Android 活动关闭时共享首选项空指针异常
我有以下代码:Android 活动关闭时共享首选项空指针异常,android,android-fragments,android-activity,nullpointerexception,android-sharedpreferences,Android,Android Fragments,Android Activity,Nullpointerexception,Android Sharedpreferences,我有以下代码: public void refresh(){ View rootView=getView(); final SharedPreferences pref = this.getContext().getSharedPreferences("MyFav", 0); final SharedPreferences.Editor editor = pref.edit(); Map<String,?> entri
public void refresh(){
View rootView=getView();
final SharedPreferences pref = this.getContext().getSharedPreferences("MyFav", 0);
final SharedPreferences.Editor editor = pref.edit();
Map<String,?> entries = pref.getAll();
final Set<String> keys = entries.keySet();}
活动中的共享首选项可能已更改。我只想在活动结束时更新首选项列表 我在按下“活动”的“后退”按钮时出现以下错误:
11-27 10:06:24.126 31645-31645/com.app.congress.congressapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.app.congress.congressapp, PID: 31645
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference
at com.app.congress.congressapp.FavLegislator.refresh(FavLegislator.java:85)
at com.app.congress.congressapp.legislator_info.onBackPressed(legislator_info.java:466)
at com.app.congress.congressapp.legislator_info.onOptionsItemSelected(legislator_info.java:454)
at android.app.Activity.onMenuItemSelected(Activity.java:2912)
at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:361)
at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:147)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:100)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:100)
at android.support.v7.widget.ToolbarWidgetWrapper$1.onClick(ToolbarWidgetWrapper.java:194)
at android.view.View.performClick(View.java:5201)
at android.view.View$PerformClick.run(View.java:21163)
at android.os.Handler.handleCallback(Handler.java:746)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
有人能告诉我为什么会出现上述错误以及如何修复它吗?super.onBackPressed()代码>调用将销毁/完成您的活动,您不能再使用属于此活动的任何对象,因此只需在末尾移动此调用,无需调用finish()
改变这个
final SharedPreferences pref = this.getContext().getSharedPreferences("MyFav", 0);
对此
final SharedPreferences pref = getActivity().getSharedPreferences("MyFav", 0);
注意:更好的选择是使用静态方法创建一个实用程序类,该方法将保存您的首选项数据,所以只需将上下文和数据传递给实用程序类并将其保存到首选项
public class Util {
public static void saveData(Context context,int i ){
// your preference code , change parameters accordingly
}
}
从你的活动中可以这样称呼它
Util.saveData(this,5);
您不能调用newfavRegislator()
并期望它具有上下文
这似乎是一个活动或片段类。当您新建一个时,上下文不会附加,因此getContext()
返回null
如果您试图在返回时刷新其他视图,请使用onResume
方法error@Anirban尝试更新,您应该使用getActivity()
函数来检索附加活动的上下文
public class Util {
public static void saveData(Context context,int i ){
// your preference code , change parameters accordingly
}
}
Util.saveData(this,5);