找不到viewModels，viewModels()

谷歌官方文档上学习mvvm，当我写到private val model: UserViewModel by viewModels()时，viewModels()爆红，查了资料，找到gradle，添加依赖

dependencies{
    implementation "androidx.activity:activity-ktx:1.2.0"//新添加
    implementation "androidx.fragment:fragment-ktx:1.3.0"
 
    implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.3.1'//我的文件已有的
    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.1'
 
}