ListView and adapter

Question

I have created my own adapter for a ListView. Each row of the ListView is represented by two TextVews. I need to display some information in my ListView.

Here is my activity code:

public class MyCountriesActivity extends ListActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);    
        int row_ID = R.layout.list_item;
        ListAdapter adapt = new MyAdapter(this,row_ID); 
        setListAdapter(adapt);
        }
}

Here is my adapter code:

public class MyAdapter extends ArrayAdapter<String> {

    Activity a;
    int row_ID;
    String[] countries = { "USA", "France" };
    String[] years = { "1992", "2010" };

    public MyAdapter(Context context, int textViewResourceId) {
        super(context, textViewResourceId);
        a = (Activity) context;
        row_ID = textViewResourceId;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View row;
        if (convertView == null) { // Create new row view
            LayoutInflater inflater = a.getLayoutInflater();
            row = inflater.inflate(row_ID, parent, false);
        } else
            // reuse old row view to save time/battery
            row = convertView;

        /* Add new data to row object */
        TextView country = (TextView) row.findViewById(R.id.country);
        TextView year = (TextView) row.findViewById(R.id.year);
        country.setText(countries[position]);
        year.setText(years[position]);
        return row;
    }
}

But unfortunately this application crashes. What is wrong in my program?

Log:

03-04 17:41:11.044: E/AndroidRuntime(1277): FATAL EXCEPTION: main
03-04 17:41:11.044: E/AndroidRuntime(1277): java.lang.RuntimeException: Unable to start activity ComponentInfo{android.ledinov.namespace/android.ledinov.namespace.MyCountriesActivity}: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.os.Looper.loop(Looper.java:137)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.ActivityThread.main(ActivityThread.java:4424)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at java.lang.reflect.Method.invokeNative(Native Method)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at java.lang.reflect.Method.invoke(Method.java:511)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at dalvik.system.NativeStart.main(Native Method)
03-04 17:41:11.044: E/AndroidRuntime(1277): Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.ListActivity.onContentChanged(ListActivity.java:243)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:254)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.Activity.setContentView(Activity.java:1835)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.ledinov.namespace.MyCountriesActivity.onCreate(MyCountriesActivity.java:21)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.Activity.performCreate(Activity.java:4465)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
03-04 17:41:11.044: E/AndroidRuntime(1277):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
03-04 17:41:11.044: E/AndroidRuntime(1277):     ... 11 more

main.xml:

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

    <ListView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1" >
    </ListView>

</LinearLayout>

Answer 1

Try it this way

public class MyAdapter extends ArrayAdapter<String> {

    Activity a;
    int row_ID;
    String[] countries = { "USA", "France" };
    String[] years = { "1992", "2010" };

    public MyAdapter(Context context, int textViewResourceId) {
        super(context, textViewResourceId);
        this.context = context;
        row_ID = textViewResourceId;
    }



public View getView(int position, View convertView, ViewGroup parent) {

View row = convertView;

Holder ho = null;

if (row == null )
{

LayoutInflater inflater = ((Activity)context).getLayoutInflater();
row = inflater.inflate(row_ID, parent, false);

ho = new Holder();

txtCountry = (TextView) row.findViewById(R.id.country);
txtYear = (TextView) row.findViewById(R.id.year);

row.setTag(ho);


}

else{


  ho = (Holder)row.getTag();


}


txtCountry.setText(countries[position]);
txtYear.setText(years[position]);

return row;
}

static class Holder
    {
        TextView txtCountry;
        TextView txtYear;
    }

}

Answer 2

If I were to guess you either don't have a ListView element with the id @android:id/list in the R.layout.main layout file or the row layout file, R.layout.list_item, probably isn't composed from a single Textview element and the ArrayAdapter will crash with a ClassCastException in this case as it expects a single TextView element.

Also you might want to add to your adapter this method:

public void getCount() {
  return countries.length;
}

otherwise, even if your app will run, you would not see any elements in your ListView. If you have two TextViews in the R.layout.list_item this is wrong. Modify the adapter like this:

public MyAdapter(Context context, int textViewResourceId, int textId) {
        super(context, textViewResourceId, textId);
        a = (Activity) context;
        row_ID = textViewResourceId;
}

and where you instantiate the adapter:

int row_ID = R.layout.list_item;
int theId = R.id.the_id_of_one_of_the_textview_fromthelayout_above; (the id of the TextView from the R.layout.list_item)
ListAdapter adapt = new MyAdapter(this,row_ID, theId);