Convert JsonString to a custom java ArrayList

问题

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

回答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.

来源：https://stackoverflow.com/questions/20847997/convert-jsonstring-to-a-custom-java-arraylist

标签

java

android

json

arraylist