UI-Elements of 2nd View arent referenceable by findViewById (NullReference)

Question

I am new to android-dev and experiencing the following problem:
All UI-Elements of the View list_excercises_item, which shows a ListView's item, are not referenceable by findViewById() only in the MainActivity-file.
I do already reference UI-Elements of the list_excercises_item in an own ArrayAdapter.

Context:
I want to fill my spinner with some data using an ArrayAdapter.

Exception:

java.lang.NullPointerException at example.trackfit.MainActivity.onCreate(MainActivity.java:28)

This instruction throws it: spinBodyCategory.setAdapter(arrayAdapter);
spinBodyCategory is null.

list_excercises_item.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal" android:layout_width="match_parent"
android:layout_height="wrap_content"
android:weightSum="1" android:layout_marginBottom="10px">

<EditText
    android:layout_width="0dp"
    android:layout_height="fill_parent"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:id="@+id/txt_excercise_name"
    android:hint="@string/hint_txt_excercise_name"
    android:layout_weight="0.4"
    android:inputType="text" />

<EditText
    android:layout_width="0dp"
    android:layout_height="fill_parent"
    android:inputType="numberDecimal"
    android:ems="10"
    android:id="@+id/txt_input_weight"
    android:paddingLeft="5px"
    android:layout_weight="0.20"
    android:hint="@string/hint_txt_input_weight" />

<Spinner
    android:layout_width="0dp"
    android:layout_height="fill_parent"
    android1:textAppearance="?android:attr/textAppearanceMedium"
    android:id="@+id/spin_body_category"
    android:hint="@string/hint_txt_excercise_name"
    android:gravity="right"
    android:layout_weight="0.40"
    android:inputType="text" />
</LinearLayout>

MainActivity.java:

package example.trackfit;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Spinner;
import java.util.ArrayList;
import example.trackfit.Models.Body;
import example.trackfit.Models.Excercise;

public class MainActivity extends AppCompatActivity {

private Spinner spinBodyCategory = null;

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

    Body[] bodies = Body.values();
    ArrayAdapter<Body> arrayAdapter = new ArrayAdapter<Body>(this, R.layout.list_excercises_item, bodies);
    ListView listView = (ListView)findViewById(R.id.list_excercises);
    spinBodyCategory = (Spinner)findViewById(R.id.spin_body_category);
    spinBodyCategory.setAdapter(arrayAdapter);
}

private void populateExcerciseList() {
    ArrayList<Excercise> excercises = Excercise.getExcercises();
    CustomExcerciseAdapter adapter = new CustomExcerciseAdapter(this, excercises);
    ListView listView = (ListView)findViewById(R.id.list_excercises);
    listView.setAdapter(adapter);
    }
}

CustomExcerciseAdapter.java:

package example.trackfit;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.EditText;

import java.util.ArrayList;

import example.trackfit.Models.Excercise;

public class CustomExcerciseAdapter extends ArrayAdapter<Excercise> {

    public CustomExcerciseAdapter(Context context, ArrayList<Excercise> excercises) {
        super(context, 0, excercises);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Excercise excercise = getItem(position);
        if (convertView == null)
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.list_excercises_item, parent, false);
        EditText txtExcerciseName = (EditText) convertView.findViewById(R.id.txt_excercise_name);
        EditText txtInputWeight = (EditText) convertView.findViewById(R.id.txt_input_weight);

        txtExcerciseName.setText(excercise.ExcerciseName);
        txtInputWeight.setText(Float.toString(excercise.Weight));

        return convertView;
    }
}

Edit:
This question is not a duplicate, I ofc know what a NullReferenceException is.
I did not know why this exception was thrown, since - I am new to android-dev and didnt know that I can only access childs of the View I set as my contentView.

Bill · Accepted Answer · 2016-07-21T15:20:40.297

Because findViewById is called from MainActivity.java, it is trying to find your spinner from the layout you set: activity_main.xml. Which is why you are getting a null pointer exception.

Since you have a spinner for each item on your list, you will have to set it from getView in your custom adapter.

Try copying and pasting

    Body[] bodies = Body.values();
    ArrayAdapter<Body> arrayAdapter = new ArrayAdapter<Body>(this, R.layout.list_excercises_item, bodies);
    spinBodyCategory = (Spinner)convertView.findViewById(R.id.spin_body_category);
    spinBodyCategory.setAdapter(arrayAdapter);

to your getView

UI-Elements of 2nd View arent referenceable by findViewById (NullReference)

1 Answers1