小编R3M*_*MIX的帖子

我一直在这行上得到NullPointerException:

SharedPreferences myPreference = PreferenceManager.getDefaultSharedPreferences(this);

我运行了一些东西,我相信我有错误的上下文,因为它在主包的子包中,所以我不认为它可以引用XML首选项文件.我已经在主程序包中的类中使用了这个,没有任何问题,但由于某种原因,这会导致异常.

完整代码:

package schoolBook.Icestone.Expandable;

import schoolBook.Icestone.Days;
import schoolBook.Icestone.Main;
import schoolBook.Icestone.SetPreference;
import android.content.SharedPreferences;
import android.preference.PreferenceManager;

public class Lesson1 extends Lessons {

    public Lesson1(String name) {
        super(name);
        // setGroup(" " + Days.getLessonarray(0) + " ");
        String key = "W" + Main.getWeek() + "_" + SetPreference.xmlday + "_L"
                + SetPreference.xmllesson + "_Lesson";
        System.out.println(key);
        try {
            SharedPreferences myPreference = PreferenceManager
                    .getDefaultSharedPreferences(this);
            String group = myPreference.getString(key, "def");
            setGroup(" " + group + " ");
        } catch (NullPointerException ex) {
            ex.printStackTrace(); …