHeapSize "4g"
           preDexLibraries = false
       }
       // ... 原有代码
   }
   

3. 修复构建目录配置冲突
   现有构建目录配置可能与Flutter构建流程冲突，注释或移除android/build.gradle中以下代码：

   // rootProject.buildDir = "../build"
   // subprojects {
   //     project.buildDir = "${rootProject.buildDir}/${project.name}"
   // }
   

4. 彻底清理并重新构建
   执行以下命令清除缓存后重新构建：

   flutter clean
   rm -rf android/.gradle
   rm -rf ~/.gradle/caches
   flutter pub get
   flutter run
   

内容的提问来源于stack exchange，提问作者Mingtiao Shiqi