android XML parse into Hash map not working

Question

I am getting the most bizzarre behavior with trying to parse an XML, I run through it step by step and all values are assigned and retrieved in order and then the object I create is added to a HashMap for easy look up, the problem is when I am done retrieving it all the HashMap has null values and the ones that aren't null are the value of the very last node that was read, I have walked through it over and over and it all seems correct, but when it's done loading the values in the HasMap look like:

[0] null
[1] NarrationItem@44e9d170
[2] null
[3] null
[4] NarrationItem@44e9d170

etc, etc.

The format of my XML files is:

<narrations>
    <narration id="0" name="A" alias="a" >
        <line text="This is a test."></line>
    </narration>
    <narration id="1" name="B" alias="b" >
        <line text="This another a test."></line>
    </narration>
    <narration id="2" name="C" alias="c" >
        <line text="This is STILL a test."></line>
    </narration>
</narrations>

And my XML parsing method is follows:

 public HashMap<String, NarrationItem> NarrationMap = new HashMap<String, NarrationItem>();

 private void LoadNarrationsXML() {
     NarrationItem i = new NarrationItem();
     String line;
     String s;

     try {
         // Get the Android-specific compiled XML parser.
         XmlResourceParser xmlParser = this.getResources().getXml(R.xml.narrations);
         while (xmlParser.getEventType() != XmlResourceParser.END_DOCUMENT) {
             if (xmlParser.getEventType() == XmlResourceParser.START_TAG) {
                  s = xmlParser.getName();
                  if (s.equals("narration")) {
                      i.Clear();
                      i.ID  = xmlParser.getAttributeIntValue(null, "id", 0);
                      i.Name = xmlParser.getAttributeValue(null, "name");
                      i.Alias = xmlParser.getAttributeValue(null, "alias");
                  } else if (s.equals("line")) { 
                      line = xmlParser.getAttributeValue(null, "text");
                      i.Narration.add(line);
                  }
            } else if (xmlParser.getEventType() == XmlResourceParser.END_TAG) {
                  s = xmlParser.getName();
                  if (s.equals("narration")) {
                       NarrationMap.put(i.Alias, i);
                  }

             } 
             xmlParser.next();
         }
         xmlParser.close();
     } catch (XmlPullParserException xppe) {
          Log.e(TAG, "Failure of .getEventType or .next, probably bad file format");
          xppe.toString();
     } catch (IOException ioe) {
          Log.e(TAG, "Unable to read resource file");
          ioe.printStackTrace();
     }
 }

The NarrationItem object is a custom object defined as:

public class NarrationItem {

int ID;
String Name;
String Alias;
ArrayList<String> Narration = new ArrayList<String>(); 


public NarrationItem() { }

public void LoadNarration(int id, String name, String alias, ArrayList<String> narration) {

    ID = id;
    Name = name;
    Alias = alias;
    Narration.addAll(narration);// = narration;
}


public void Clear() {
    ID = 0;
    Name = "";
    Alias = "";
    Narration.clear();
}

  }//End Narration

If someone could point out the problem I'd be very thankful I have sat here staring at this issue for hours.

Jon Skeet · Accepted Answer · 2011-09-30 16:03:15Z

3

You're only ever creating one NarrationItem object - you're then using a reference to that object as the value for multiple entries in the map. Don't do that. You need to understand that the map doesn't contain an object as the value - it contains a reference to an object.

You can probably fix this just by creating a new NarrationItem each time instead of calling Clear.

It's not clear how you're looking at the map to see those null values, but if you're using the debugger and looking at the internal data structure, you probably shouldn't really be doing that either - instead, step through the keys, values or entries, i.e. stick within the abstraction that HashMap is meant to support.

answered Sep 30, 2011 at 16:03

Jon Skeet

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6 Comments

GideonKain Over a year ago

I didn't realize it was referencing the object, I made it call New NarrationItem each time and the "not null" items are now correct, Yes I was looking at the debugger to see the values in the Hashmap table It's still not quite working right, but it's atleast populating the hasmap with correct key/value pairs - thanks!

GideonKain Over a year ago

Everything appears to be working, their is no explanation for the null values in the Hashmap, but since a hashmap looks up values by key and not an index it doesn't matter - I suspect that what I am seeing isn't the true structure of the Hashmap just a way Eclipse can visualize it

Jon Skeet Over a year ago

@GideonKain: The null values in the hash map are just bits which haven't been populated - it's entirely expected that the underlying array will be relatively sparsely populated. The hash lookup uses the hash code of the key to work out which bucket to look in.

Pekka Over a year ago

@Jon completely unrelated (adding this here just because this happens to be your latest activity right now), I thought you might be intersted in contributing to this question, as there doesn't seem to be an obvious good answer. If not, just ignore me.

Jon Skeet Over a year ago

@Pekka: Interesting question - wish I knew of a standards-based answer!

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