Question

I’m getting a NullPointerException in my Android app and, as far as I can tell from LogCat, it’s happening when trying to set a listview to clickable. This is my code.

public class MyActivity extends Activity {
private ListView lstView = (ListView) findViewById(R.id.listView1);
private SQLiteDatabase database;

private static final String fields[] = { "field1", "field2", "field3" };


/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {

    CursorAdapter dataSource;
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    //lstView.setClickable(true);   
private static final String fields[] = { "field1", "field2", "field3" };


/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    CursorAdapter dataSource;
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    lstView.setClickable(true);

    DatabaseHelper helper = new DatabaseHelper(this);
    database = helper.getWritableDatabase();
    Cursor data = database.query("mydb", fields, null, null, null, null, null);
    dataSource = new SimpleCursorAdapter(this, R.layout.row, data, fields, new int[] {R.id.field1, R.id.field2});
    database.close();
    lstView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

          @Override
          public void onItemClick(AdapterView<?> arg0, View arg1, int position, long arg3) {
            Intent newActivity = new Intent(getApplicationContext(), NewIntent.class);
            newActivity.putExtra("itemId",lstView.getItemIdAtPosition(position));
            // start activity
            startActivity(newActivity);
          }
        });

}


}

This is the LogCat output

01-10 14:03:53.740: E/AndroidRuntime(30361): FATAL EXCEPTION: main
01-10 14:03:53.740: E/AndroidRuntime(30361): java.lang.RuntimeException: Unable to start activity ComponentInfo{app.jonward.myapp/app.jonward.myapp.MyActivity}: java.lang.NullPointerException
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1821)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1842)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.app.ActivityThread.access$1500(ActivityThread.java:132)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1038)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.os.Looper.loop(Looper.java:150)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.app.ActivityThread.main(ActivityThread.java:4263)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at java.lang.reflect.Method.invokeNative(Native Method)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at java.lang.reflect.Method.invoke(Method.java:507)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at dalvik.system.NativeStart.main(Native Method)
01-10 14:03:53.740: E/AndroidRuntime(30361): Caused by: java.lang.NullPointerException
01-10 14:03:53.740: E/AndroidRuntime(30361):    at  app.jonward.castr.CastrActivity.onCreate(MyActivity.java:31)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1072)
01-10 14:03:53.740: E/AndroidRuntime(30361):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1785)
01-10 14:03:53.740: E/AndroidRuntime(30361):    ... 11 more

The code on line 31 of MyActivity that LogCat says caused the exception is

lstView.setClickable(true);

FIXED
Here is the working code. There are a few changes.
public class MyActivity extends ListActivity {
private SQLiteDatabase database;
private static final String fields[] = { “field1”, “field2”, “_id” };

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {

    CursorAdapter dataSource;
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    DatabaseHelper helper = new DatabaseHelper(this);
    database = helper.getWritableDatabase();
    Cursor data = database.query("castr", fields, null, null, null, null, null);
    dataSource = new SimpleCursorAdapter(this, R.layout.row, data, fields, new int[] {R.id.field1, R.id.field2});
    final ListView view = getListView();

    view.setHeaderDividersEnabled(true);
    view.addHeaderView(getLayoutInflater().inflate(R.layout.row, null));

    database.close();

    view.setOnItemClickListener(new AdapterView.OnItemClickListener() {

          @Override
          public void onItemClick(AdapterView<?> arg0, View arg1, int position, long arg3) {

            // Prepare intent
            Intent newActivity = new Intent(getApplicationContext(), NewActivity.class);
            newActivity.putExtra("itemId",view.getItemIdAtPosition(position));
            // start activity
            startActivity(newActivity);
          }
        });

}
}

Answer 1

you should get the listView reference from the layout. probably use something like this..

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

and then set listView to clickable.

on the other hand, why do you want to set a list view to be clickable?, you need not do it, list items are clickable by default.