Android使用SafeArgs实现导航时Gradle报错找不到nav_version属性如何解决?

你遇到的报错核心原因是：Gradle配置中多处使用了$nav_version变量，但根目录build.gradle的全局变量声明块中没有定义该变量，和Java/Kotlin混用无直接关联，此前移除Kotlin配置后仍报错就是因为没有解决变量未定义的核心问题。

1. 补充全局版本变量 #

在根目录build.gradle的buildscript下的ext块中声明nav_version变量，取值和你当前使用的导航组件版本保持一致即可。

2. 清理冗余Kotlin配置 #

因为你已不需要Kotlin相关配置，可同步移除所有Kotlin相关代码避免冗余：

• 根目录build.gradle移除Kotlin插件依赖、kotlin_version变量
• 模块级build.gradle移除Kotlin插件声明、kotlinOptions配置块、所有Kotlin专属依赖
• 全Java项目可更换SafeArgs插件为Java专属版本，直接生成Java类更适配

3. 同步Gradle配置 #

修改完成后同步项目即可解决报错。

根目录build.gradle #

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    ext {
        nav_version = "2.3.5"
    }
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath "com.android.tools.build:gradle:4.1.1"
        classpath "androidx.navigation:navigation-safe-args-gradle-plugin:$nav_version"

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

模块级build.gradle #

plugins {
    id 'com.android.application'
}

apply plugin: "androidx.navigation.safeargs.java"

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.nikhiljain.canvasdrawingsample"
        minSdkVersion 21
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"
        viewBinding {
            enabled = true
        }

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    implementation "androidx.navigation:navigation-fragment:$nav_version"
    implementation "androidx.navigation:navigation-ui:$nav_version"
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

内容的提问来源于stack exchange，提问作者VanessaF