我无法在 android 上执行我的 SQLite 应用程序。出于测试目的，我使它尽可能简单。将数据添加到数据库中的查询，当用户单击“查看计划”按钮时，数据库中的所有数据都应显示为 TOAST 消息。“MySQLitehelper.java”文件包含所有与数据库相关的代码，“SelectOptions.java”包含带有“查看计划”按钮的代码。所有正确的导入都已添加，因此我在这里省略了它们。
在 Tracing LogCat 中，我看到调用 MySQLitehelper 类的 helper.open() 方法时出现空指针异常。我尝试打印语句来跟踪它，并发现程序关闭了以下几行：
public MySQLitehelper open() throws SQLException
{
System.out.println("Inside open function");
db = dbhelper.getReadableDatabase(); // even tried helper.getWritableDatabase()
return this;
}
并在线路停止时
db = dbhelper.getReadableDatabase();
遇到。这是我的代码：
/* --------------MySQLitehelper.java 代码 -----*/
public class MySQLitehelper {
//public static final String TABLE_COMMENTS = "comments";
public static final String COLUMN_ID = "GWid";
public static final String COLUMN_DATE = "date";
public static final String COLUMN_LOCATION = "location";
public static final String COLUMN_TIME = "time";
public static final String TABLE_NAME = "UPDTable";
private static final String DATABASE_NAME = "UPDdb";
private static final int DATABASE_VERSION = 1;
private final Context context;
// Database creation sql statement
private static final String DATABASE_CREATE = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME +
" (" +COLUMN_ID+ " VARCHAR," + COLUMN_DATE + "VARCHAR," +
COLUMN_LOCATION+" VARCHAR," +COLUMN_TIME +" VARCHAR);";
private static final String DATABASE_INSERT = "INSERT INTO " +TABLE_NAME +
" Values ('47688507','DEC-07-2012','MARVIN 203','20:00');";
DatabaseHelper dbhelper;
SQLiteDatabase db;
public MySQLitehelper(Context ctx)
{
this.context = ctx;
}
private static class DatabaseHelper extends SQLiteOpenHelper {
public DatabaseHelper(Context context)
{
super(context,DATABASE_NAME, null,DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(DATABASE_CREATE); //execute create table
db.execSQL(DATABASE_INSERT); //execute insert query
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
Log.w(MySQLitehelper.class.getName(),
"Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
}
// open the DB
public MySQLitehelper open() throws SQLException
{
System.out.println("Inside open function");
db = dbhelper.getReadableDatabase();
return this;
}
public void close()
{
dbhelper.close();
}
public Cursor getAllrows() //function to get all rows in the DB. Testing initially.
{
//SQLiteDatabase db=this.getReadableDatabase();
Cursor cur=db.query(TABLE_NAME,new String []{COLUMN_ID, COLUMN_DATE,
COLUMN_LOCATION,COLUMN_TIME},null,null,null,null, null);
return cur;
}
}
/ ------------- SelectOptions.java 类 ------------------ /
public class SelectOptions extends Activity {
Button btnView, btnDrop, btnLocation;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_select_options);
Intent intent = getIntent();
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
btnView = (Button)findViewById(R.id.btnViewShift);
btnDrop = (Button)findViewById(R.id.btnDropShift);
btnLocation = (Button)findViewById(R.id.btnViewLocation);
final MySQLitehelper helper = new MySQLitehelper(this);
btnView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
helper.open();
Cursor c = helper.getAllrows();
if (c.moveToFirst()) {
do {
System.out.println("In Do while");
DisplayRecord(c);
} while (c.moveToNext());
}
helper.close();
System.out.println("Out of Do");
}
});
}
public void DisplayRecord(Cursor c)
{
System.out.println("In side toast display function");
Toast.makeText(this, "id: "+c.getString(0)+"\n"+
"Date: "+c.getString(1)+"\n"+
"Location: "+c.getString(2)+"\n"+
"Time: "+c.getString(3), Toast.LENGTH_LONG).show();
}
}
日志猫
11-29 06:18:01.393: I/System.out(8162): Inside open function
11-29 06:18:01.453: E/SQLiteLog(8162): (1) no such column: date
11-29 06:18:01.453: D/AndroidRuntime(8162): Shutting down VM
11-29 06:18:01.463: W/dalvikvm(8162): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
11-29 06:18:01.503: E/AndroidRuntime(8162): FATAL EXCEPTION: main
11-29 06:18:01.503: E/AndroidRuntime(8162): android.database.sqlite.SQLiteException: no such column: date (code 1): , while compiling: SELECT GWid, date, location, time FROM UPDTable
11-29 06:18:01.503: E/AndroidRuntime(8162): at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
11-29 06:18:01.503: E/AndroidRuntime(8162): at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882)
11-29 06:18:01.503: E/AndroidRuntime(8162): at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:493)
11-29 06:18:01.503: E/AndroidRuntime(8162): at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
11-29 06:18:01.503: E/AndroidRuntime(8162): at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
11-29 06:18:01.503: E/AndroidRuntime(8162): at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
11-29 06:18:01.503: E/AndroidRuntime(8162): at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)