一、修改项目gradle.properties文件：

#true表示当前项目启用AndroidX
android.useAndroidX=false
#true表示将依赖包也迁移到AndroidX
android.enableJetifier=false

二、在build.gradle去掉androidx的引用，改为supportv7的引用

implementation 'com.android.support:appcompat-v7:28.0.0'

三、sync代码之后如果还有androidx包引用冲突的问题，可在build.gradle如下设置，完全去掉androidx的依赖：

android {
    configurations {
        all*.exclude group: 'androidx.arch.core'
        all*.exclude group: 'androidx.lifecycle'
        all*.exclude group: 'androidx.paging'
        all*.exclude group: 'androidx.room'
        all*.exclude group: 'androidx.sqlite'
        all*.exclude group: 'androidx.constraintlayout'
        all*.exclude group: 'androidx.vectordrawable'
        all*.exclude group: 'androidx.appcompat'
        all*.exclude group: 'androidx.asynclayoutinflater'
        all*.exclude group: 'androidx.cardview'
        all*.exclude group: 'androidx.car'
        all*.exclude group: 'androidx.collection'
        all*.exclude group: 'androidx.coordinatorlayout'
        all*.exclude group: 'androidx.cursoradapter'
        all*.exclude group: 'androidx.browser'
        all*.exclude group: 'androidx.customview'
        all*.exclude group: 'com.google.android.material'
        all*.exclude group: 'androidx.documentfile'
        all*.exclude group: 'androidx.drawerlayout'
        all*.exclude group: 'androidx.exifinterface'
        all*.exclude group: 'androidx.gridlayout'
        all*.exclude group: 'androidx.heifwriter'
        all*.exclude group: 'androidx.interpolator'
        all*.exclude group: 'androidx.leanback'
        all*.exclude group: 'androidx.loader'
        all*.exclude group: 'androidx.localbroadcastmanager'
        all*.exclude group: 'androidx.media2'
        all*.exclude group: 'androidx.mediarouter'
        all*.exclude group: 'androidx.multidex'
        all*.exclude group: 'androidx.palette'
        all*.exclude group: 'androidx.percentlayout'
        all*.exclude group: 'androidx.leanback'
        all*.exclude group: 'androidx.legacy'
        all*.exclude group: 'androidx.preference'
        all*.exclude group: 'androidx.print'
        all*.exclude group: 'androidx.recommendation'
        all*.exclude group: 'androidx.recyclerview'
        all*.exclude group: 'androidx.slice'
        all*.exclude group: 'androidx.slidingpanelayout'
        all*.exclude group: 'androidx.annotation'
        all*.exclude group: 'androidx.core'
        all*.exclude group: 'androidx.contentpager'
        all*.exclude group: 'androidx.legacy'
        all*.exclude group: 'androidx.dynamicanimation'
        all*.exclude group: 'androidx.emoji'
        all*.exclude group: 'androidx.fragment'
        all*.exclude group: 'androidx.media'
        all*.exclude group: 'androidx.tvprovider'
        all*.exclude group: 'androidx.vectordrawable'
        all*.exclude group: 'androidx.swiperefreshlayout'
        all*.exclude group: 'androidx.textclassifier'
        all*.exclude group: 'androidx.transition'
        all*.exclude group: 'androidx.versionedparcelable'
        all*.exclude group: 'androidx.viewpager'
        all*.exclude group: 'androidx.wear'
        all*.exclude group: 'androidx.webkit'
    }
}