从sqlite数据库中提取一些数据并将其传递给另一个类后,我无法诊断错误。我认为过关是我遇到问题的地方。
事实:我的数据库充满了以下格式的数据:
1447206226445|1
1447206228288|0
1447206462437|1
(第一列是长,第二列是整数)
在我的主要课程中,我试图在数据库中搜索一系列长值,并相应地显示内容。我用:
Days[] daysList = dbHandler.findRange(first.getTimeInMillis(), last.getTimeInMillis());
获取我想要的日期列表,其中 first 和 last 是Calendar对象。
然后我使用:
for (int i = 0; i < 7; i++) {
for (int j = 0; j < daysList.length; j++) {
if (daysList[j].getID() > first.getTimeInMillis() && daysList[j].getID() < second.getTimeInMillis()) {
...
...
...
对daysList中的数据进行排序。但是,我在这里收到以下错误:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long com.example.william.timeclockr.Days.getID()' on a null object reference
这是我的DBHandler findRange()方法:
public Days[] findRange(long startRange, long endRange) {
String query = "Select * FROM " + TABLE_DAYS + " WHERE " + COLUMN_DAYSLONG + " >= " + startRange + " AND " + COLUMN_DAYSLONG + " <= " + endRange + ";";
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(query, null);
Days day = new Days();
Days[] days = new Days[cursor.getCount()];
int i = 0;
cursor.moveToFirst();
do {
//while (cursor.moveToNext()) {
day.setID(cursor.getLong(0));
day.setStatus(cursor.getInt(1));
days[i] = day;
i++;
cursor.moveToNext();
//}
} while (cursor.moveToNext());
cursor.close();
db.close();
return days;
}
这是我的Days课程:
package com.example.william.timeclockr;
public class Days {
private long _id;
private int _status;
public Days() {
}
public Days(long id, int status) {
this._id = id;
this._status = status;
}
public Days(int status) {
this._status = status;
}
public void setID(long id) {
this._id = id;
}
public long getID() {
return this._id;
}
public void setStatus(int status) {
this._status = status;
}
public int getStatus() {
return this._status;
}
}
我知道这是一个很多信息,但是我觉得我正在犯这样一个错误的错误传递这个列表,有什么帮助吗?
答案 0 :(得分:1)
问题似乎出现在do-while
方法的findRange()
循环中。每次循环时都需要实例化一个新的Days
对象。此外,您每次都要调用cursor.moveToNext();
两次,这比数组索引更快地推进Cursor
,导致最终NullPointerException
。
do {
day = new Days();
day.setID(cursor.getLong(0));
day.setStatus(cursor.getInt(1));
days[i] = day;
i++;
} while (cursor.moveToNext());