java - Android FileoutputStream 空指针异常

Question

public class database_wrapper {
      users_database u_db;
      SQLiteDatabase sql_db;
     Context context;

    database_wrapper(Context context)
    {
        u_db = new users_database(context);
        sql_db = u_db.getWritableDatabase();
    }

    public long insert_data(List<name_holder> list)
    {
        ContentValues contentValues = new ContentValues();

        long error_code = 0;
        String fileName;
        for(int i = 0; i < list.size(); i++) {
            fileName = "test_image";//String.valueOf(list.get(i).id);
            Log.v("datadata",fileName);
            if(list.get(i)._bmp == null)
            {
                Log.v("datadata", "no image");
            }
            try {
                ByteArrayOutputStream bytes = new ByteArrayOutputStream();
                FileOutputStream fo;
                list.get(i)._bmp.compress(Bitmap.CompressFormat.JPEG, 100, bytes);
                fo = context.openFileOutput(fileName, context.MODE_PRIVATE);

                fo.write(bytes.toByteArray());
                // remember close file output
                fo.close();
            } catch (Exception e) {
                e.printStackTrace();
                Log.v("datadata", e.toString());
                fileName = "null";
            }

            contentValues.put(u_db.ID, list.get(i).id);
            Log.v("datadata1", String.valueOf(list.get(i).id));
            contentValues.put(u_db.NAME, list.get(i).name);
            Log.v("datadata2", list.get(i).name);
            contentValues.put(u_db.DISTANCE, list.get(i).distance);
            Log.v("datadata3", String.valueOf(list.get(i).distance));
            contentValues.put(u_db.AVATAR, fileName);
            Log.v("datadata4", fileName);
            contentValues.put(u_db.AGE, list.get(i).age);
            Log.v("datadata5", list.get(i).age);
            contentValues.put(u_db.SEX, list.get(i).sex);
            Log.v("datadata6", list.get(i).sex);
            contentValues.put(u_db.ORIENT, list.get(i).orient);
            Log.v("datadata7", String.valueOf(list.get(i).orient));

            long j = sql_db.insert(u_db.TABLE_NAME, null, contentValues);
            if (j < 0)
                error_code = j;

            int y = (int)j;
            Log.v("datadata", String.valueOf(y));
        }
        return error_code;
    }

这段代码给了我这个异常(exception): java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“java.io.FileOutputStream android.content.Context.openFileOutput(java.lang.String, int)” 我需要帮助..我做错了什么？ 第一次迭代的 LogCat:

07-23 06:45:56.686    8796-8915/? V/datadata﹕ test_image
07-23 06:45:56.696    8796-8915/? V/datadata﹕ java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.FileOutputStream android.content.Context.openFileOutput(java.lang.String, int)' on a null object reference
07-23 06:45:56.696    8796-8915/? V/datadata1﹕ 2
07-23 06:45:56.696    8796-8915/? V/datadata2﹕ `h jvkv H  h r
07-23 06:45:56.696    8796-8915/? V/datadata3﹕ 0
07-23 06:45:56.696    8796-8915/? V/datadata4﹕ null
07-23 06:45:56.696    8796-8915/? V/datadata5﹕ 90
07-23 06:45:56.696    8796-8915/? V/datadata6﹕ Male
07-23 06:45:56.696    8796-8915/? V/datadata7﹕ 0
07-23 06:45:56.706    8796-8915/? V/datadata﹕ -1

Answer 1

您没有初始化 context 对象，这就是您得到 NullPointerException 的原因。

在 database_wrapper() 构造方法中初始化 context 对象。

database_wrapper(Context context) {

    this.context = context;

    u_db = new users_database(context);
    sql_db = u_db.getWritableDatabase();
}