CODEWITHSUNDEEP
javaandroidandroid-recyclerview
Userlambda
Userlambda

Reputation: 85

Issue trying to use Recycler View

i'm trying to follow a tutorial for RecyclerView. But when i finish and try to test my code i got this message:

09-18 16:01:03.486 2521-2521/com.example.gon.recycleview E/AndroidRuntime: FATAL EXCEPTION: main
                                                                       Process: com.example.gon.recycleview, PID: 2521
                                                                       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.gon.recycleview/com.example.gon.recycleview.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                           at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:148)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                        Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
                                                                           at com.example.gon.recycleview.MainActivity.onCreate(MainActivity.java:22)
                                                                           at android.app.Activity.performCreate(Activity.java:6237)
                                                                           at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                           at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                           at android.os.Looper.loop(Looper.java:148) 
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                           at java.lang.reflect.Method.invoke(Native Method) 
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

I am a begginer and i don't understand this message. It seems that i have an error on this code with my setHasFixedSize() function

public class MainActivity extends Activity {

private RecyclerView mRecyclerView;
private RecyclerView.Adapter mAdapter;
private RecyclerView.LayoutManager mLayoutManager;
private String[] myDataset = {"Lundi", "Mardi", "Mercredi", "Vendredi", "Samedi", "Dimanche"};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.recycler_view);

    mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
    mRecyclerView.setHasFixedSize(true);
    mLayoutManager=new LinearLayoutManager(this);
    mRecyclerView.setLayoutManager(mLayoutManager);
    mAdapter=new RecyclerViewAdapter(myDataset);
    mRecyclerView.setAdapter(mAdapter);

}

}

can you help me please to understand what's wrong. my_recycler_view is my view which contain this :

<android.support.v7.widget.RecyclerView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android.id="@+id/my_recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

and I have an other view which describe lines of my list. And finally I have a class named RecyclerViewAdapter.

Upvotes: 0

Views: 54

Answers (1)

Ben P.
Ben P.

Reputation: 54194

In your XML layout, you have this line:

android.id="@+id/my_recycler_view"

change it to this instead:

android:id="@+id/my_recycler_view"

Because you've written android.id instead of android:id, the view isn't getting an id. Since it doesn't have an id, findViewById() can't find it, so it returns null (leading to your error).

Upvotes: 3

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