Friday, August 31, 2018

java - NullPointerException when adding an object to ArrayList in Android




I'm trying to create a List View with BaseAdapter and i keep getting a Null Object Reference Error at the point of adding an object to an ArrayList.



Relevant code is below:



public class MainActivity extends ActionBarActivity {
int[] icons = {R.drawable.icon01, R.drawable.icon02, R.drawable.icon03, R.drawable.icon04, R.drawable.icon05, R.drawable.icon06, R.drawable.icon07, R.drawable.icon08, R.drawable.icon09, R.drawable.icon10, R.drawable.icon11, R.drawable.icon12};
ListView listView;

String[] title, desc;

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

listView = (ListView) findViewById(R.id.listView);

Resources resources = getResources();

title = resources.getStringArray(R.array.titles);
desc = resources.getStringArray(R.array.desc);

RT_Adapter rt_adapter = new RT_Adapter(this, title, desc, icons);
listView.setAdapter(rt_adapter);
}
}

class Creator {
String a, b;

int c;

Creator(String d, String e, int f) {
this.a = d;
this.b = e;
this.c = f;
Log.d("RT", a +" - "+b+" - "+c); //Position 01 - This is Description 01 - 2130837556
}
}


class RT_Adapter extends BaseAdapter {
Context c;
ArrayList list;

public RT_Adapter(Context context, String[] title, String[] descs, int[] icons) {
this.c = context;
for (int i = 0; i < title.length; i++) {
list.add(new Creator(title[i], descs[i], icons[i]));
}
}


...
}


I get the error at the below line(found out while debugging):



list.add(new Creator(title[i], descs[i], icons[i]));



Below is the actual Error in Logcat:



02-09 17:09:05.494      767-767/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.rt.droid.baseadapter01, PID: 767
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.rt.droid.baseadapter01/com.rt.droid.baseadapter01.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)

at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
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:898)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference
at com.rt.droid.baseadapter01.RT_Adapter.(MainActivity.java:71)
at com.rt.droid.baseadapter01.MainActivity.onCreate(MainActivity.java:36)
at android.app.Activity.performCreate(Activity.java:5933)

at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            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:898)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)


I don't Understand how i am getting a null object when i create the new Creator object to add to the ArrayList.



Any pointers would be greatly appreciated.


Answer



You never initialize ArrayList list;. So list.add(new Creator(title[i], descs[i], icons[i])); will throw a NPE.




Change:



ArrayList list;


to:



ArrayList list = new ArrayList();

No comments:

Post a Comment

plot explanation - Why did Peaches&#39; mom hang on the tree? - Movies &amp; TV

In the middle of the movie Ice Age: Continental Drift Peaches' mom asked Peaches to go to sleep. Then, she hung on the tree. This parti...