有一个用Kotlin做的非常简单的app，在Android Studio 3.0下可以很好的运行在Android 8.0，Android 6.0和Android 5.1

但是当我在 Android 下运行应用程序时，我收到错误消息“java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{info.dodata.mirror/ui.UIMain}: java.lang.ClassNotFoundException: ui.UIMain” 4.1. 2(这是一部真正的手机)和Android 4.2.2

您可以通过在 https://www.dropbox.com/s/9f0yxp5pqqxtcxq/Mirror.zip?dl=0 下载应用程序来测试它

UIMain.kt

package ui
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import info.dodata.mirror.R
class UIMain : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.layout_main)
    }

}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="info.dodata.mirror">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <activity android:name="ui.UIMain">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

build.gradle(模块:应用程序)

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 26
    flavorDimensions "default"

    defaultConfig {

        // Enabling multidex support.
        multiDexEnabled true

        applicationId "info.dodata.mirror"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 1
        versionName "1.01"
        archivesBaseName = "BackupSettings-V" + versionName
    }

    productFlavors {
        free {
            applicationId "info.dodata.mirror"
        }

        pro {
            applicationId "info.dodata.mirror.pro"
        }
    }


    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            buildConfigField "boolean", "IsDebugMode", "false"
        }

        debug {
            buildConfigField "boolean", "IsDebugMode", "true"
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:multidex:1.0.2'
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:26.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'
    implementation "org.jetbrains.anko:anko-commons:$anko_version"
    implementation "org.jetbrains.anko:anko-sqlite:$anko_version"
}

build.gradle(上)

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    ext.kotlin_version = '1.1.51'
    ext.anko_version = '0.10.2'

    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_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
}

最佳答案

在 Android 5.0 及更高版本上，ART 会自动一起加载多个 .dex 文件。然而，在早期的 Android 版本中，Dalvik 仅使用主要的 classes.dex 启动应用程序，并且应用程序必须在完成任何其他操作之前加载次要的 .dex 文件。

这由 multidex 支持库处理，但您没有遵循 instructions .这意味着当系统尝试启动您的 Activity 时，您的某些类不存在，从而导致崩溃。

Depending on whether you override the Application class, perform one of the following:

• If you do not override the Application class, edit your manifest file to set android:name in the <application> tag as follows:

  <?xml version="1.0" encoding="utf-8"?>
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.example.myapp">
      <application
              android:name="android.support.multidex.MultiDexApplication" >
          ...
      </application>
  </manifest>
  

• If you do override the Application class, change it to extend MultiDexApplication (if possible) as follows:

  public class MyApplication extends MultiDexApplication { ... }
  

• Or if you do override the Application class but it's not possible to change the base class, then you can instead override the attachBaseContext() method and call MultiDex.install(this) to enable multidex:

  public class MyApplication extends SomeOtherApplication {
    @Override
    protected void attachBaseContext(Context base) {
       super.attachBaseContext(base);
       MultiDex.install(this);
    }
  }
  

您目前没有覆盖 Application , 所以你应该遵循第一种情况。

关于android - 为什么该应用程序不能在 Kotlin 的 Android 4.x 下运行？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47214941/