Question

我制作了一个PreferenceActivity来控制我的应用程序的设置。每次我点击一个偏好时，应用程序崩溃并产生NullPointerException错误。

这是PreferenceFragment：

public class SettingsFragment extends PreferenceFragment {

EditText enterPassword, newPassword;
public final String filename = "PasswordFile";
String myPassword;
static SharedPreferences myFolder;
public static String dataReturned = "";
Context context;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    addPreferencesFromResource(R.xml.preferences_new);

Preference password_pref = (Preference) findPreference("password");
password_pref.setOnPreferenceClickListener(new OnPreferenceClickListener() {

    public boolean onPreferenceClick(Preference preference) {
        // TODO Auto-generated method stub
        LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        final View text = inflater.inflate(R.layout.changepassword, null);
        final EditText currentPassword = (EditText)text.findViewById(R.id.currentPassword);
        final EditText newPassword = (EditText)text.findViewById(R.id.newPassword);

        final AlertDialog.Builder alert = new AlertDialog.Builder(context);
        alert.setTitle("Change Your Password");
        alert.setView(text);
        alert.setPositiveButton("Change", new DialogInterface.OnClickListener() {

            public void onClick(DialogInterface dialog, int which) {
                    String stringData = currentPassword.getText().toString().trim();
                    String stringNew = newPassword.getText().toString().trim();
                    dataReturned = myFolder.getString("passwordKey", "");
                    if(dataReturned.equals(stringData)) {                       
                        String newData = newPassword.getText().toString().trim();
                        SharedPreferences.Editor editor = myFolder.edit();
                        editor.putString("passwordKey", newData);
                        editor.commit();
                        dataReturned  = myFolder.getString("passwordKey", "couldn't load data");
                        Toast.makeText(context, "Password changed", Toast.LENGTH_SHORT).show();
                        currentPassword.setText("");
                        newPassword.setText("");
                    }

                    else {
                        Toast.makeText(context, "Incorrect Password", Toast.LENGTH_LONG).show();
                        currentPassword.setText("");
                        newPassword.setText("");
                    }
                }
            });
        alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {

            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub
                dialog.cancel();
            }
            });
        alert.show();
        ;

        return true;
    }

});

Preference notification_pref = (Preference) findPreference("notification");
notification_pref.setOnPreferenceClickListener(new OnPreferenceClickListener() {

    public boolean onPreferenceClick(Preference preference) {
        // TODO Auto-generated method stub
        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(context)
        .setSmallIcon(R.drawable.device_access_secure)
        .setOngoing(true)
        .setContentTitle("Obstruct")
        .setContentText("Start Stealth Mode");

        Intent resultIntent = new Intent();

        TaskStackBuilder stackBuilder = TaskStackBuilder.create(context);
        stackBuilder.addNextIntent(resultIntent);

        PendingIntent resultPendingIntent = stackBuilder.getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);
        mBuilder.setContentIntent(resultPendingIntent);

        NotificationManager mNotificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
        mNotificationManager.notify(0, mBuilder.build());
        return true;
    }

});
}
}

这是logcat：

11-23 15:23:36.191: E/AndroidRuntime(17168): FATAL EXCEPTION: main
11-23 15:23:36.191: E/AndroidRuntime(17168): java.lang.NullPointerException
11-23 15:23:36.191: E/AndroidRuntime(17168):    at com.mshaw.avanos8.adfree.SettingsFragment$1.onPreferenceClick(SettingsFragment.java:42)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.preference.Preference.performClick(Preference.java:941)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.preference.PreferenceScreen.onItemClick(PreferenceScreen.java:202)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.widget.AdapterView.performItemClick(AdapterView.java:292)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.widget.AbsListView.performItemClick(AbsListView.java:1071)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.widget.AbsListView$PerformClick.run(AbsListView.java:2527)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at  android.widget.AbsListView$1.run(AbsListView.java:3181)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.os.Handler.handleCallback(Handler.java:605)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.os.Handler.dispatchMessage(Handler.java:92)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.os.Looper.loop(Looper.java:154)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at android.app.ActivityThread.main(ActivityThread.java:4894)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at java.lang.reflect.Method.invokeNative(Native Method)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at java.lang.reflect.Method.invoke(Method.java:511)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
11-23 15:23:36.191: E/AndroidRuntime(17168):    at dalvik.system.NativeStart.main(Native Method)

我已经尝试了一切来解决这个问题。我怀疑上下文应该受到指责，但我不确定。

Answer 1

看起来您的变量上下文为null，尝试使用getActivity（）而不是上下文，或者通过在Preferencesfragment的构造函数中传递打开首选项的活动的上下文并将其分配给您的变量。

Answer 2

不是在类上定义context变量，而是在onCreate中将其定义为

final Context context = this;

Answer 3

请确保您放置＆＃34; addPreferencesFromResource＆＃34;在片段类中的getPreferenceScreen之前，例如：

{{1}}

PreferenceFragment：NullPointerException

3 个答案: