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android - 在第一次启动时创建 SQL 数据库并在下次启动时检索数据库数据

转载 作者:搜寻专家 更新时间:2023-10-30 20:30:55 24 4
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关于 android 开发,我只是想在 Activity 首次启动时(使用首选项)创建一个 SQL 数据库。第二次启动该 Activity 时,它应该从数据库中检索数据并输出一条日志消息。

我第一次设法启动了该 Activity (我假设数据库是在这里创建的)但是第二次我得到一个 IllegalStateException 错误:从第 0 行到第 -1 列的字段槽失败。不太确定我哪里出错了。有人可以检查吗?谢谢

主类

public class MainMenu extends Activity implements OnClickListener{
private ModulesDbAdapter mpDbHelper;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

//create database here
SharedPreferences initialPref = getSharedPreferences("INITIAL", 0);
boolean firsttimer = initialPref.getBoolean("INITIAL", false);

if (!firsttimer){
//create database here
mpDbHelper = new ModulesDbAdapter(this);
mpDbHelper.open();

long id1 = mpDbHelper.createReminder("Hello1", "Test 1", "Date1");
long id2 = mpDbHelper.createReminder("Hello2", "Test 2", "Date2");
long id3 = mpDbHelper.createReminder("Hello3", "Test 3", "Date3");

/*Cursor c = mpDbHelper.fetchModules((String)"CS118");
Log.d("TESTING",c.getString(c.getColumnIndex("KEY_MOD_NAME")));*/

//get boolean preference to true
SharedPreferences.Editor editorPref = initialPref.edit();
editorPref.putBoolean("INITIAL", true);
editorPref.commit();
}else {
fetchData();
}
}

private void fetchData(){
mpDbHelper = new ModulesDbAdapter(this);
mpDbHelper.open();
long input = 2;

Cursor c = mpDbHelper.fetchReminder(input);
startManagingCursor(c);
Log.d("TESTING",c.getString(c.getColumnIndex("KEY_BODY")));
}

/*@Override
protected void onPause() {
super.onPause();
mpDbHelper.close();
}

@Override
protected void onStop() {
super.onPause();
mpDbHelper.close();
}*/

}
}

适配器类

public class ModulesDbAdapter {
private static final String DATABASE_NAME = "data";
private static final String DATABASE_TABLE = "reminders";
private static final int DATABASE_VERSION = 1;

public static final String KEY_TITLE = "title";
public static final String KEY_BODY = "body";
public static final String KEY_DATE_TIME = "reminder_date_time";
public static final String KEY_ROWID = "_id";

private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;

//defines the create script for the database
private static final String DATABASE_CREATE =
"create table " + DATABASE_TABLE + " ("
+ KEY_ROWID + " integer primary key autoincrement, "
+ KEY_TITLE + " text not null, "
+ KEY_BODY + " text not null, "
+ KEY_DATE_TIME + " text not null);";

//Context object that will be associated with the SQLite database object
private final Context mCtx;

//The Context object is set via the constructor of the class
public ModulesDbAdapter(Context ctx) {
this.mCtx = ctx;
}

//helps with the creation and version management of the SQLite database.
private static class DatabaseHelper extends SQLiteOpenHelper {

//call made to the base SQLiteOpenHelper constructor. This call creates, opens, and/or manages a database
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,int newVersion) {
// Not used, but you could upgrade the database with ALTER
// Scripts
}
}

//now create the database by calling the getReadableDatabase()
public ModulesDbAdapter open() throws android.database.SQLException {
mDbHelper = new DatabaseHelper(mCtx);
mDb = mDbHelper.getWritableDatabase();
return this;
}

//close the database
public void close() {
mDbHelper.close();
}

public long createReminder(String title, String body, String
reminderDateTime) {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_TITLE, title);
initialValues.put(KEY_BODY, body);
initialValues.put(KEY_DATE_TIME, reminderDateTime);

//insert row into database
return mDb.insert(DATABASE_TABLE, null, initialValues);
}



public boolean deleteReminder(long rowId) {
return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}

//utilizes the query() method on the SQLite database to find all the reminders in the system
public Cursor fetchAllReminders() {
return mDb.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE,
KEY_BODY, KEY_DATE_TIME}, null, null, null, null, null);
}

public Cursor fetchReminder(long rowId) throws SQLException {
Cursor mCursor =
mDb.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
KEY_TITLE, KEY_BODY, KEY_DATE_TIME}, KEY_ROWID + "=" +
rowId, null, null, null, null, null);



if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}

public boolean updateReminder(long rowId, String title, String body, String reminderDateTime) {
ContentValues args = new ContentValues();
args.put(KEY_TITLE, title);
args.put(KEY_BODY, body);
args.put(KEY_DATE_TIME, reminderDateTime);
return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}
// The SQLiteOpenHelper class was omitted for brevity
// That code goes here.

最佳答案

错误很简单。您已在 DbAdapter 类中将 KEY_BODY 定义为静态字符串常量值,但您在访问代码中使用了字符串文字“KEY_BODY”。

Log.d("TESTING",c.getString(c.getColumnIndex("KEY_BODY")));

应该是

Log.d("TESTING",c.getString(c.getColumnIndex(ModulesDbAdapter.KEY_BODY)));

关于android - 在第一次启动时创建 SQL 数据库并在下次启动时检索数据库数据,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/8114131/

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