报错如下：
Caused by: com.android.build.gradle.internal.crash.ExternalApiUsageException: groovy.lang.GroovyRuntimeException: Cannot set the value of read-only property 'outputFile' for ApkVariantOutputImpl_Decorated{apkData=Main{type=MAIN, fullName=xiaomiDebug, filters=[], versionCode=1, versionName=1.0}} of type com.android.build.gradle.internal.api.ApkVariantOutputImpl.

报错截图：

error.png

大家可以注意看一下，AS升级到3.0以上版本后，截图上的红框处的代码都要改动，否则是无法正常打包的。那要改成什么样呢，如下图所示：

success.png

代码如下：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.3"

    defaultConfig {
        applicationId "com.sprsoft.history"
        minSdkVersion 21
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        flavorDimensions "default"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
        applicationVariants.all { variant ->
            variant.outputs.all { output ->
                def outputFile = output.outputFile
                def fileName
                if (outputFile != null && outputFile.name.endsWith('.apk')) {
                    if (variant.buildType.name.equals('release')) {//如果是release包
                        fileName = "cbx_release_v${defaultConfig.versionName}.apk"
                    } else if (variant.buildType.name.equals('debug')) {//如果是debug包
                        fileName = "cbx_debug_v${defaultConfig.versionName}.apk"
                    }
                    outputFileName = fileName
                }
            }
        }
    }
    productFlavors {
        wangdoujia {}
        xiaomi {}
        yingyongbao {}
    }
    productFlavors.all {
        flavor -> flavor.manifestPlaceholders = [UMENG_CHANNEL: name]
    }

    lintOptions {
        checkReleaseBuilds false
        abortOnError false
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])

    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

补充：
还需要在AndroidManifest.xml文件中添加：“<meta-data />”标签代码

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <meta-data
            android:name="UMENG_CHANNEL"
            android:value="${UMENG_CHANNEL}" />
    </application>

</manifest>