Gson 和方向变化的问题

Question

我正在尝试使用 Gson 保存对 POJOS 列表的序列化/反序列化。虽然通常这不是一项特殊的任务，但我遇到了一个我以前从未见过的异常​​：

01-11 14:17:22.556: E/AndroidRuntime(15941): java.lang.RuntimeException: 
Unable to start activity ComponentInfo{com.timkranen.playpalproject/com.timkranen.playpalproject.HomeActivity}: 
java.lang.RuntimeException: Unable to invoke no-args constructor for interface java.util.concurrent.locks.Lock. 
Register an InstanceCreator with Gson for this type may fix this problem.

我怀疑这与 List 项被加载到 AsyncTask 中的事实有关。有人有这个问题的经验吗？

我尝试将我在 onSaveInstanceState（用于保存）中执行的逻辑放在同步方法中，但这没有帮助。

编辑

这是我的一些代码，试图让它更清晰。我有一个名为friendsList 的列表。 List填充在这个AsyncTask中，在onCreateView()中执行

private class RetrieveFriends extends AsyncTask<Void, Integer, String> {

    @Override
    protected String doInBackground(Void... params) {
        // get friends
        if (friendProfiles == null || friendProfiles.size() == 0) {
            friendProfiles = new ArrayList<Profile>();
            if (currentProfile.getFriendUids() != null
                    && currentProfile.getFriendUids().size() > 0)
                for (String fUid : currentProfile.getFriendUids()) {
                    Profile friend = ProfileDataManager
                            .getProfileFromId(fUid);
                    friendProfiles.add(friend);
                }

            if (friendProfiles.size() == 0) {
                return "null";
            }
        }

        return "notnull";

    }

    @Override
    protected void onPostExecute(String result) {
        if (!result.equals("null")) {
            loadingFriendsBar.setVisibility(View.INVISIBLE);
            friendsList.setVisibility(View.VISIBLE);
            FriendListAdapter adapter = new FriendListAdapter(
                    containedActivity, R.layout.friendslist_row,
                    friendProfiles);
            friendsList.setAdapter(adapter);
        } else {
            loadingFriendsBar.setVisibility(View.INVISIBLE);
            friendMsg.setVisibility(View.VISIBLE);
        }
    }

}

现在在 onSaveInstanceState 中，我将 List 序列化为 JSON，如下所示：

private synchronized void saveToState(Bundle state) {
    Gson gson = new Gson();
    Type listOfProfiles = new TypeToken<List<Profile>>() {
    }.getType();
    String json = gson.toJson(friendProfiles, listOfProfiles);
    state.putString("json_friendProfiles", json);
}

该方法直接在 onSaveInstanceState() 中调用。检索是一样的：

private synchronized void retrieveFromState(String json) {
    Type listOfProfiles = new TypeToken<List<Profile>>() {
    }.getType();
    Gson gson = new Gson();
    friendProfiles = (List<Profile>) gson.fromJson(json,
            listOfProfiles);
}

奇怪的是，当导航到不同的 Fragment 时，状态会正确保存。该错误仅在我更改方向时发生。

编辑：根据要求，这里是 Profile 类

public class Profile {

private String mEmail;
private String mPassword;
private String uid;

// optional properties
private String name;
private String location;
private String about;
private ParseFile image; // not certain of data type

private List<String> friendUids;

public String getName() {
    if (name == null || name.equals("")) {
        return "Name unknown";
    }
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getLocation() {
    if (location == null || location.equals("")) {
        return "Location unknown";
    }
    return location;
}

public void setLocation(String location) {
    this.location = location;
}

public String getAbout() {
    if (about == null || about.equals("")) {
        return "About unknown";
    }
    return about;
}

public void setAbout(String about) {
    this.about = about;
}

public void setUid(String Uid) {
    this.uid = Uid;
}

public String getUid() {
    return this.uid;
}

public String getPassword() {
    return mPassword;
}

public String getEmail() {
    return mEmail;
}

public Profile(String email, String password) {
    this.mEmail = email;
    this.mPassword = password;
}

/*
 * Saves a Profile and returns the profiles UID This is ONLY APPLICABLE for
 * NEW profiles use the update method to update existing profile data
 */
public void saveToParse(SaveCallback saveCallBack) {
    if (ProfileDataManager.IsRegistered(this) != true) {
        ParseObject pObject = new ParseObject("Profiles");
        pObject.put("email", this.mEmail);
        pObject.put("password", this.mPassword);
        pObject.saveInBackground(saveCallBack);
    } else {
        saveCallBack.done(new ParseException(ErrorCodes.ALREADY_REGISTERED,
                "AlreadyRegistered"));
    }
}

public void update() {
    ParseQuery<ParseObject> query = ParseQuery.getQuery("Profiles");
    query.getInBackground(this.uid, new GetCallback<ParseObject>() {

        @Override
        public void done(ParseObject object, ParseException e) {
            if (e == null) {
                // update the object
                object.put("email", Profile.this.mEmail);
                object.put("password", Profile.this.mPassword);
                if (Profile.this.name != null) {
                    object.put("name", Profile.this.name);
                }
                if (Profile.this.location != null) {
                    object.put("location", Profile.this.location);
                }
                if (Profile.this.about != null) {
                    object.put("about", Profile.this.about);
                }
                if (Profile.this.image != null) {
                    object.put("profileImage", Profile.this.image);
                }
                if (Profile.this.friendUids != null
                        && Profile.this.friendUids.size() != 0) {
                    object.put("friends", Profile.this.friendUids);
                }

                object.saveInBackground();
            }
        }
    });
}

/*
 * Use updateWithCallBack when you want to update an object but want to show
 * the updated data immediatly using a callback, when calling this method
 * make sure that currentProfile in HomeActivity is set to the new Profile!
 */
public void updateWithCallBack(final SaveCallback callBack) {
    ParseQuery<ParseObject> query = ParseQuery.getQuery("Profiles");
    query.getInBackground(this.uid, new GetCallback<ParseObject>() {

        @Override
        public void done(ParseObject object, ParseException e) {
            if (e == null) {
                // update the object
                object.put("email", Profile.this.mEmail);
                object.put("password", Profile.this.mPassword);
                if (Profile.this.name != null) {
                    object.put("name", Profile.this.name);
                }
                if (Profile.this.location != null) {
                    object.put("location", Profile.this.location);
                }
                if (Profile.this.about != null) {
                    object.put("about", Profile.this.about);
                }
                if (Profile.this.image != null) {
                    object.put("profileImage", Profile.this.image);
                }
                if (Profile.this.friendUids != null
                        && Profile.this.friendUids.size() != 0) {
                    object.put("friends", Profile.this.friendUids);
                }
                object.saveInBackground(callBack);
            }
        }
    });
}

// retrieves the image, when done calls callback
public void retrieveProfileImage(GetDataCallback callBack) {
    this.image.getDataInBackground(callBack);
}

public ParseFile getProfileImage() {
    return this.image;
}

public void setProfileImage(ParseFile image) {
    this.image = image;
}

public void saveProfileImage(Bitmap image) {
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    image.compress(Bitmap.CompressFormat.JPEG, 50, stream);
    byte[] byteArray = stream.toByteArray();
    String imgid = this.getUid() + "_profile_image.jpeg";
    String fileNameForImage = this.getUid() + "_profile_image.jpeg";
    this.image = new ParseFile(fileNameForImage, byteArray);
}

public List<String> getFriendUids() {
    return this.friendUids;
}

public void addFriend(String uid) {
    if (this.friendUids != null) {
        friendUids.add(uid);
    } else {
        friendUids = new ArrayList<String>();
        friendUids.add(uid);
    }
}

public void setFriends(Object friends) {
    ArrayList<String> f = (ArrayList<String>) friends;
    this.friendUids = f;
}

}

Answer 1

Gson 对象

private Gson gson = new GsonBuilder().
        setExclusionStrategies(new ParseExclusion()).
        create();

排除类

private class ParseExclusion implements ExclusionStrategy {

    public boolean shouldSkipClass(Class<?> arg0) {
        return false;
    }

    public boolean shouldSkipField(FieldAttributes f) {
        return (f.getDeclaredClass() == Lock.class);
    }

}

最后：

Type type = new TypeToken<List<Profile>>() {}.getType();
List<Profile>) friendProfiles = new ArrayList<Profile>();
friendProfiles = gson.fromJson(json,type);