listview does not display

Question

im making project with a custom listview. When i run the project i just get a blank activity. I wrote the BaseAdapter class to put the data in the listview. I pass a String ArrayList to the baseadapter to fill the listview. Any help? Thanks

  public class MainActivity extends Activity {

  ListView L;
 ArrayList<String> data= new ArrayList<String>();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    data.add("two");
    data.add("Three");
    data.add("Four");
    L=(ListView) findViewById(R.id.listView1);

    MyAdapter Ada = new MyAdapter(MainActivity.this,data);
    L.setAdapter(Ada);


}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

}

public class MyAdapter extends BaseAdapter {

Context context;
private ArrayList<String> data=  new ArrayList<String>();

 public MyAdapter(Context context ,ArrayList<String> data )
 {
     this.context=context;
     this.data=data;
 }


@Override
public int getCount() {
    // TODO Auto-generated method stub
    return 0;
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    return null;
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub
    ViewHolder holder; 
    convertView = null;
    if (convertView == null) {
        convertView = LayoutInflater.from(context)
          .inflate(R.layout.listlayout, parent, false);

        holder = new ViewHolder(); 

        holder.mainpic = (ImageView)convertView.findViewById(R.id.imageView1);
        holder.text= (TextView)convertView.findViewById(R.id.textView1);
        convertView.setTag(holder); 
    } 
    else
    {
        holder = (ViewHolder) convertView.getTag();

    }

    holder.text.setText(this.data.get(position));


    return convertView;
}







static class ViewHolder {            

    ImageView mainpic; 
    TextView text;
} 

}

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:paddingBottom="@dimen/activity_vertical_margin"
  android:paddingLeft="@dimen/activity_horizontal_margin"
  android:paddingRight="@dimen/activity_horizontal_margin"
  android:paddingTop="@dimen/activity_vertical_margin"
 tools:context=".MainActivity" >

<ListView
    android:id="@+id/listView1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true" >

 </ListView>

</RelativeLayout>

Answer 1

Change getCount() to this:

@Override
public int getCount() {
    return data.size();
}

Currently, you always return 0, which tells the ListView that there are no items to display.

Also, you might consider actually implementing getItem():

@Override
public Object getItem(int position) {
    return data.get(position);
}

And use that to get your items anywhere else.

Answer 2

Don't set convertView null explicitly it will come null only for first time your getView will be called, else it will result in performance issue

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

     ViewHolder holder; 

     if (convertView == null) {
       convertView = LayoutInflater.from(context)
      .inflate(R.layout.listlayout, parent, false);

       holder = new ViewHolder(); 

        holder.mainpic = (ImageView)convertView.findViewById(R.id.imageView1);
        holder.text= (TextView)convertView.findViewById(R.id.textView1);
        convertView.setTag(holder); 
     } else {
        holder = (ViewHolder) convertView.getTag();
     }

     holder.text.setText(this.data.get(position));

     return convertView;
  }

Also make these changes in your code :

@Override
public int getCount() {

    return data.size();
}

@Override
public Object getItem(int position) {

    return data.get(position);
}

@Override
public long getItemId(int position) {

    return position;
}