正如标题所述,我遇到了 NullPointerException
,它发生在以下方法的第一个 getString()
处。为了调试,我使用 DatabaseUtils.dumpCursorToString() 来查看光标,并且光标内有值,但在 if 语句和 do 语句之间声明,有些事情发生了变化。我在单独 Activity 的另一种方法中使用了相同的代码,并且它工作完美。
public ArrayList<String> getMusic() {
helper = new DbHelper(context);
db = helper.getReadableDatabase();
String[] cols = new String[]{MUSIC_ID, MUSIC_COUNTRY, MUSIC_BLUES, MUSIC_ROCK, MUSIC_METAL,
MUSIC_HIPHOP, MUSIC_CLASSICAL, MUSIC_PUNK, MUSIC_TECHNO, MUSIC_JAZZ, MUSIC_OTHER};
Cursor c = db.query(TABLE_MUSIC_INT, cols, null, null, null, null, null);
int count = c.getCount();
Log.v("INTEREST CURSOR ", "Count: " + count); // log row count
if (c.moveToFirst()) {
Log.v("INTEREST CURSOR ", DatabaseUtils.dumpCursorToString(c)); // dump cursor values
do {
musicInt.add(c.getString(0));
musicInt.add(c.getString(1));
musicInt.add(c.getString(2));
musicInt.add(c.getString(3));
musicInt.add(c.getString(4));
musicInt.add(c.getString(5));
musicInt.add(c.getString(6));
musicInt.add(c.getString(7));
musicInt.add(c.getString(8));
musicInt.add(c.getString(9));
musicInt.add(c.getString(10));
} while (c.moveToNext());
} else {
Log.e("DB_GET_DATA ", " DB_GET_DATA == null");
}
c.close();
return musicInt;
}
DatabaseUtils.dumpCursorToString(c) 输出:
01-15 19:57:01.201 6247-6247/us.enyi.enyi D/DB OPEN READ: Successful
01-15 19:57:20.440 6247-6247/us.enyi.enyi V/INTEREST CURSOR: Count: 1
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@2f32900f
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: 0 {
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: _id=1
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: country=null
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: blues=null
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: rock=Rock
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: metal=Metal
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: hiphop=HipHop
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: classical=Classical
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: punk=null
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: techno=Techno
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: jazz=null
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: musicother=Other
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: }
01-15 19:57:27.897 6247-6247/us.enyi.enyi V/INTEREST CURSOR: <<<<<
我尝试过其他从游标检索数据的方法,并在 SO 和 Android Docs 中阅读了无数线程,但没有找到任何有用的解决方案。我不太明白为什么光标显然有值,但 c.getString() 在 NPE 上失败。任何帮助将不胜感激。
解决方案:
初始化musicInt失败导致Cursor无处放置其收集的数据。将 musicInt 声明为:
ArrayList<String> musicInt;
而不是:
ArrayList<String> musicInt = new ArrayList<>();
教训是确保正确初始化变量。你会像我一样把头发拔掉。
最佳答案
我没有看到你在哪里声明(或初始化)musicInt
。这可能就是导致您出现 NPE 的原因。
关于java - Android Cursor NPE dumpCursorToString 返回值,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/34823361/