[英]Gson type cast error
java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to anindya.fb.datamodel.Datum
I have a HashMap
: 我有一个HashMap
:
static HashMap<String, Datum> favoriteList = new HashMap<>();
and I write it to GSON in the following way: 然后通过以下方式将其写入GSON:
String json = gson.toJson(favoriteList);
mEditor.putString(PREF_FAVORITE, json);
mEditor.commit();
and get it like this: 并得到这样的:
gson = new Gson();
String json = mPref.getString(PREF_FAVORITE, "");
if (json.equals(""))
favoriteList = new HashMap<>();
else
favoriteList = gson.fromJson(json, HashMap.class);
To send back a part of this HashMap
based on a value, I am doing this: 要基于值发回此HashMap
的一部分,我正在这样做:
ArrayList<Datum> data = new ArrayList<>();
for(String key: favoriteType.keySet()) {
if(favoriteType.get(key).equals(type)) { //type is a parameter to this method
data.add(favoriteList.get(key));
}
}
return data;
However when I try to access this data, I get this error: 但是,当我尝试访问此数据时,出现此错误:
final Datum curData = data.get(position);
gives an error: 给出一个错误:
java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to anindya.fb.datamodel.Datum
I came across some posts which mention adding lines in the proguard
file. 我遇到了一些帖子,提到在proguard
文件中添加行。
-keepattributes *Annotation*
# Gson specific classes
-keep class sun.misc.Unsafe { *; }
#-keep class com.google.gson.stream.** { *; }
# Application classes that will be serialized/deserialized over Gson
-keep class com.google.gson.examples.android.model.** { *; }
but that did not fix the error. 但这并不能解决错误。 Any help would be appreciated. 任何帮助,将不胜感激。
The issue is you're storing a hashmap with type information that's getting dropped when you're reading it. 问题是您存储的哈希图的类型信息在读取时会被丢弃。
Change 更改
favoriteList = gson.fromJson(json, HashMap.class);
to 至
favoriteList = gson.fromJson(json, new TypeToken<HashMap<String, Datum>>(){}.getType);
You need to get the type of
HashMap<String, Datum>
so do this,Type type = new TypeToken<HashMap<String, Datum>>(){}.getType();
您需要获取HashMap<String, Datum>
的类型,执行此操作,Type type = new TypeToken<HashMap<String, Datum>>(){}.getType();
then 然后
favoriteList = gson.fromJson(json, type);
Try something like this... 试试这样的东西...
public Map<String, Datum> toMap(String jsonString) {
Type type = new TypeToken<Map<String, Datum>>(){}.getType();
Gson gson = new GsonBuilder().create();
Map<String, Datum> map = gson.fromJson(jsonString, type);
return map;
}
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