在另一项活动/课程中共享偏好

Question

我编写了一个类来处理共享首选项：

import android.preference.PreferenceManager;
import android.util.Log;
import android.content.Context;
import android.content.SharedPreferences;

public class PreferenceHandler {
    
     Context mContext = null;

        public PreferenceHandler (Context context) {
            mContext = context;
        }
       
        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(mContext);
         
        public void NewGamePrefs(){
             int GameTime=(Integer.parseInt(mContext.getString(R.string.gametime)));
             int Trivianten=(Integer.parseInt(mContext.getString(R.string.trivialocations)));
             SharedPreferences.Editor memory = preferences.edit();
             memory.putInt("GameTime" , GameTime);
             memory.putInt("Score", 0);
             GPSHandler MyGPS=new GPSHandler(mContext);
             memory.putString("StartLocation", MyGPS.getStartLocationID());
             memory.putString("NextLocation", MyGPS.getStartLocationID());
             memory.putString("EndLocation", MyGPS.getEndLocationID());
        commit();
            }
        
        public String getPreferenceString(String KEY){
            return preferences.getString(KEY, "nodata");
        }
        
        public int getPreferenceValue(String KEY){
            return preferences.getInt(KEY, -1);
        }

如果我从活动文件中调用此类：

PreferenceHandler GameMemory=new PreferenceHandler(this);

GameMemory.NewGamePrefs();

我遇到空指针异常，有人知道为什么以及如何解决这个问题吗？

多谢！

Answer 1

您永远不会初始化首选项。将 preferences 和构造函数更改为：

SharedPreferences preferences;

public PreferenceHandler (Context context) {
    mContext = context;
    preferences = PreferenceManager.getDefaultSharedPreferences(mContext);
}