一般来说，我是应用程序开发、Android 和内部数据库的新手。我需要编写一个包含字符串的简单数据库，并在屏幕上按下按钮来显示字符串以进行演示。演示中最重要的部分是内部数据库。我似乎找不到关于如何为 Android 应用编写教程的好教程。任何人都可以帮忙吗？
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515 次
1 回答
1
您将需要一个带有数据库助手的数据库适配器。适配器将处理您的数据访问，助手将处理打开、创建和升级。这是代码项目的一篇文章：
下面是一个使用数据库适配器和助手的例子：
public void loadList() {
String title = "";
arrayAdapter.clear();
DaysDatabaseAdapter dbAdapter = new DaysDatabaseAdapter(getApplicationContext());
dbAdapter.open();
Cursor c = dbAdapter.getAllRows();
if (c.moveToFirst()) {
do {
title = c.getString(DaysDatabaseAdapter.POS_TITLE);
arrayAdapter.add(title);
} while (c.moveToNext());
}
c.close();
dbAdapter.close();
}
下面是我的一个项目中的一个数据库适配器。它是旧的，我现在有更好的技术，但它有效。
公共类 DaysDatabaseAdapter {
// 全局变量
public static final String TAG = "DaysDBAdapter";
public static final String COLUMN_ROWID = "_id";
public static final String COLUMN_INUSE = "inuse";
public static final String COLUMN_TITLE = "title";
public static final String COLUMN_YEAR = "year";
public static final String COLUMN_MONTH = "month";
public static final String COLUMN_DAY = "day";
public static final String[] COLUMN_NAMES = {
COLUMN_ROWID, COLUMN_INUSE, COLUMN_TITLE, COLUMN_YEAR, COLUMN_MONTH, COLUMN_DAY
};
public static final String[] COLUMN_NAMES_NO_ROWID = {
COLUMN_INUSE, COLUMN_TITLE, COLUMN_YEAR, COLUMN_MONTH, COLUMN_DAY
};
public static final int POS_ROWID = 0;
public static final int POS_INUSE = 1;
public static final int POS_TITLE = 2;
public static final int POS_YEAR = 3;
public static final int POS_MONTH = 4;
public static final int POS_DAY = 5;
private static final String DATABASE_NAME = "daystildayssince";
private static final String DATABASE_TABLE = "days";
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE = "create table " + DATABASE_TABLE
+ " ("
+ COLUMN_ROWID + " integer primary key autoincrement, "
+ COLUMN_INUSE + " integer not null, "
+ COLUMN_TITLE + " text not null, "
+ COLUMN_YEAR + " integer not null, "
+ COLUMN_MONTH + " integer not null, "
+ COLUMN_DAY + " integer not null"
+ ");";
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
// ******************* Functions ***************************
// Constructor
public DaysDatabaseAdapter(Context ctx) {
MyLog.d(TAG, "Adapter Constructor entered");
DBHelper = new DatabaseHelper(ctx);
}
// Open the database
public DaysDatabaseAdapter open() throws SQLException {
MyLog.d(TAG, "open database");
db = DBHelper.getWritableDatabase();
return this;
}
// Close the database
public void close() {
MyLog.d(TAG, "close database");
DBHelper.close();
}
// Insert row
public long insertRow(int inuse, String title, int year, int month, int day) {
MyLog.d(TAG, "insertRow");
initialValues.put(COLUMN_INUSE, inuse);
initialValues.put(COLUMN_TITLE, title);
initialValues.put(COLUMN_YEAR, year);
initialValues.put(COLUMN_MONTH, month);
initialValues.put(COLUMN_DAY, day);
return db.insert(DATABASE_TABLE, null, initialValues);
}
// Delete row using COLUMN_ROWID
public boolean deleteRow(long rowid) {
MyLog.d(TAG, "delete row " + Long.toString(rowid));
return db.delete(DATABASE_TABLE, COLUMN_ROWID + " = " + Long.toString(rowid), null) > 0;
}
// Get all rows
public Cursor getAllRows() {
MyLog.d(TAG, "getAllRows");
return db.query(DATABASE_TABLE, COLUMN_NAMES, null, null, null, null, null);
}
// Get specific row using COLUMN_ROWID (primary key)
public Cursor getRowByKey(long rowid) throws SQLException {
MyLog.d(TAG, "getRowByKey");
Cursor mCursor = db.query(true, DATABASE_TABLE, COLUMN_NAMES, COLUMN_ROWID + " = " + Long.toString(rowid), null,
null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
// Get all rows that match COLUMN_INUSE (the Widget AppWidgetId used for the match.)
public Cursor getInuseMatches(int appWidgetId) throws SQLException {
MyLog.d(TAG, "getInuseMatches");
Cursor mCursor = db.query(DATABASE_TABLE,
COLUMN_NAMES, COLUMN_INUSE + " = " + Integer.toString(appWidgetId),
null, null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
// Get row(s) that match title
public Cursor getTitleMatches(String title) throws SQLException {
MyLog.d(TAG, "TitleMatches");
String where[] = {title};
Cursor mCursor = db.query(DATABASE_TABLE,
COLUMN_NAMES, COLUMN_TITLE + " = ?",
where, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
// Turn off COLUMN_INUSE in matching rows
public boolean setUnused(int inuse) {
MyLog.d(TAG, "Adapter setUnused");
ContentValues contentValues = new ContentValues();
contentValues.put(COLUMN_INUSE, 0);
return db.update(DATABASE_TABLE, contentValues, COLUMN_INUSE + " = " + Integer.toString(inuse), null) > 0;
}
// Turn off COLUMN_INUSE in all rows
public boolean setAllUnused() {
MyLog.d(TAG, "Adapter setAllUnused");
ContentValues contentValues = new ContentValues();
contentValues.put(COLUMN_INUSE, 0);
return db.update(DATABASE_TABLE, contentValues, null, null) > 0;
}
// Set COLUMN_INUSE to Widget id using COLUMN_ROWID (primary key)
public boolean setInuse(long rowid, int inuse) {
MyLog.d(TAG, "setInuse (" + Long.toString(rowid) + ", " + Integer.toString(inuse) + ")");
ContentValues contentValues = new ContentValues();
contentValues.put(COLUMN_INUSE, inuse);
return db.update(DATABASE_TABLE, contentValues, COLUMN_ROWID + " = " + Long.toString(rowid), null) > 0;
}
// ***************** inline classes ***********************
// Database Helper Class
private static class DatabaseHelper extends SQLiteOpenHelper {
public static final String TAG = "DaysDBHelper";
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
MyLog.d(TAG, "Constructor");
}
@Override
public void onCreate(SQLiteDatabase db) {
MyLog.d(TAG, "Helper onCreate entered");
db.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
MyLog.w(TAG, "Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(db);
}
}
}
于 2012-09-25T03:28:34.937 回答