所以我正在构建一个警报应用程序。我想在首次安装应用程序时显示一些默认警报。例如,上午 7 点、上午 8 点和上午 9 点有 3 个闹钟。下面是我的代码。
调用getAllAlarms()
来检索要显示的警报列表。第一次加载时,数据库将为空,因此我想插入一些默认值(如果是这种情况)。这可以在 else
语句中看到,我在其中添加警报,然后对其自身进行递归调用。我的理解是,添加3个闹钟后,我再次调用getAllAlarms
,它应该正常进入if语句。从调试 System.out.println
语句中可以看出,情况确实如此。警报列表按预期打印出来,但是,在该行的某个地方似乎再次调用了该方法,这导致列表被清空,如最后的调试语句中所示。
你能看出问题出在哪里吗?我已经在项目中进行了文件搜索,并且除了方法本身和 ListActivity
内部之外,我没有在任何地方调用删除方法,也没有调用 getAllAlarms
。我认为问题必须集中在 getAllAlarms
方法中,但我找不到它。是递归调用吗?
// Getting All Alarms
public List<Alarm> getAllAlarms() {
List<Alarm> alarmList = new ArrayList<Alarm>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_ALARMS;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Alarm alarm = new Alarm();
alarm.setID(cursor.getInt(0));
alarm.setHour(cursor.getInt(1));
alarm.setMinutes(cursor.getInt(2));
// Adding alarm to list
alarmList.add(alarm);
System.out.println("inside loop");
System.out.println(alarmList);
} while (cursor.moveToNext());
}
else
{
System.out.println("Adding default values...");
addAlarm(new Alarm(7,0));
addAlarm(new Alarm(8,0));
addAlarm(new Alarm(9,0));
System.out.println("Finished adding default values...");
getAllAlarms();
}
System.out.println("before");
System.out.println(alarmList);
System.out.println("after");
// return alarm list
return alarmList;
}
这是我的添加方法:
void addAlarm(Alarm alarm) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_HOUR, alarm.getHour()); // Alarm Name
values.put(KEY_MINUTES, alarm.getMinutes()); // Alarm Phone
// Inserting Row
db.insert(TABLE_ALARMS, null, values);
db.close(); // Closing database connection
}
调试输出:
04-23 16:17:49.261: I/System.out(10938): Adding default values...
04-23 16:17:49.291: I/System.out(10938): Finished adding default values...
04-23 16:17:49.291: I/System.out(10938): inside loop
04-23 16:17:49.291: I/System.out(10938): [07:00]
04-23 16:17:49.296: I/System.out(10938): inside loop
04-23 16:17:49.296: I/System.out(10938): [07:00, 08:00]
04-23 16:17:49.296: I/System.out(10938): inside loop
04-23 16:17:49.296: I/System.out(10938): [07:00, 08:00, 09:00]
04-23 16:17:49.296: I/System.out(10938): before
04-23 16:17:49.296: I/System.out(10938): [07:00, 08:00, 09:00]
04-23 16:17:49.296: I/System.out(10938): after
04-23 16:17:49.296: I/System.out(10938): before
04-23 16:17:49.296: I/System.out(10938): []
04-23 16:17:49.296: I/System.out(10938): after
更新::
我已经尝试过,但没有成功:
if (cursor.moveToFirst()) { 做 { 警报alarm = new Alarm(); Alarm.setID(cursor.getInt(0)); Alarm.setHour(cursor.getInt(1)); Alarm.setMinutes(cursor.getInt(2)); //将警报添加到列表中 AlarmList.add(警报); System.out.println("内部循环"); System.out.println(alarmList);
} while (cursor.moveToNext());
}
else
{
System.out.println("Adding default values...");
addAlarm(new Alarm(7,0));
addAlarm(new Alarm(8,0));
addAlarm(new Alarm(9,0));
System.out.println("Finished adding default values...");
}
if(alarmList.isEmpty() || alarmList == null)
{
System.out.println("test" + alarmList);
getAllAlarms();
}
但是,如果我删除 if 语句来检查空列表,然后将检查添加到数据库外部和 ListActivity
内部,则此操作会自行起作用。但这不是我想要的。我不想在数据库类之外处理默认值插入。
其他
{
System.out.println("添加默认值...");
addAlarm(新警报(7,0));
addAlarm(新警报(8,0));
addAlarm(新警报(9,0));
System.out.println("默认值添加完成...");
}
以及ListActivity
内部:
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_alarm_list);
Database db = new Database(AlarmListActivity.this);
list = db.getAllAlarms();
if(list.isEmpty())
{
list = db.getAllAlarms();
}
....
....
}
最佳答案
正如@umesh建议的那样,使用 getReadableDatabase(),不需要 db.close(),但最重要的是将您的写入包装在事务中:
db.beginTransaction();
// insert
db.setTransactionSuccessful();
db.endTransaction();
更新:单例(ish)模式
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBOpenHelper extends SQLiteOpenHelper {
private enum OpenHelperEnum {
INSTANCE; // Singleton instance;
// Instance of dbHelper for all DB access in threads
private SQLiteOpenHelper dbHelper = null;
private SQLiteDatabase database = null;
public SQLiteDatabase getDB(final Context context) {
if (dbHelper == null) {
dbHelper = new DBOpenHelper(context);
}
if (database == null) {
database = dbHelper.getReadableDatabase();
}
return database;
}
}
public DBOpenHelper(final Context context) {
super(context, "DBName", null, 1);
}
@Override
public void onCreate(final SQLiteDatabase database) {
// ...
}
@Override
public void onUpgrade(final SQLiteDatabase database, final int oldVersion, final int newVersion) {
// ...
}
@Override
public void onDowngrade(final SQLiteDatabase database, final int oldVersion, final int newVersion) {
// ...
}
public static SQLiteDatabase getDB(final Context context) {
return DBOpenHelper.OpenHelperEnum.INSTANCE.getDB(context);
}
}
要获取数据库,请使用:
final SQLiteDatabase db = DBOpenHelper.getDB(this);
关于java - 为什么我无法在 Android 的 SQLite 数据库中添加这些默认值?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/16173196/