android java onClick Could not execute method of the activity

Question

This is my first time working with the recyclerview and I am getting some errors about android:onClick="addItem" here is what I get when I try to add a line of text to my recyclerview. I usually use my phone to test my apps.

java.lang.IllegalStateException: Could not execute method of the activity
            at android.view.View$1.onClick(View.java:4012)
            at android.view.View.performClick(View.java:4761)
            at android.view.View$PerformClick.run(View.java:19767)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5312)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
     Caused by: java.lang.reflect.InvocationTargetException
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at android.view.View$1.onClick(View.java:4007)
????????????at android.view.View.performClick(View.java:4761)
????????????at android.view.View$PerformClick.run(View.java:19767)
????????????at android.os.Handler.handleCallback(Handler.java:739)
????????????at android.os.Handler.dispatchMessage(Handler.java:95)
????????????at android.os.Looper.loop(Looper.java:135)
????????????at android.app.ActivityThread.main(ActivityThread.java:5312)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
????????????at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
            at com.sapps.app.testapp2.MainActivity.addItem(MainActivity.java:53)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at android.view.View$1.onClick(View.java:4007)
????????????at android.view.View.performClick(View.java:4761)
????????????at android.view.View$PerformClick.run(View.java:19767)
????????????at android.os.Handler.handleCallback(Handler.java:739)
????????????at android.os.Handler.dispatchMessage(Handler.java:95)
????????????at android.os.Looper.loop(Looper.java:135)
????????????at android.app.ActivityThread.main(ActivityThread.java:5312)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
????????????at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)

Here is my code where I think is the error, but I don't know exactly:

 public class MainActivity extends ActionBarActivity {

private EditText mText;
private RecyclerView.LayoutManager mLayoutManager;
private RecyclerView recyclerView;
private Button btn;
private CustomRecyclerAdapter mAdapter;

private List<Data> mData = new ArrayList<>();

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

    // Initializing views.
    mText = (EditText) findViewById(R.id.textEt);
    recyclerView = (RecyclerView) findViewById(R.id.recycler);

    // If the size of views will not change as the data changes.
    recyclerView.setHasFixedSize(true);

    // Setting the LayoutManager.
    mLayoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(mLayoutManager);

    // Setting the adapter.
    CustomRecyclerAdapter mAdapter = new CustomRecyclerAdapter();
    recyclerView.setAdapter(mAdapter);
}



// Called when add button is clicked.
public void addItem(View v) {

    if(mText!=null) {
        Data dataToAdd = new Data(mText.getText().toString()); mData.add(dataToAdd);
    }
}

}

And here is my recyclerview adapter to know for sure:

public class CustomRecyclerAdapter extends RecyclerView.Adapter<RecyclerViewHolder> {

    CustomRecyclerAdapter mAdapter;

    private List<Data> mData = Collections.emptyList();

    public CustomRecyclerAdapter() {
        // Pass context or other static stuff that will be needed.
    }

    public void updateList(List<Data> data) {
        mData = data;
        notifyDataSetChanged();
    }
    @Override
    public int getItemCount() {
        return mData.size();
    }

    @Override
    public RecyclerViewHolder onCreateViewHolder(ViewGroup viewGroup, int position) {
        LayoutInflater inflater = LayoutInflater.from(viewGroup.getContext());
        View itemView = inflater.inflate(R.layout.list_item, viewGroup, false);
        return new RecyclerViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(RecyclerViewHolder viewHolder, int position) {
        viewHolder.title.setText(mData.get(position).text);
    }

    public void addItemInRec(int position, Data data) {
        mData.add(data);
        notifyItemInserted(position);
    }

    public void removeItem(int position) {
        mData.remove(position);
        notifyItemRemoved(position);
    }
}

My MainActivity xml file:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <EditText
            android:id="@+id/textEt"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="Text"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Add"
            android:onClick="addItem"/>

    </LinearLayout>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="vertical"/>

</LinearLayout>

Maybe it is my ViewHolder:

public class RecyclerViewHolder extends RecyclerView.ViewHolder {

    public TextView title;

    public RecyclerViewHolder(View itemView) {
        super(itemView);
        title = (TextView) itemView.findViewById(R.id.title);
    }
}

Or Data.java class:

public class Data {

        public String text;
        public Data(String text) {
            this.text = text;
        }
    }

Answer 1

The key is in your error message:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
            at com.sapps.app.testapp2.MainActivity.addItem(MainActivity.java:53)

A good tip for learning from your error output is to look at each "Caused by" statement, and scan through the log until you find one of your own files referenced. Then that part of the error log will even tell you what line your code was failing on ( in this case it is line 53 on MainActivity.java).

A Null Pointer Exception in Java is when you attempt to call a method on some object 'A', but that object 'A' is currently null.

So this error message means: "On line 53 of MainActivity.java, you tried to call a method on some object which doesn't exist yet, so I crashed."

The method that is failing is EditText mText = (EditText) findViewById(R.id.textEt);

Usually this type of failure means that you aren't finding the right ID from your layout. Double check that textEt is the correct ID for this layout element.

EDIT:

Still not sure why your views aren't getting populated, but I did notice an error with your adapter. You are redefining mAdapter, so you have 2 copies, one in local scope and one as a member to MainActivity. This will definitely mess things up.

Right here:

// Setting the adapter.
CustomRecyclerAdapter mAdapter = new CustomRecyclerAdapter();
recyclerView.setAdapter(mAdapter)

You are redefining mAdapter locally. Do this instead:

// Setting the adapter.
mAdapter = new CustomRecyclerAdapter();
recyclerView.setAdapter(mAdapter)