无法同步或建立recyclerview

Question

我需要将recyclerview添加到我的项目中，但不会显示recyclerview的元素。

我的依赖项：

implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.google.firebase:firebase-database:11.8.0'
    implementation 'com.google.firebase:firebase-auth:11.8.0'
    implementation 'com.google.firebase:firebase-core:11.8.0'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation 'com.android.support:design:28.0.0'