CODEWITHSUNDEEP
androidandroid-intentandroid-listview
Bernice
Bernice

Reputation: 2592

Intent for generated listview app stopped working

I am trying to run an android application where I have a MainActivity which consists of a generated ListView of TextView items and an Intent so that when the user clicks on the first item in the list view, he goes to a second activity named PortalActivity. This is what I have tried to do so far. When I try to run it in eclipse android emulator, it shows this popup that 'Unfortunately, myApp stopped working'.

public class MainActivity extends ListActivity
{
    final String[] menuItems = {"Portal", "Settings", "Help", "About"};

    @Override
    protected void onCreate (Bundle savedInstanceState)
    {
         super.onCreate(savedInstanceState);
         setListAdapter(new ArrayAdapter<String>(MainActivity.this, R.layout.listview_item, R.id.listview_tv, menuItems));

         ListView yourListView = (ListView) findViewById(R.id.listview_tv);
         yourListView.setOnItemClickListener(new OnItemClickListener() 
         {
              @Override
              public void onItemClick(AdapterView<?> parent, View view, int position, long id)    {
                  if (position == 0)
                  {
                    Intent myIntent = new Intent(MainActivity.this,PortalActivity.class);
                    startActivity(myIntent);
                  }
              }
         });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}

listview_item.xml: (layout for Main Activity)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView 
        android:id="@+id/listview_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#000000"
        android:text="TextView"  
    />

</LinearLayout>

and PortalActivity is just an activity with another defined layout. I'm sure the problem is around the intent since when commenting it, the app runs and shows the list view and the layout for portal activity is also working fine.

This is the StackTrace in Log Cat

11-06 13:05:35.167: E/AndroidRuntime(1590): FATAL EXCEPTION: main
11-06 13:05:35.167: E/AndroidRuntime(1590): Process: com.example.androidexample, PID: 1590
11-06 13:05:35.167: E/AndroidRuntime(1590): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.androidexample/com.example.androidexample.MainActivity}: java.lang.NullPointerException
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.app.ActivityThread.access$700(ActivityThread.java:135)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.os.Handler.dispatchMessage(Handler.java:102)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.os.Looper.loop(Looper.java:137)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.app.ActivityThread.main(ActivityThread.java:4998)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at java.lang.reflect.Method.invokeNative(Native Method)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at java.lang.reflect.Method.invoke(Method.java:515)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at dalvik.system.NativeStart.main(Native Method)
11-06 13:05:35.167: E/AndroidRuntime(1590): Caused by: java.lang.NullPointerException
11-06 13:05:35.167: E/AndroidRuntime(1590):     at com.example.androidexample.MainActivity.onCreate(MainActivity.java:25)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.app.Activity.performCreate(Activity.java:5243)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-06 13:05:35.167: E/AndroidRuntime(1590):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
11-06 13:05:35.167: E/AndroidRuntime(1590):     ... 11 more

Does someone have any idea what is wrong please? I am very new to Android so thanks for any help :)

Upvotes: 1

Views: 526

Answers (1)

David Wasser
David Wasser

Reputation: 95646

This call

     ListView yourListView = (ListView) findViewById(R.id.listview_tv);

returns null because there is no ListView in the layout with the resource ID R.id.listview_tv. Then the following line

     yourListView.setOnItemClickListener(new OnItemClickListener()

gets a NullPointerException because yourListView is null.

Since you are extending ListActivity, to get the ListView widget you need to call getListView() like this:

ListView yourListView = getListView();

Upvotes: 1

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