putExtra treeMap returns HashMap cannot be cast to TreeMap android

Question

I need your help, I cannot understand what's happening?

I'm trying to send a TreeMap between 2 activities, the code is something like this:

class One extends Activity{
 public void send(){
   Intent intent = new Intent(One.this, Two.class);
   TreeMap<String, String> map = new TreeMap<String, String>();
   map.put("1","something");
   intent.putExtra("map", map);
   startActivity(intent);
   finish();
 }
}

class Two extends Activity{
  public void get(){
  (TreeMap<String, String>) getIntent().getExtras().get("map");//Here is the problem
  }
}

This returns to me HashMap cannot be cast to TreeMap. What

For the gory details of what is happening, see my answer here: http://stackoverflow.com/questions/12300886/linkedlist-put-into-intent-extra-gets-recast-to-arraylist-when-retrieving-in-nex/12305459#12305459 — David Wasser, Dec 19 '12 at 20:25

score 3 · Accepted Answer · answered Dec 19 '12 at 20:30

As alternative to @Jave's suggestions, if you really need the data structure to be a TreeMap, just use the appropriate constructor that takes another map as data source. So on the receiving end (Two) do something like:

public class Two extends Activity {
    @Override public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TreeMap<String, String> map = new TreeMap<String, String>((Map<String, String>) getIntent().getExtras().get("map"));
    }
}

However, depending on your project, you probably don't have to worry about the exact Map implementation. So in stead, you could just cast to the Map interface:

public class Two extends Activity {
    @Override public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Map<String, String> map = (Map<String, String>) getIntent().getExtras().get("map");
    }
}

score 1 · Answer 2 · answered Dec 19 '12 at 20:05

1

Sounds like it serializes to a HashMap and that's what you're getting. Guess you're gonna have to settle for a HashMap. Alternatively you can create your own helper class and implement Parcelable, then serialize the key/strings in order.

answered Dec 19 '12 at 20:05

dmon

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When you put anything that implements the `Map` interface into a `Bundle`, it comes out as a HashMap. Same with `List` - you always get an `ArrayList` out of it. See http://stackoverflow.com/questions/12300886/linkedlist-put-into-intent-extra-gets-recast-to-arraylist-when-retrieving-in-nex/12305459#12305459 – David Wasser Dec 19 '12 at 20:32
Cool, thanks for the explanation, I suspected something along this lines. It's good to know that a plain HashMap is supported, though. – dmon Dec 19 '12 at 21:46

score 0 · Answer 3 · answered Dec 19 '12 at 20:13

Instead of casting the result directly to a TreeMap, you can create a new TreeMap<String, String> and use the putAll()-method:

TreeMap<String, String> myMap = new TreeMap<String, String>;
HashMap<String, String> receivedMap = getIntent().getExtras().get("map");
myMap.putAll(receivedMap);

putExtra treeMap returns HashMap cannot be cast to TreeMap android

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