MaterialRefreshLayout 不能实例化

[RedRiverCN]

3-10 03:02:02.220 6693-6693/com.example.myrecyclviewdemo E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.myrecyclviewdemo, PID: 6693 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myrecyclviewdemo/com.example.myrecyclviewdemo.MainActivity}: java.lang.RuntimeException: MaterialRefreshLayout can't be null at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) at android.app.ActivityThread.-wrap11(Unknown Source:0) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6494) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) Caused by: java.lang.RuntimeException: MaterialRefreshLayout can't be null