空指针异常，而从共享首选项获取值

在我的主要活动，我想获取存储在共享首选项中的值，值存储在其中一个分区，但是当我运行该应用程序时，它给了我NPE，代码在这里我想获得的值是：空指针异常，而从共享首选项获取值

spref=new SharedPref(getApplicationContext()); 
     // get user data from session 
      HashMap<String, Integer> selection = spref.GetPeerSelection(); 

      // name 
    int selec = selection.get(SharedPref.KEY_SelectionId); 
      // Save the Data in Database 
      if(selec==1) 
      // Toast.makeText(getApplicationContext(),"1", Toast.LENGTH_LONG).show(); 

       if(selec==0) 
       // Toast.makeText(getApplicationContext(),"0", Toast.LENGTH_LONG).show();

我的共享偏好类是：

public class SharedPref { 
    // Shared Preferences 
    SharedPreferences pref; 
    Context _context; 
    int PRIVATE_MODE = 0; 
    // Editor for Shared preferences 
    Editor editor; 
    private static final String PREF_NAME = "Settings"; 

    // All Shared Preferences Keys 


    // User name (make variable public to access from outside) 
    public static final String KEY_NAME = "name"; 
    public static final String KEY_MessageId = "msgid"; 
    public static final String KEY_SelectionId = "selectionid"; 
    // Email address (make variable public to access from outside) 
// public static final String KEY_HOPCOUNT = "hopcount"; 
    // public static final String KEY_RANK = "rank"; 



    public SharedPref(Context context){ 
     this._context = context; 
     pref = _context.getSharedPreferences(PREF_NAME, PRIVATE_MODE); 

     editor = pref.edit(); 
    } 


    /* public void SaveRank(int rank) 

    { 
     editor.putInt(KEY_RANK, rank); 

    } 

    */ 
    public void SaveSettings(String name){ 

     // Storing name in pref 
     editor.putString(KEY_NAME, name); 

     // editor.putInt(KEY_HOPCOUNT, HopCount); 
     // commit changes 
     editor.commit(); 
    } 
    public void messageno(float msgno) 

    { 
     editor.putFloat(KEY_MessageId, msgno); 

     editor.commit(); 
    } 
    public void PeerSelection(int selection) 

    { 
    editor.putInt(KEY_SelectionId, selection); 

    editor.commit(); 
    } 

    public HashMap<String, String> getUserName(){ 
     HashMap<String, String> user = new HashMap<String, String>(); 
     // user name 
     user.put(KEY_NAME, pref.getString(KEY_NAME, null)); 



     // return user 
     return user; 
    } 

    public HashMap<String, Float> getMessageId(){ 
     HashMap<String, Float> id = new HashMap<String, Float>(); 
     // Message No 
     id.put(KEY_MessageId, pref.getFloat(KEY_MessageId,0.0f)); 



     // return user 
     return id; 
    } 
    public HashMap<String, Integer> GetPeerSelection(){ 
     HashMap<String, Integer> selection = new HashMap<String, Integer>(); 
     // Message No 
     selection.put(KEY_SelectionId, pref.getInt(KEY_SelectionId,(Integer) null)); 

     // return user 
     return selection; 
    } 

}

我的日志猫是：

12-10 11:47:16.624: E/AndroidRuntime(6029): FATAL EXCEPTION: main 
12-10 11:47:16.624: E/AndroidRuntime(6029): java.lang.RuntimeException: Unable to start activity ComponentInfo{soft.b.peopleassist/soft.b.peopleassist.MainActivity}: java.lang.NullPointerException 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2084) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2111) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.app.ActivityThread.access$600(ActivityThread.java:134) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1251) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.os.Handler.dispatchMessage(Handler.java:99) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.os.Looper.loop(Looper.java:137) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.app.ActivityThread.main(ActivityThread.java:4666) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at java.lang.reflect.Method.invokeNative(Native Method) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at java.lang.reflect.Method.invoke(Method.java:511) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at dalvik.system.NativeStart.main(Native Method) 
12-10 11:47:16.624: E/AndroidRuntime(6029): Caused by: java.lang.NullPointerException 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at soft.b.peopleassist.SharedPref.GetPeerSelection(SharedPref.java:98) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at soft.b.peopleassist.MainActivity.onCreate(MainActivity.java:140) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.app.Activity.performCreate(Activity.java:4510) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1050) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2048) 
12-10 11:47:16.624: E/AndroidRuntime(6029):  ... 11 more

来源

2013-12-10 Talib

SharedPreference#getInt(String, int)需要原型int作为参数。当通过null作为Integer这是自动拆箱，但null是不是一个有效的值为int，所以它会抛出一个NullPointerException。

来源

2013-12-10 07:14:46

selection.put(KEY_SelectionId, pref.getInt(KEY_SelectionId,(Integer) null));

你把null作为默认值..

来源

2013-12-10 07:09:54

 
selection.put(KEY_SelectionId, pref.getInt(KEY_SelectionId,(Integer) null));

而不是返回空整型，返回0或-1或任何其它号码。

错误是由于上面的代码。

来源

2013-12-10 07:13:04

您正在试图通过NULL到getInt方法

SharedPreferences.getInt的语法

公共抽象INT getInt（String键，诠释利用DefValue）

指望它INT（原始数据类型）值，但是您传递的是NULL对象，不支持

为了说明非常简单的行为，下面的代码将给你NPE

public static void main(String[] args) { 
     print((Integer)null); 
    } 
    public static void print(int i){ 
     System.out.println(i); 
    }

来源

2013-12-10 07:15:44

空指针异常，而从共享首选项获取值

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