如何将应用程序上下文从 Singleton 类传递到 SharedPreferences?我在其 onActivityCreated(Bundle savedInstanceState) 方法中有一个 fragment 和一个 GridView,单击项目时,我在 logcat 中收到 NullPointerException:
03-30 05:12:54.784: E/AndroidRuntime(1950): FATAL EXCEPTION: main
03-30 05:12:54.784: E/AndroidRuntime(1950): java.lang.NullPointerException
03-30 05:12:54.784: E/AndroidRuntime(1950): at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:374)
03-30 05:12:54.784: E/AndroidRuntime(1950): at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:369)
03-30 05:12:54.784: E/AndroidRuntime(1950): at com.example.duaapp.utility.SharedPreferencesSupplication.save(SharedPreferencesSupplication.java:35)
单例类
public class SingletonClass {
public static Context applicationContext;
public static int fontSizeMin = 17;
public static int fontSizeMax = 35;
public static final String keySelVerseFromList = "keySelVerseFromList";
public static final String keyFavVerses = "keyFavVerses";
public static final String keyListOfVerses = "keyListOfVerses";
public static final String keyIsFavSelected = "keyIsFavSelected";
}
共享首选项
public class SharedPreferencesSupplication {
public void save(String valueKey, String value) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(SingletonClass.applicationContext);
SharedPreferences.Editor edit = prefs.edit();
edit.putString(valueKey, value);
edit.commit();
}
public void save(String valueKey, int value) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(SingletonClass.applicationContext);
SharedPreferences.Editor edit = prefs.edit();
edit.putInt(valueKey, value);
edit.commit();
}
public void save(String valueKey, boolean value) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(SingletonClass.applicationContext);
SharedPreferences.Editor edit = prefs.edit();
edit.putBoolean(valueKey, value);
edit.commit();
}
public void save(String valueKey, long value) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(SingletonClass.applicationContext);
SharedPreferences.Editor edit = prefs.edit();
edit.putLong(valueKey, value);
edit.commit();
}
}
在 gridview_item_Click 上,每当调用 new SharedPreferencesSupplication().save(SingletonClass.keyIsFavSelected, false); 时,应用程序崩溃并在 logcat 中引发空指针异常。我哪里错了?
切勿在 Android 中使用对 Context 的静态引用,这将导致重要的内存泄漏,因为 Context 引用了所有应用程序资源。
大多数 Android UI 类都有对上下文的动态引用,在 fragment 中你可以执行 getActivity()
,在 View 中 getContext()
考虑使用那些而不是上下文单例
有关此的更多信息 here
我是一名优秀的程序员,十分优秀!