Flutter项目:app模块build.gradle空指针异常排查求助

报错信息 #

以调试模式启动lib\main.dart到sdk gphone64 x86 64...
执行Gradle任务'assembleDebug'...

FAILURE: 构建因异常失败。

• 位置：构建文件'C:\Users\mateu\StudioProjects\Coquinha\android\app\build.gradle'第66行

• 错误原因：评估:app项目时出现问题。

  java.lang.NullPointerException（无错误信息）

• 尝试方案：

  使用--stacktrace选项获取堆栈跟踪；
  使用--info或--debug选项获取更多日志输出；
  使用--scan选项获取完整分析信息。

• 更多帮助：https://help.gradle.org

构建耗时2s失败，异常：Gradle任务assembleDebug退出码为1

完整Build.Gradle代码 #

def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
    localPropertiesFile.withReader('UTF-8') { reader ->
        localProperties.load(reader)
    }
}

def flutterRoot = localProperties.getProperty('flutter.sdk')
if (flutterRoot == null) {
    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
}

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

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

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"

def keystoreProperties = new Properties()
def keystorePropertiesFile = rootProject.file('key.properties')
if (keystorePropertiesFile.exists()) {
    keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
}

android {
    compileSdkVersion flutter.compileSdkVersion
    ndkVersion flutter.ndkVersion

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

    kotlinOptions {
        jvmTarget = '1.8'
    }

    sourceSets {
        main.java.srcDirs += 'src/main/kotlin'
    }

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

    signingConfigs {
        release {
            keyAlias keystoreProperties['keyAlias']
            keyPassword keystoreProperties['keyPassword']
            storeFile keystoreProperties ['storeFile'] ? file(keystoreProperties[storeFile]) : null
            storePassword keystoreProperties['storePassword']
        }
    }

    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
            signingConfig signingConfigs.release
        }
    }
}

flutter {
    source '../..'
}

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
}

问题代码片段 #

signingConfigs {
    release {
        keyAlias keystoreProperties['keyAlias']
        keyPassword keystoreProperties['keyPassword']
        storeFile keystoreProperties ['storeFile'] ? file(keystoreProperties[storeFile]) : null
        storePassword keystoreProperties['storePassword']
    }
}

错误分析与修复 #

直接错误点 #

空指针异常由storeFile行的两处语法错误导致：

1. keystoreProperties ['storeFile']中键名前多了空格，导致Gradle无法正确解析属性访问，应改为keystoreProperties['storeFile']
2. file(keystoreProperties[storeFile])中storeFile未加引号，被Gradle当作变量而非字符串键，应改为keystoreProperties['storeFile']

修正后的代码片段 #

signingConfigs {
    release {
        keyAlias keystoreProperties['keyAlias']
        keyPassword keystoreProperties['keyPassword']
        storeFile keystoreProperties['storeFile'] ? file(keystoreProperties['storeFile']) : null
        storePassword keystoreProperties['storePassword']
    }
}

额外优化 #

若key.properties文件不存在，keystoreProperties中的所有属性都会是null，即使修复语法，调试模式下仍可能因release签名配置无效引发问题。建议将release签名配置逻辑包裹在文件存在判断中，确保调试时使用默认debug签名：

def keystoreProperties = new Properties()
def keystorePropertiesFile = rootProject.file('key.properties')
if (keystorePropertiesFile.exists()) {
    keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
}

android {
    // ... 其他配置保持不变 ...

    signingConfigs {
        release {
            if (keystorePropertiesFile.exists()) {
                keyAlias keystoreProperties['keyAlias']
                keyPassword keystoreProperties['keyPassword']
                storeFile file(keystoreProperties['storeFile'])
                storePassword keystoreProperties['storePassword']
            }
        }
    }

    buildTypes {
        release {
            signingConfig keystorePropertiesFile.exists() ? signingConfigs.release : signingConfigs.debug
        }
    }
}

内容的提问来源于stack exchange，提问作者Mateus Vitor