找不到recyclerview，那就再添加下面这句：
implementation'com.android.support:recyclerview-v7:28.0.0'
如果是其他的compileSdkVersion版本
//it requires compileSdkVersion 25
compile'com.android.support:recyclerview-v7:25.1.0
'compile'com.android.support:recyclerview-v7:25.0.0'
//it requires compileSdkVersion 24
compile'com.android.support:recyclerview-v7:24.1.1'
compile'com.android.support:recyclerview-v7:24.1.0'
//it requires compileSdkVersion 23
compile'com.android.support:recyclerview-v7:23.4.0'
compile'com.android.support:recyclerview-v7:23.3.0'
compile'com.android.support:recyclerview-v7:23.2.1'
compile'com.android.support:recyclerview-v7:23.2.0'
compile'com.android.support:recyclerview-v7:23.1.1'
compile'com.android.support:recyclerview-v7:23.1.0'
compile'com.android.support:recyclerview-v7:23.0.1'
compile'com.android.support:recyclerview-v7:23.0.0'
//it requires compileSdkVersion 22
compile'com.android.support:recyclerview-v7:22.2.1'
compile'com.android.support:recyclerview-v7:22.2.0'
compile'com.android.support:recyclerview-v7:22.1.1'
compile'com.android.support:recyclerview-v7:22.1.0'
compile'com.android.support:recyclerview-v7:22.0.0'
//it requires compileSdkVersion 21
compile'com.android.support:recyclerview-v7:21.0.3'
compile'com.android.support:recyclerview-v7:21.0.2'
compile'com.android.support:recyclerview-v7:21.0.0'
或者使用
compile'com.android.support:recyclerview-v7:+'
