Sqlite创建database的两种方法，以及源码分析，以及抽象类如何在SqliteHelper中应用

public class MyDbHelper extends SQLiteOpenHelper{

public MyDbHelper(Context context,int version) {
super(context, "testMusic1.db", null, version);
}
@Override
public void onCreate(SQLiteDatabase db) {

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion) {
}

}

注意还要用getWriteableDatabase或者是getReadableDatabase来获取db对象：

MyDbHelper dbHelper = new MyDbHelper(MainActivity.this,1);
SQLiteDatabase db = dbHelper.getWritableDatabase();

SQLiteDataBase源码分析从getWritableDatabase入手：

public SQLiteDatabase getWritableDatabase() {
synchronized (this) {
return getDatabaseLocked(true);
}
}

再是 getDatabaseLocked(true) --->
private SQLiteDatabase getDatabaseLocked(boolean writable) {
if (mDatabase != null) {
if (!mDatabase.isOpen()) {
// Darn!  The user closed the database by calling mDatabase.close().
mDatabase = null;
} else if (!writable || !mDatabase.isReadOnly()) {
// The database is already open for business.
return mDatabase;
}
}

if (mIsInitializing) {
throw new IllegalStateException("getDatabase called recursively");
}

SQLiteDatabase db = mDatabase;
try {
mIsInitializing = true;

if (db != null) {
if (writable && db.isReadOnly()) {
db.reopenReadWrite();
}
} else if (mName == null) {
db = SQLiteDatabase.create(null);
} else {
try {
if (DEBUG_STRICT_READONLY && !writable) {
final String path = mContext.getDatabasePath(mName).getPath();
db = SQLiteDatabase.openDatabase(path, mFactory,
SQLiteDatabase.OPEN_READONLY, mErrorHandler);
} else {
db = mContext.openOrCreateDatabase(mName, mEnableWriteAheadLogging ?
Context.MODE_ENABLE_WRITE_AHEAD_LOGGING : 0,
mFactory, mErrorHandler);
}
} catch (SQLiteException ex) {
if (writable) {
throw ex;
}
Log.e(TAG, "Couldn't open " + mName
+ " for writing (will try read-only):", ex);
final String path = mContext.getDatabasePath(mName).getPath();
db = SQLiteDatabase.openDatabase(path, mFactory,
SQLiteDatabase.OPEN_READONLY, mErrorHandler);
}
}

onConfigure(db);

final int version = db.getVersion();
if (version != mNewVersion) {
if (db.isReadOnly()) {
throw new SQLiteException("Can't upgrade read-only database from version "+ db.getVersion() + " to " + mNewVersion + ": " + mName);
}

db.beginTransaction();
try {
if (version == 0) {
onCreate(db); //抽象方法
} else {
if (version > mNewVersion) {
onDowngrade(db, version, mNewVersion);
} else {
onUpgrade(db, version, mNewVersion); //抽象方法
}
}
db.setVersion(mNewVersion);
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
}

onOpen(db);

if (db.isReadOnly()) {
Log.w(TAG, "Opened " + mName + " in read-only mode");
}

mDatabase = db;
return db;
} finally {
mIsInitializing = false;
if (db != null && db != mDatabase) {
db.close();
}
}
}

注意 oncreate()和 onUpgrade方法，

public abstract class SQLiteOpenHelper{
/*** Called when the database is created for the first time. This is where the creation of tables and the initial population of the tables should happen. @param db The database.
*/
public abstract void onCreate(SQLiteDatabase db);
}

/** @param db The database.
* @param oldVersion The old database version.
* @param newVersion The new database version.
*/
public abstract void onUpgrade(SQLiteDatabase db, int
oldVersion, int newVersion);

onCreate 和 onUpgrade是抽象方法

String filePath = MainActivity.this.getFilesDir().getAbsolutePath()+"/testMusic2.db";

SQLiteDatabase db = SQLiteDatabase.openOrCreateDatabase(filePath, null);