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POandroid: why are no elements appearing in my listview?
 

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  1. POandroid: why are no elements appearing in my listview?
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    <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>
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    1. COYou call `super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);` twice, take that out -it's redundant. Just a code tip.
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    2. COoops, thanks for pointing out the silly mistake!
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      1. USdrewmoore
 

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