使用 Android 游标 db.query 从 SQLite 检索日期列答案

【问题标题】：Retrieve Date Column from SQLite Using Android Cursor db.query使用 Android 游标 db.query 从 SQLite 检索日期列
【发布时间】：2014-05-08 19:59:09
【问题描述】：

如何检索包含 SQLite TIMESTAMP 列的行并将这些列转换为 Android 中的 Java Date 类型参数。

我想使用 Android 游标 db.query 从 SQLite 数据库中检索行，这里是表定义

private final static String TABLE_NAME = "custTable";
private final static String COLUMN_ID = "_id";
private final static String COLUMN_NAME = "name";
private final static String COLUMN_EMAIL = "email";
private final static String COLUMN_PHONE = "phone";
private final static String COLUMN_UID = "card_uid2";
private final static String COLUMN_INITIAL_VALUE = "initial_value";
private final static String COLUMN_CURRENT_VALUE = "current_value";
private final static String COLUMN_DATE_CREATED = "enrollment_date";
private final static String COLUMN_LAST_UPDATED = "last_transaction_date";

这是我的游标 db.query 语句

Cursor cursor = database.query(TABLE_NAME, new String[]{ COLUMN_ID,COLUMN_NAME,COLUMN_EMAIL, COLUMN_PHONE +
                 COLUMN_UID, COLUMN_INITIAL_VALUE, COLUMN_CURRENT_VALUE,COLUMN_DATE_CREATED,COLUMN_LAST_UPDATED}, null, null, null, null, null);

如果我这样做，我如何将我的两个 SQLite Timestamp 列转换或转换为 Java Date 参数。经过多次尝试，我尝试像这样使用 cursor db.rawquery

Cursor cursor = database.rawQuery(
                "SELECT _id, name, email, phone, card_uid2, initial_value, current value," +
                 " (strftime('%s', enrollment_date) * 1000) AS enrollment_date, " +
                 " (strftime('%s', last_transaction_date) * 1000) AS last_transaction_date, +" +
                 "FROM  custTable", new String[0]);

使用 db.rawquery 选项，我继续更改为 Java Date 参数，例如

        long millis_enrolled = cursor.getLong(cursor.getColumnIndexOrThrow("enrollment_date"));
        Date enrolledDate = new Date(millis_enrolled);
        customer.setEnrollmentDate(enrolledDate);

        long millis_updated = cursor.getLong(cursor.getColumnIndexOrThrow("last_transaction_date"));
        Date updatedDate = new Date(millis_updated);
        customer.setEnrollmentDate(updatedDate);

无论哪种方式，当我尝试在我的 Activity 中访问这些值时，我都会收到类似的 Java NullPointerException

05-08 15:52:45.484: W/dalvikvm(1950): threadid=1: thread exiting with uncaught exception (group=0xb1f07648)
05-08 15:52:45.484: E/AndroidRuntime(1950): FATAL EXCEPTION: main
05-08 15:52:45.484: E/AndroidRuntime(1950): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.txsystems.valuecard/com.txsystems.valuecard.app.ReportActivity}: java.lang.NullPointerException
05-08 15:52:45.484: E/AndroidRuntime(1950):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
05-08 15:52:45.484: E/AndroidRuntime(1950):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
05-08 15:52:45.484: E/AndroidRuntime(1950):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-08 15:52:45.484: E/AndroidRuntime(1950):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
05-08 15:52:45.484: E/AndroidRuntime(1950):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-08 15:52:45.484: E/AndroidRuntime(1950):     at android.os.Looper.loop(Looper.java:137)
05-08 15:52:45.484: E/AndroidRuntime(1950):     at android.app.ActivityThread.main(ActivityThread.java:5103)
05-08 15:52:45.484: E/AndroidRuntime(1950):     at java.lang.reflect.Method.invokeNative(Native Method)

所以我的问题再次是如何检索包含 SQLite TIMESTAMP 列的行并将这些列转换为 Java Date 类型参数。

这里是创建表语句

private static final String CREATE_CUSTOMER_TABLE =
                "CREATE TABLE " + TABLE_NAME + "(" +
                COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "  +
                COLUMN_NAME + " TEXT NOT NULL, " +
                COLUMN_EMAIL + " TEXT, " +
                COLUMN_PHONE + " TEXT, " +
                COLUMN_UID + " TEXT, " +
                COLUMN_DATE_CREATED + " TIMESTAMP NOT NULL DEFAULT current_timestamp, " +
                COLUMN_LAST_UPDATED + " TIMESTAMP NOT NULL DEFAULT current_timestamp, " +
                COLUMN_INITIAL_VALUE + " NUMERIC, " +
                COLUMN_CURRENT_VALUE + " NUMERIC " +
                ")";

更多 Logcat 输出

05-08 17:12:46.857: I/Enrollment(2398): Calling the GetAll Customers method
05-08 17:12:46.857: I/Enrollment(2398): Inside getAllCustomer function
05-08 17:12:46.857: D/AndroidRuntime(2398): Shutting down VM
05-08 17:12:46.857: W/dalvikvm(2398): threadid=1: thread exiting with uncaught exception (group=0xb1f07648)
05-08 17:12:46.857: E/AndroidRuntime(2398): FATAL EXCEPTION: main
05-08 17:12:46.857: E/AndroidRuntime(2398): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.txsystems.valuecard/com.txsystems.valuecard.app.ReportActivity}: java.lang.NullPointerException
05-08 17:12:46.857: E/AndroidRuntime(2398):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)

【问题讨论】：

我建议你查看完整的堆栈跟踪，看看 NPE 在哪里。
我想我们需要看看create table语句。我不认为时间戳数据类型只是用于日期操作的函数。
我已经添加了 create table 语句，我可以使用 sqlite3 命令验证表已创建并且我正在向表中写入数据。
你能指出你得到 NPE 的那条线吗？
添加了更多显示 NPE 的 Logcat 输出，谢谢

标签： java android sqlite android-sqlite

【解决方案1】：

问题是数据库在我尝试在 Activity 中使用它之前没有打开，所以我在进行第一个数据库查询之前调用了db.getwritableDatabase()。

【讨论】：