1

我将 sharedPreferences 中的值保存在一个类中，并尝试从另一个类访问它但得到空指针异常。我输入的值是 Web 服务的 url。请帮我。

网址设置.java

public class UrlSetting extends Activity {
EditText editUrl;
TextView Savedurl;
Button bSaveUrl, bback;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.urlsetting);

    Savedurl = (TextView)findViewById(R.id.savedurl);
    editUrl = (EditText)findViewById(R.id.editurl);
    bback = (Button)findViewById(R.id.back);
    bSaveUrl = (Button)findViewById(R.id.saveurl);
    bSaveUrl.setOnClickListener(buttonSaveUrlOnClickListener);
    bback.setOnClickListener(new Button.OnClickListener(){

        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            Intent intent = new Intent(UrlSetting.this, Login.class);
            /*intent.setClass(UrlSetting.this, Login.class);*/
            startActivity(intent);
        }});

    LoadPreferences();
}
Button.OnClickListener buttonSaveUrlOnClickListener
= new Button.OnClickListener(){

    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        SavePreferences("URL", editUrl.getText().toString());
        LoadPreferences();
    }

private void SavePreferences(String key, String value){
    SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPreferences.edit();
    editor.putString(key, value);
    editor.commit();
}

private void LoadPreferences(){
    SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
    String strSavedurl = sharedPreferences.getString("URL", "");
    Savedurl.setText(strSavedurl);
}

这是我的 Koneksi.java

public class Koneksi{

SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
String url = sharedPreferences.getString("URL", "");
public Koneksi(String urlml){

    url= url + urlml;
}

public String getUrl(){

    return url;
}

这是 LogCat

> 05-21 11:39:44.542: W/KeyCharacterMap(339): No keyboard for id 0
05-21 11:39:44.542: W/KeyCharacterMap(339): Using default keymap: /system/usr/keychars/qwerty.kcm.bin
05-21 11:39:51.826: D/TryLoginCheck(339): Here
05-21 11:39:51.826: I/System.out(339): UserNametes
05-21 11:39:51.831: I/System.out(339): passwordTes12345*
05-21 11:39:51.831: D/Parameters(339): username=tes&password=Tes12345*
05-21 11:39:51.831: D/AndroidRuntime(339): Shutting down VM
05-21 11:39:51.831: W/dalvikvm(339): threadid=1: thread exiting with uncaught exception (group=0x40015560)
05-21 11:39:51.851: E/AndroidRuntime(339): FATAL EXCEPTION: main
05-21 11:39:51.851: E/AndroidRuntime(339): java.lang.NullPointerException
05-21 11:39:51.851: E/AndroidRuntime(339):  at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:146)
05-21 11:39:51.851: E/AndroidRuntime(339):  at mobile.config.Koneksi.<init>(Koneksi.java:13)
05-21 11:39:51.851: E/AndroidRuntime(339):  at com.karismaelearning.Login.tryLogin(Login.java:131)
05-21 11:39:51.851: E/AndroidRuntime(339):  at com.karismaelearning.Login$3.onClick(Login.java:80)
05-21 11:39:51.851: E/AndroidRuntime(339):  at android.view.View.performClick(View.java:2485)
05-21 11:39:51.851: E/AndroidRuntime(339):  at android.view.View$PerformClick.run(View.java:9080)
05-21 11:39:51.851: E/AndroidRuntime(339):  at android.os.Handler.handleCallback(Handler.java:587)
05-21 11:39:51.851: E/AndroidRuntime(339):  at android.os.Handler.dispatchMessage(Handler.java:92)
05-21 11:39:51.851: E/AndroidRuntime(339):  at android.os.Looper.loop(Looper.java:123)
05-21 11:39:51.851: E/AndroidRuntime(339):  at android.app.ActivityThread.main(ActivityThread.java:3683)
05-21 11:39:51.851: E/AndroidRuntime(339):  at java.lang.reflect.Method.invokeNative(Native Method)
05-21 11:39:51.851: E/AndroidRuntime(339):  at java.lang.reflect.Method.invoke(Method.java:507)
05-21 11:39:51.851: E/AndroidRuntime(339):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-21 11:39:51.851: E/AndroidRuntime(339):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-21 11:39:51.851: E/AndroidRuntime(339):  at dalvik.system.NativeStart.main(Native Method)
05-21 11:39:54.301: I/Process(339): Sending signal. PID: 339 SIG: 9

请帮助我知道错误是什么。我不明白出了什么问题。非常感谢您

4

6 回答 6

0

SharedPreference 在您的应用程序中很常见，您可以在应用程序的任何位置使用，

http://developer.android.com/reference/android/content/SharedPreferences.html

于 2013-05-21T04:58:47.220 回答
0

我不知道你的代码有什么问题，我有同样的工作实现..

    public class GreetingCardData {
    public static final String SHARED_PREF_FILE     =   "greetingCardData";
    public static final String KEY_DO_NOT_SHOW      =   "doNotShow";
    public static final String KEY_CATEGORIES_JSON  =   "categoriesJson";   
    private SharedPreferences sharedPrefs;
    private Editor prefsEditor;

    public GreetingCardData(Context context) {
        this.sharedPrefs = context.getSharedPreferences(SHARED_PREF_FILE, 0);
        this.prefsEditor = sharedPrefs.edit();
    }   

    public void setDoNotShowFlag ( boolean flag ){
        prefsEditor.putBoolean( KEY_DO_NOT_SHOW, flag );
        prefsEditor.commit();
    }

    public boolean getDoNotShowFlag(){
        return sharedPrefs.getBoolean( KEY_DO_NOT_SHOW, false );
    }

    public void setGreetingcardJson( String jsonString ){
        prefsEditor.putString( KEY_CATEGORIES_JSON, jsonString );
        prefsEditor.commit();
    }

    public String getGreetingcardJsonString(){
        return sharedPrefs.getString(KEY_CATEGORIES_JSON, "");
    }    
}

你可以访问你的偏好。任何地方只要调用它就像..

if( !new GreetingCardData(ActivityMain.this).getDoNotShowFlag())
     startHomeActivity();   


new GreetingCardData(context).setGreetingcardJson(resBuffer.toString());
于 2013-05-21T10:47:38.100 回答
0

试试这两种方法：p 效果很好

public static void SavePreferences(String key, String name, String value,Context c) {
    SharedPreferences sf = c.getSharedPreferences(key, 0);
    SharedPreferences.Editor editor = sf.edit();
    editor.putString(name, value);
    editor.commit();
    Log.w("Preference saved  .", value);

}

public static String LoadPreferences(String key, String name, Context c) {
    SharedPreferences sf = c.getSharedPreferences(key, 0);
    String val = null;
    val = sf.getString(name, "");
    return val;

}
于 2013-05-21T04:39:41.100 回答
0

这些会给你NPE

SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);                                                          
String url = sharedPreferences.getString("URL", "");

移动onCreate()我看不到的初始化，但假设你有，因为你正在扩展Activity

public class Koneksi extends Activity {

    SharedPreferences sharedPreferences; //declare them here
    String url;

    public void onCreate(Bundle bundle)
   {
        super.onCreate(bundle);
        setContentView(R.layout.your_layout);

       sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);  // initialize them here
       url = sharedPreferences.getString("URL", "");  // intialize here

    public Koneksi(String urlml){   
        url= url + urlml;
    }

SharedPreferences需要 a在调用Contextafter 之前不可用。onCreate()您可以按原样在此之前声明它们，但您需要在其中初始化它们onCreate()或调用其他Activity方法onCreate()

于 2013-05-21T04:41:26.577 回答
0 
   - you should be pass the context 



   mContext.getSharedPreferences(PREF_NAME, MODE_PRIVATE);




  other wise use following code :-
  import android.preference.PreferenceManager;
  SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
  // then you use
  prefs.getBoolean("keystring", true);
于 2013-05-21T04:47:28.380 回答
0

试试这种方式：

SharedPreferences sharedPreferences;

onCreate(Bundle savedInstanceState){
  sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
  // your code..
}

private void SavePreferences(String key, String value){

    SharedPreferences.Editor editor = sharedPreferences.edit();
    editor.putString(key, value);
    editor.commit();
}

private void LoadPreferences(){

    String strSavedurl = sharedPreferences.getString("URL", "");
    Savedurl.setText(strSavedurl);
}

编辑：

    public class Koneksi{

    SharedPreferences sharedPreferences;
    Context myC;
    String url = "";

    public Koneksi(Context con){
       myC = con;
       sharedPreferences = PreferenceManager.getDefaultSharedPreferences(con);
    }


    public Koneksi(String urlml){

        url= url + urlml;
    }


    public String getUrl(){
        String url = sharedPreferences.getString("URL", "");
        return url;
    }
}

从活动中调用上述类：

Koneksi ob = new Koneksi(this);
String URL = ob.getUrl();
于 2013-05-21T04:54:46.863 回答