Sorry for bothering people so proficient, but I am new to Android and I am trying to learn...
Anyway, I am trying to build a Gallery with a custom adapter.
But I get NullPointerException as soon as the program tries to invoke the adapter.
Any help very much appreciated!!!!
public class MainActivity extends Activity {
private Gallery gal;
private List<Elementi> el;
@Override
protected void onCreate(Bundle savedInstanceState) {
List<Elementi> el = new ArrayList<Elementi>();
int[] tabDrawables = new int[] {
R.drawable.img1,R.drawable.img2,R.drawable.img3,R.drawable.img1,R.drawable.img4,R.drawable. img5,R.drawable.img6,R.drawable.img7,R.drawable.img8,R.drawable.img9,R.drawable.img10};
String[] descrizione = {"cani","boffo","gigo","belo","fyyfy","bogin","boginetti","zippe","ninne","cestino","cagnin o","cucciolo",};
for (int numero =1; numero <= 10;numero++) {
ImageView imgm = new ImageView(this);
imgm.setImageResource(tabDrawables[numero]);
el.add(new Elementi(imgm,descrizione[numero]));
};
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Gallery gal=(Gallery)findViewById(R.id.galleria);
gal.setAdapter(new MyAdapter());
}
public class MyAdapter extends ArrayAdapter<Elementi> {
public MyAdapter() {
super(MainActivity.this, R.layout.row, el);
}
public View getView(int position, View convertView,ViewGroup parent) {
View row= convertView;
TextView txt =(TextView)row.findViewById(R.id.testorow);
txt.setText(el.get(position).tx) ;
ImageView ima =(ImageView)row.findViewById(R.id.immagine);
ima.setImageResource(R.drawable.img1);
Toast.makeText(getApplicationContext(), Inte ger.toString(position), Toast.LENGTH_LONG).show();
return row;};
}
public class Elementi {
public ImageView im;
public String tx;
public Elementi(ImageView img,String txt){
ImageView im =img;
String tx = txt;
}
}
}
My LogCat:
11-29 20:26:28.327: E/AndroidRuntime(786): FATAL EXCEPTION: main
11-29 20:26:28.327: E/AndroidRuntime(786): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.gallery/com.example.gallery.MainActivity}: java.lang.NullPointerException
11-29 20:26:28.327: E/AndroidRuntime(786): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.os.Handler.dispatchMessage(Handler.java:99)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.os.Looper.loop(Looper.java:137)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.app.ActivityThread.main(ActivityThread.java:5039)
11-29 20:26:28.327: E/AndroidRuntime(786): at java.lang.reflect.Method.invokeNative(Native Method)
11-29 20:26:28.327: E/AndroidRuntime(786): at java.lang.reflect.Method.invoke(Method.java:511)
11-29 20:26:28.327: E/AndroidRuntime(786): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
11-29 20:26:28.327: E/AndroidRuntime(786): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
11-29 20:26:28.327: E/AndroidRuntime(786): at dalvik.system.NativeStart.main(Native Method)
11-29 20:26:28.327: E/AndroidRuntime(786): Caused by: java.lang.NullPointerException
11-29 20:26:28.327: E/AndroidRuntime(786): at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.widget.AbsSpinner.setAdapter(AbsSpinner.java:114)
11-29 20:26:28.327: E/AndroidRuntime(786): at com.example.gallery.MainActivity.onCreate(MainActivity.java:52)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.app.Activity.performCreate(Activity.java:5104)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
11-29 20:26:28.327: E/AndroidRuntime(786): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
11-29 20:26:28.327: E/AndroidRuntime(786): ... 11 more
11-29 20:26:28.547: D/dalvikvm(786): GC_CONCURRENT freed 387K, 17% free 2496K/3000K, paused 13ms+24ms, total 191ms
You need to check if(convertView == null) and when it is you need to inflate a new View, or you can let the super class handle this:
public View getView(int position, View convertView,ViewGroup parent) {
if(convertView == null)
convertView = super.getView(position, convertView, parent);
...
}
The presentations: Turbo Charge Your UI or World of ListView by lead Android programmers will help you understand how to work with getView() without slowing down your app.
Addition
From your LogCat:
Caused by: java.lang.NullPointerException
at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
This means the list you passed to the ArrayAdapter is null...
This is because you have two different copies of el:
private List<Elementi> el; // This one is null and is what's passed to your adapter
@Override
protected void onCreate(Bundle savedInstanceState) {
List<Elementi> el = new ArrayList<Elementi>(); // This one only exists in onCreate!
I don't really like how Java let's you do this without a warning... Simply change the last line to:
protected void onCreate(Bundle savedInstanceState) {
el = new ArrayList<Elementi>();
(However you will hit another NullPointerException if you don't address getView() as stated above.)