我在使用SQLite并在我的Android应用程序中创建数据库时遇到问题。我希望有人在这里可以指出我只是在创建数据库时做错了。这是代码：
在DBContract类中：
public final class DBContract {
public DBContract() { }
public static abstract class DBEntry implements BaseColumns {
public static final String TABLE_WORKOUTS = "Workouts";
public static final String ENTRY_ID = "id";
public static final String ENTRY_NAME = "Exercise";
public static final String ENTRY_DESCRIPTION = "Description";
public static final String ENTRY_SETS = "Sets";
public static final String ENTRY_REPS = "Reps";
public static final String ENTRY_WEIGHT = "Weight";
}
private static final String TEXT_TYPE = "TEXT";
private static final String COMMA_SEP = ",";
private static final String SQL_CREATE_ENTRIES =
"CREATE TABLE " + DBEntry.TABLE_WORKOUTS + " (" +
DBEntry.ENTRY_ID + " INTEGER PRIMARY KEY," +
DBEntry.ENTRY_NAME + TEXT_TYPE + COMMA_SEP +
DBEntry.ENTRY_DESCRIPTION + TEXT_TYPE + COMMA_SEP +
DBEntry.ENTRY_SETS + TEXT_TYPE + COMMA_SEP +
DBEntry.ENTRY_REPS + TEXT_TYPE + COMMA_SEP +
DBEntry.ENTRY_WEIGHT + TEXT_TYPE + " )";
private static final String SQL_DELETE_ENTRIES =
"DROP TABLE IF EXISTS " + DBEntry.TABLE_WORKOUTS;
public static class DBHelper extends SQLiteOpenHelper {
public static final int DATABASE_VERSION = 1;
public static final String DATABASE_NAME = "DigiBottle.db";
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
db.execSQL(SQL_CREATE_ENTRIES);
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// This database is only a cache for online data, so its upgrade policy is
// to simply to discard the data and start over
db.execSQL(SQL_DELETE_ENTRIES);
onCreate(db);
}
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
onUpgrade(db, oldVersion, newVersion);
}
}
}
这就是我尝试访问数据库的方法：
public class MainActivity extends AppCompatActivity {
private BluetoothAdapter mBluetoothAdapter;
private BroadcastReceiver mReceiver;
private BluetoothSocket mmSocket;
private static int REQUEST_ENABLE_BT = 1;
private int hc05Index;
private String hc05Address;
private int numOfReadBytes;
private int readBuffer;
private ArrayList<String> deviceNameList = new ArrayList<String>();
private ArrayList<String> deviceAddressList = new ArrayList<String>();
DBContract.DBHelper mDBHelper = new DBContract.DBHelper(getBaseContext());
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
SQLiteDatabase db = mDBHelper.getWritableDatabase();
注意：我切断了主活动的onCreate（）函数的其余部分，以便不添加必须滚动的不必要的代码。
因此在Main Activity中我创建了一个我的DBHelper类的实例，并在main活动的onCreate函数内部调用getWriteableDatabase（）函数来获取现有数据库或创建一个新数据库（如果尚未创建） 。我的理解是这个函数将调用我的DBHelper类的onCreate（）函数，它应该执行写入的Create Table SQL Command并创建数据库。由于某种原因，getWriteableDatabase（）函数强制关闭应用程序。
非常感谢任何帮助！
提前致谢!!
编辑：这是日志：
02-01 22:04:48.681 21782-21782/com.example.rpholmes.digibottle E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.rpholmes.digibottle, PID: 21782
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.rpholmes.digibottle/com.example.rpholmes.digibottle.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:223)
at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
at com.example.rpholmes.digibottle.MainActivity.onCreate(MainActivity.java:45)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
02-01 22：04：48.705 21782-21782 /？ I /处理：发送信号。 PID：21782 SIG：9
答案 0 :(得分：0)
SQL查询需要适当的空格。
将DBContract中的以下行修改为...
private static final String TEXT_TYPE = " TEXT ";
private static final String COMMA_SEP = ", ";
（如果错误仍然存在，请发布您的日志语句）
答案 1 :(得分：0)
您试图在创建表之前插入值，尝试添加SQLiteDatabase db = mDBHelper.getWritableDatabase（）;仅在DBHelper类中。 这样在创建表插入后就可以完成了。
public void InsertValues(){
db =this.getWritableDatabase();
ContentValues cv = new ContentValues();
cv.put(DBEntry.ENTRY_NAME,"adc");
}