我将一个类中的sharedPreferences中的值保存并尝试从另一个类中访问它 class但得到空指针异常。我输入的值是网络服务的网址。请帮帮我。
UrlSetting.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
答案 0 :(得分：0)
尝试以下两种方法：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;
}
答案 1 :(得分：0)
这些将为您提供NPE
SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
String url = sharedPreferences.getString("URL", "");
将初始化移至onCreate()我看不到，但假设您已经扩展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Context，直到调用onCreate()后才能使用onCreate()。您可以在此之前声明它们，但是在调用Activity后需要在onCreate()或其他{{1}}方法中初始化它们
答案 2 :(得分：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);
答案 3 :(得分：0)
尝试这种方式：
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;
}
}
来自活动的上述课程：
Koneksi ob = new Koneksi(this);
String URL = ob.getUrl();
答案 4 :(得分：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
答案 5 :(得分：0)
我不知道您的代码有什么问题，我的工作实现相同..
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, "");
}
}
您可以访问您的首选项。任何地方只需称它为......
if( !new GreetingCardData(ActivityMain.this).getDoNotShowFlag())
startHomeActivity();
new GreetingCardData(context).setGreetingcardJson(resBuffer.toString());