I am getting
java.lang.ClassCastException: java.util.HashMap cannot be cast to java.util.LinkedHashMap
at LinkedHashMap<String, String> dataHashMap = (LinkedHashMap<String, String>) intent.getSerializableExtra("tests.test.MyApp.A.EXTRA_KEY");
in the given (relevant parts of) code of Activity B.
In Fragment A, I have the following check:
Log.i(TAG, "THE TYPE OF THE MAP RETURNED FROM populateSelectedEntryList(selectedResultEntry) IS " + populateSelectedEntryList(selectedResultEntry).getClass().getSimpleName() + ".");//******PRINTS LinkedHashMap**********************
which prints LinkedHashMap
.
In Activity B, I have the following check:
LinkedHashMap<String, String> dataHashMap = (LinkedHashMap<String, String>)intent.getSerializableExtra("tests.test.MyApp.A.EXTRA_KEY");//**********ClassCastException*****************
which prints HashMap
.
The question is why? Why is the system converting my LinkedHashMap to HashMap. How do i force the LinkedHashMap to continue to be a LinkedHashMap when it is passed in an intent as a Serializable?
RELEVANT PARTS OF CODE:
In Fragment A,
public class A extends Fragment {
...
public void onListItemClick(...) {
Intent intent = new Intent(getActivity(), B.class);
...
intent.putExtra("tests.test.MyApp.A.EXTRA_KEY", populateSelectedEntryList(selectedResultEntry));
Log.i(TAG, "THE TYPE OF THE MAP RETURNED FROM populateSelectedEntryList(selectedResultEntry) IS "
+ populateSelectedEntryList(selectedResultEntry).getClass().getSimpleName() + ".");//******PRINTS LinkedHashMap**********************
startActivity(intent);
};
...
private LinkedHashMap<String, String> populateSelectedEntryList(MyParser.Entry selectedResultEntry) {
LinkedHashMap<String, String> selectedEntryMap = new LinkedHashMap<>();
...
return selectedEntryMap;
}
}
And inside Activity B,
public class B extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
...
Intent intent = getIntent();
LinkedHashMap<String, String> dataHashMap = (LinkedHashMap<String, String>) intent.getSerializableExtra("tests.test.MyApp.A.EXTRA_KEY");
} //**********ClassCastException*****************
...
}
The explanation for this is given here: LinkedList put into Intent extra gets recast to ArrayList when retrieving in next activity
If you want to recover a LinkedList
, or a Map
where the order of the keys is not important, you can use the solution of @schtever. If you want to recover a LinkedHashMap
or a TreeMap
and the order of the keys is important, it is a bit more tricky.
One possible solution is to convert the Map
into a pair of List
s, as demonstrated below:
Activity1:
public class Activity1 extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Map<Integer, String> map = new LinkedHashMap<Integer, String>();
map.put(1, "ONE");
map.put(2, "TWO");
map.put(3, "THREE");
ArrayList<Integer> keys = new ArrayList<Integer>();
ArrayList<String> values = new ArrayList<String>();
for (Map.Entry<Integer, String> entry : map.entrySet()) {
keys.add(entry.getKey());
values.add(entry.getValue());
}
Intent intent = new Intent(this, Activity2.class);
intent.putExtra("KEYS", keys);
intent.putExtra("VALUES", values);
startActivity(intent);
}
}
Activity2:
public class Activity2 extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent intent = getIntent();
List<Integer> keys = (List<Integer>) intent.getSerializableExtra("KEYS");
List<String> values = (List<String>) intent.getSerializableExtra("VALUES");
Map<Integer, String> map = new LinkedHashMap<Integer, String>();
for (int i = 0, n = keys.size(); i < n; i++)
map.put(keys.get(i), values.get(i));
Log.i("Activity2", "" + map);
}
}
This is a bit of a hack, and it's extremely verbose, but it works. I would be interested to know if there is a better solution to this.
如果排序不重要,请使用返回的 HashMap 重新创建 LinkedHashMap:
LinkedHashMap<String, String> dataHashMap = new LinkedHashMap(intent.getSerializableExtra("tests.test.MyApp.A.EXTRA_KEY"));
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