ArrayList的迭代器错误：无法将java.util.LinkedHashMap强制转换为MyObject

Question

I have the following problem in Android: I store some data as an ArrayList in a Couchbase lite document:

ArrayList<FluxDocReg> list_flux = (ArrayList<FluxDocReg>)doc.getProperty("flux");
if (list_flux == null)
    list_flux = new ArrayList<FluxDocReg>();

FluxDocReg flux = new FluxDocReg();
//.....
list_flux.add(flux);
//save 'list_flux' in document
...

so until I have an ArrayList of LinkedHashedMap objects instead of FluxDocReg.

Next, I read the property:

if (documentBD != null && documentBD.getProperty("flux") != null)
{
    ArrayList<FluxDocReg> list_flux = ArrayList<FluxDocReg>)documentBD.getProperty("flux");
    ///*****there are some objects in ArrayList, each of type LinkedHashedMap instead of FluxDocReg 
for (int i = 0; i < list_flux.size(); i++)
    {
        ****ERROR****     FluxDocReg flux = (FluxDocReg)list_flux.get(i);
    }
}

I get an error when it tries to cast "FluxDocReg flux = (FluxDocReg)list_flux.get(i)"

I know that there are some objects in ArrayList, each of type LinkedHashedMap instead of FluxDocReg...

What did I do wrong and how can I fix it?

Thanks, Catalin

Answer 1

Apparently there is something called "Java Type Erasure" for generics (lists of generics), so I had to come with a workaround. Something like this, involving reflection and conversion to-and-from JSON:

List<FluxDocRegInfo> list_flux = null;

if (obj != null) {

    //USING REFLECTION FOR AVOIDING TYPE ERASURE
    Type listType = new TypeToken<ArrayList<FluxDocRegInfo>>() {}.getType();
    list_flux = new Gson().fromJson(obj.toString(), listType);
}
else //flux is null
{
    list_flux = new ArrayList<FluxDocRegInfo>();
}
///add something to the list
list_flux.add(flux);

JsonElement element = new Gson().toJsonTree(list_flux, new com.google.common.reflect.TypeToken<List<FluxDocRegInfo>>() {}.getType());
JsonArray jsonArray = element.getAsJsonArray()