android: why are no elements appearing in my listview?
<p>I'm trying to use a ListView as the main navigation feature in a magazine-reader app. I want each View in the list to display the headline of a story below an image associated with it. I have created an XML layout with a vertically-oriented LinearLayout with an ImageView on top and TextView on the bottom, and am trying to create a custom adapter that inflates this layout in the getView method and puts the image/text resources into it. Here is my code: </p>

<pre><code>package com.example.caliber;
import java.util.List;
import com.example.caliber.R;

public class MainActivity extends Activity {
Spinner issues, sections;
Button blog;
ListView mainGal;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    String[] issueList = {"issues", "fall '12", "spring '12", "fall '11", "spring '12", 
                            "fall '10", "spring '10"};
    String[] sectionList = {"sections", "campus", "entertainment", "lifestyle", "love&amp;sex", "tech&amp;web", "Current" };

    ArrayAdapter&lt;String&gt; aaIssues = new ArrayAdapter&lt;String&gt;(this, R.layout.spin_item, issueList);
    ArrayAdapter&lt;String&gt; aaSections = new ArrayAdapter&lt;String&gt;(this,   
R.layout.spin_item, sectionList);

    blog = (Button)findViewById(R.id.blogBtn);

    issues = (Spinner)findViewById(R.id.issueSpin);
    sections = (Spinner)findViewById(R.id.sectionSpin);             
    issues.setAdapter(aaIssues);
    sections.setAdapter(aaSections);


    OnClickListener mbListener = new OnClickListener() {
        @Override
            public void onClick(View v){
        issues.setAlpha((float) 0.5);
        sections.setAlpha((float) 0.5);
        blog.setAlpha((float) 0.5);
        }
     };


    ImageButton mainbtn = (ImageButton)findViewById(R.id.cbutton);      
    mainbtn.setOnClickListener(mbListener);

    mainGal = (ListView)findViewById(R.id.mainGal);
    GalAdapter ga = new GalAdapter();
    mainGal.setAdapter(ga);

}

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

class GalAdapter extends ArrayAdapter&lt;String&gt; {
    Activity context;
    String[] headlines = {"Alpha bravo charlie delta", "Echo foxtrot golf 
hotel", "indigo juliette kilo lima"};
    int[] images = {R.drawable.img1, R.drawable.img2, R.drawable.img3};

    public GalAdapter() {
        super (MainActivity.this, R.layout.galleryview);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent){
        LayoutInflater li = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);         
        View story = li.inflate(R.layout.galleryview, parent);
        ImageView image = (ImageView)story.findViewById(R.id.image);
        TextView headline = (TextView)story.findViewById(R.id.headline);

        image.setImageResource(images[position]);
        headline.setText(headlines[position]);
        return story;       
}   
</code></pre>

<p>The app launches fine and I can see the listview's background, but there are no items on the list. Why is this? As is probably clear, I'm very new to android development, but have a good understanding of the fundamentals of Java. I'm aware this is due to a fundamental misunderstanding I have here, perhaps an error in one of the constructors (I'm still a little fuzzy on what some of the parameters are). Anyway, I'll be very appreciative if anyone can help me understand these issues more deeply. </p>

<p>Thanks in advance</p>

<p>p.s. is it poor form to categorize this under both android and java? should I just use android in the future?</p>

<p>---EDIT:</p>

<pre><code>    class GalAdapter extends ArrayAdapter&lt;String&gt; {
    Activity context;
    String[] hlines;
    int[] imgs;

    public GalAdapter(String[] hlines, int[] imgs) {
        super (MainActivity.this, R.layout.galleryview , hlines);
        this.hlines = hlines;
        this.imgs = imgs;
    }       
    @Override
    public View getView(int position, View convertView, ViewGroup parent){
        if (convertView == null){
        LayoutInflater li = (LayoutInflater)context. getSystemService (Context.LAYOUT_INFLATER_SERVICE);
        convertView = li.inflate(R.layout.galleryview, parent);
        ImageView image = (ImageView)convertView.findViewById(R.id.image);
        TextView headline = (TextView)convertView.findViewById(R.id.headline);

        image.setImageResource(imgs[position]);
        headline.setText(hlines[position]);}
        return convertView;                                 
    }
    }
</code></pre>

<p>Now I'm getting a null pointer exception on the line where I call the LayoutInflator. What pointer is it referring to? I'm assuming I'm not passing the arrays (String[] hlines + int[] imgs) into it properly... Here is where I make the call: </p>

<pre><code>    String[] headlines ={ "Echo foxtrot golf hotel", "Echo foxtrot golf hotel", "indigo   
juliette kilo lima"};
    int[] images = {R.drawable.img1, R.drawable.img2, R.drawable.img3};
            ....
    mainGal = (ListView)findViewById(R.id.mainGal);
    GalAdapter ga = new GalAdapter(headlines, images);
    mainGal.setAdapter(ga);
</code></pre>
