Convert JsonString to a custom java ArrayList

Question

My qestion is, how I can convert an saved Json Sting back to an custom ArrayList.

This is how I save my ArrayList:

public void saveLocList(ArrayList<LocItem> locList) {
    SharedPreferences.Editor e = returnPref.edit();
    Gson gson = new Gson();
    String json = gson.toJson(locList);
    e.putString(LOCLIST, json);
    e.commit();
}

And now, when I restore the ArrayList (Json String) it doesn't work with this code:

public ArrayList<LocItem> getLocList() {
    String json = returnPref.getString(LOCLIST, "");
    Type type = (Type) new TypeToken<ArrayList<LocItem>>() {
    }.getType();
    ArrayList<LocItem> inpList = new Gson().fromJson(json, (java.lang.reflect.Type) type);
    return inpList;
}

This is my log:

12-30 22:19:19.395: E/AndroidRuntime(2254): FATAL EXCEPTION: main
12-30 22:19:19.395: E/AndroidRuntime(2254): java.lang.RuntimeException: Unable to start activity ComponentInfo{mypackagename.MainActivity}: java.lang.ClassCastException: com.google.gson.internal.$Gson$Types$ParameterizedTypeImpl cannot be cast to android.renderscript.Type
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2389)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.app.ActivityThread.access$600(ActivityThread.java:153)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1269)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.os.Looper.loop(Looper.java:137)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.app.ActivityThread.main(ActivityThread.java:5289)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at java.lang.reflect.Method.invokeNative(Native Method)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at java.lang.reflect.Method.invoke(Method.java:525)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at dalvik.system.NativeStart.main(Native Method)
12-30 22:19:19.395: E/AndroidRuntime(2254): Caused by: java.lang.ClassCastException: com.google.gson.internal.$Gson$Types$ParameterizedTypeImpl cannot be cast to android.renderscript.Type
12-30 22:19:19.395: E/AndroidRuntime(2254):     at mypackagename.helper.Preferences.getLocList(Preferences.java:152)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at mypackagename.MainActivity.onCreate(MainActivity.java:137)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.app.Activity.performCreate(Activity.java:5133)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-30 22:19:19.395: E/AndroidRuntime(2254):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2293)
12-30 22:19:19.395: E/AndroidRuntime(2254):     ... 11 more

I don't know what to change, maybe there is a problem with the savingformat (but it works);

Thanks

Answer 1

The error message is telling you it's a problem with casting.

TypeToken.getType() returns an object of class ParameterizedTypeImpl , which implements java.lang.reflect.Type .

However, because of an import statement that I'm assuming you have for android.renderscript.Type , Java is trying to cast the ParameterizedTypeImpl to an android.renderscript.Type .

Simply fix the import statement or use the fully qualified name ( java.lang.reflect.Type ) as you do later in the code.