今天，我跟着视频的教程完成了一次数据库的创建和增删改查，当我准备将核心代码写到项目中时，发现了一个决策性的问题，就是我们的空教室项目并不要求用户去实现增删改的功能，数据库应该是我们实现就存入的，学生只要能查询到空教室就可以，如果在数据库中逐条添加数据，未免也太麻烦了。因此，我在网上找到了相关的解决方法，就是用SQLITE可视化工具去编写一个db文件，在导入项目中，值得注意的问题是用可视化工具创建数据库文件时首先要存放在指定路径文件下，但是SQLITE提醒的是打开文件，这里是让用户去命名文件，并不是去打开已有的文件，网上关于这个问题并没有详细说明，其实是很简单的，可能是我自己钻牛角尖了，浪费了好多时间。创建数据库和表不难，和以前用过的比如SQLSERVER或者MYSQL差不多，创建好的db文件就在那你当时规定的路径文件下。
/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.database.sqlite;
import android.annotation.IntRange;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.content.Context;
import android.database.DatabaseErrorHandler;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.os.FileUtils;
import android.util.Log;
import com.android.internal.util.Preconditions;
import java.io.File;
/**
* A helper class to manage database creation and version management.
*
* <p>You create a subclass implementing {@link #onCreate}, {@link #onUpgrade} and
* optionally {@link #onOpen}, and this class takes care of opening the database
* if it exists, creating it if it does not, and upgrading it as necessary.
* Transactions are used to make sure the database is always in a sensible state.
*
* <p>This class makes it easy for {@link android.content.ContentProvider}
* implementations to defer opening and upgrading the database until first use,
* to avoid blocking application startup with long-running database upgrades.
*
* <p>For an example, see the NotePadProvider class in the NotePad sample application,
* in the <em>samples/</em> directory of the SDK.</p>
*
* <p class="note"><strong>Note:</strong> this class assumes
* monotonically increasing version numbers for upgrades.</p>
*/
public abstract class SQLiteOpenHelper {
private static final String TAG = SQLiteOpenHelper.class.getSimpleName();
private final Context mContext;
private final String mName;
private final int mNewVersion;
private final int mMinimumSupportedVersion;
private SQLiteDatabase mDatabase;
private boolean mIsInitializing;
private SQLiteDatabase.OpenParams.Builder mOpenParamsBuilder;
/**
* Create a helper object to create, open, and/or manage a database.
* This method always returns very quickly. The database is not actually
* created or opened until one of {@link #getWritableDatabase} or
* {@link #getReadableDatabase} is called.
*
* @param context to use for locating paths to the the database
* @param name of the database file, or null for an in-memory database
* @param factory to use for creating cursor objects, or null for the default
* @param version number of the database (starting at 1); if the database is older,
* {@link #onUpgrade} will be used to upgrade the database; if the database is
* newer, {@link #onDowngrade} will be used to downgrade the database
*/
public SQLiteOpenHelper(@Nullable Context context, @Nullable String name,
@Nullable CursorFactory factory, int version) {
this(context, name, factory, version, null);
}
/**
* Create a helper object to create, open, and/or manage a database.
* The database is not actually created or opened until one of
* {@link #getWritableDatabase} or {@link #getReadableDatabase} is called.
*
* <p>Accepts input param: a concrete instance of {@link DatabaseErrorHandler} to be
* used to handle corruption when sqlite reports database corruption.</p>
*
* @param context to use for locating paths to the the database
* @param name of the database file, or null for an in-memory database
* @param factory to use for creating cursor objects, or null for the default
* @param version number of the database (starting at 1); if the database is older,
* {@link #onUpgrade} will be used to upgrade the database; if the database is
* newer, {@link #onDowngrade} will be used to downgrade the database
* @param errorHandler the {@link DatabaseErrorHandler} to be used when sqlite reports database
* corruption, or null to use the default error handler.
*/
public SQLiteOpenHelper(@Nullable Context context, @Nullable String name,
@Nullable CursorFactory factory, int version,
@Nullable DatabaseErrorHandler errorHandler) {
this(context, name, factory, version, 0, errorHandler);
}
/**
* Create a helper object to create, open, and/or manage a database.
* This method always returns very quickly. The database is not actually
* created or opened until one of {@link #getWritableDatabase} or
* {@link #getReadableDatabase} is called.
*
* @param context to use for locating paths to the the database
* @param name of the database file, or null for an in-memory database
* @param version number of the database (starting at 1); if the database is older,
* {@link #onUpgrade} will be used to upgrade the database; if the database is
* newer, {@link #onDowngrade} will be used to downgrade the database
* @param openParams configuration parameters that are used for opening {@link SQLiteDatabase}.
* Please note that {@link SQLiteDatabase#CREATE_IF_NECESSARY} flag will always be
* set when the helper opens the database
*/
public SQLiteOpenHelper(@Nullable Context context, @Nullable String name, int version,
@NonNull SQLiteDatabase.OpenParams openParams) {
this(context, name, version, 0, openParams.toBuilder());
}
/**
* Same as {@link #SQLiteOpenHelper(Context, String, CursorFactory, int, DatabaseErrorHandler)}
* but also accepts an integer minimumSupportedVersion as a convenience for upgrading very old
* versions of this database that are no longer supported. If a database with older version that
* minimumSupportedVersion is found, it is simply deleted and a new database is created with the
* given name and version
*
* @param context to use for locating paths to the the database
* @param name the name of the database file, null for a temporary in-memory database
* @param factory to use for creating cursor objects, null for default
* @param version the required version of the database
* @param minimumSupportedVersion the minimum version that is supported to be upgraded to
* {@code version} via {@link #onUpgrade}. If the current database version is lower
* than this, database is simply deleted and recreated with the version passed in
* {@code version}. {@link #onBeforeDelete} is called before deleting the database
* when this happens. This is 0 by default.
* @param errorHandler the {@link DatabaseErrorHandler} to be used when sqlite reports database
* corruption, or null to use the default error handler.
* @see #onBeforeDelete(SQLiteDatabase)
* @see #SQLiteOpenHelper(Context, String, CursorFactory, int, DatabaseErrorHandler)
* @see #onUpgrade(SQLiteDatabase, int, int)
* @hide
*/
public SQLiteOpenHelper(@Nullable Context context, @Nullable String name,
@Nullable CursorFactory factory, int version,
int minimumSupportedVersion, @Nullable DatabaseErrorHandler errorHandler) {
this(context, name, version, minimumSupportedVersion,
new SQLiteDatabase.OpenParams.Builder());
mOpenParamsBuilder.setCursorFactory(factory);
mOpenParamsBuilder.setErrorHandler(errorHandler);
}
private SQLiteOpenHelper(@Nullable Context context, @Nullable String name, int version,
int minimumSupportedVersion,
@NonNull SQLiteDatabase.OpenParams.Builder openParamsBuilder) {
Preconditions.checkNotNull(openParamsBuilder);
if (version < 1) throw new IllegalArgumentException("Version must be >= 1, was " + version);
mContext = context;
mName = name;
mNewVersion = version;
mMinimumSupportedVersion = Math.max(0, minimumSupportedVersion);
setOpenParamsBuilder(openParamsBuilder);
}
/**
* Return the name of the SQLite database being opened, as given to
* the constructor.
*/
public String getDatabaseName() {
return mName;
}
/**
* Enables or disables the use of write-ahead logging for the database.
*
* Write-ahead logging cannot be used with read-only databases so the value of
* this flag is ignored if the database is opened read-only.
*
* @param enabled True if write-ahead logging should be enabled, false if it
* should be disabled.
*
* @see SQLiteDatabase#enableWriteAheadLogging()
*/
public void setWriteAheadLoggingEnabled(boolean enabled) {
synchronized (this) {
if (mOpenParamsBuilder.isWriteAheadLoggingEnabled() != enabled) {
if (mDatabase != null && mDatabase.isOpen() && !mDatabase.isReadOnly()) {
if (enabled) {
mDatabase.enableWriteAheadLogging();
} else {
mDatabase.disableWriteAheadLogging();
}
}
mOpenParamsBuilder.setWriteAheadLoggingEnabled(enabled);
}
// Compatibility WAL is disabled if an app disables or enables WAL
mOpenParamsBuilder.addOpenFlags(SQLiteDatabase.DISABLE_COMPATIBILITY_WAL);
}
}
/**
* Configures <a href="https://sqlite.org/malloc.html#lookaside">lookaside memory allocator</a>
*
* <p>This method should be called from the constructor of the subclass,
* before opening the database, since lookaside memory configuration can only be changed
* when no connection is using it
*
* <p>SQLite default settings will be used, if this method isn't called.
* Use {@code setLookasideConfig(0,0)} to disable lookaside
*
* <p><strong>Note:</strong> Provided slotSize/slotCount configuration is just a recommendation.
* The system may choose different values depending on a device, e.g. lookaside allocations
* can be disabled on low-RAM devices
*
* @param slotSize The size in bytes of each lookaside slot.
* @param slotCount The total number of lookaside memory slots per database connection.
*/
public void setLookasideConfig(@IntRange(from = 0) final int slotSize,
@IntRange(from = 0) final int slotCount) {
synchronized (this) {
if (mDatabase != null && mDatabase.isOpen()) {
throw new IllegalStateException(
"Lookaside memory config cannot be changed after opening the database");
}
mOpenParamsBuilder.setLookasideConfig(slotSize, slotCount);
}
}
/**
* Sets configuration parameters that are used for opening {@link SQLiteDatabase}.
* <p>Please note that {@link SQLiteDatabase#CREATE_IF_NECESSARY} flag will always be set when
* opening the database
*
* @param openParams configuration parameters that are used for opening {@link SQLiteDatabase}.
* @throws IllegalStateException if the database is already open
*/
public void setOpenParams(@NonNull SQLiteDatabase.OpenParams openParams) {
Preconditions.checkNotNull(openParams);
synchronized (this) {
if (mDatabase != null && mDatabase.isOpen()) {
throw new IllegalStateException(
"OpenParams cannot be set after opening the database");
}
setOpenParamsBuilder(new SQLiteDatabase.OpenParams.Builder(openParams));
}
}
private void setOpenParamsBuilder(SQLiteDatabase.OpenParams.Builder openParamsBuilder) {
mOpenParamsBuilder = openParamsBuilder;
mOpenParamsBuilder.addOpenFlags(SQLiteDatabase.CREATE_IF_NECESSARY);
}
/**
* Sets the maximum number of milliseconds that SQLite connection is allowed to be idle
* before it is closed and removed from the pool.
*
* <p>This method should be called from the constructor of the subclass,
* before opening the database
*
* @param idleConnectionTimeoutMs timeout in milliseconds. Use {@link Long#MAX_VALUE} value
* to allow unlimited idle connections.
*/
public void setIdleConnectionTimeout(@IntRange(from = 0) final long idleConnectionTimeoutMs) {
synchronized (this) {
if (mDatabase != null && mDatabase.isOpen()) {
throw new IllegalStateException(
"Connection timeout setting cannot be changed after opening the database");
}
mOpenParamsBuilder.setIdleConnectionTimeout(idleConnectionTimeoutMs);
}
}
/**
* Create and/or open a database that will be used for reading and writing.
* The first time this is called, the database will be opened and
* {@link #onCreate}, {@link #onUpgrade} and/or {@link #onOpen} will be
* called.
*
* <p>Once opened successfully, the database is cached, so you can
* call this method every time you need to write to the database.
* (Make sure to call {@link #close} when you no longer need the database.)
* Errors such as bad permissions or a full disk may cause this method
* to fail, but future attempts may succeed if the problem is fixed.</p>
*
* <p class="caution">Database upgrade may take a long time, you
* should not call this method from the application main thread, including
* from {@link android.content.ContentProvider#onCreate ContentProvider.onCreate()}.
*
* @throws SQLiteException if the database cannot be opened for writing
* @return a read/write database object valid until {@link #close} is called
*/
public SQLiteDatabase getWritableDatabase() {
synchronized (this) {
return getDatabaseLocked(true);
}
}
/**
* Create and/or open a database. This will be the same object returned by
* {@link #getWritableDatabase} unless some problem, such as a full disk,
* requires the database to be opened read-only. In that case, a read-only
* database object will be returned. If the problem is fixed, a future call
* to {@link #getWritableDatabase} may succeed, in which case the read-only
* database object will be closed and the read/write object will be returned
* in the future.
*
* <p class="caution">Like {@link #getWritableDatabase}, this method may
* take a long time to return, so you should not call it from the
* application main thread, including from
* {@link android.content.ContentProvider#onCreate ContentProvider.onCreate()}.
*
* @throws SQLiteException if the database cannot be opened
* @return a database object valid until {@link #getWritableDatabase}
* or {@link #close} is called.
*/
public SQLiteDatabase getReadableDatabase() {
synchronized (this) {
return getDatabaseLocked(false);
}
}
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.createInMemory(mOpenParamsBuilder.build());
} else {
final File filePath = mContext.getDatabasePath(mName);
SQLiteDatabase.OpenParams params = mOpenParamsBuilder.build();
try {
db = SQLiteDatabase.openDatabase(filePath, params);
// Keep pre-O-MR1 behavior by resetting file permissions to 660
setFilePermissionsForDb(filePath.getPath());
} catch (SQLException ex) {
if (writable) {
throw ex;
}
Log.e(TAG, "Couldn't open " + mName
+ " for writing (will try read-only):", ex);
params = params.toBuilder().addOpenFlags(SQLiteDatabase.OPEN_READONLY).build();
db = SQLiteDatabase.openDatabase(filePath, params);
}
}
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);
}
if (version > 0 && version < mMinimumSupportedVersion) {
File databaseFile = new File(db.getPath());
onBeforeDelete(db);
db.close();
if (SQLiteDatabase.deleteDatabase(databaseFile)) {
mIsInitializing = false;
return getDatabaseLocked(writable);
} else {
throw new IllegalStateException("Unable to delete obsolete database "
+ mName + " with version " + version);
}
} else {
db.beginTransaction();
try {
if (version == 0) {
onCreate(db);
} else {
if (version > mNewVersion) {
onDowngrade(db, version, mNewVersion);
} else {
onUpgrade(db, version, mNewVersion);
}
}
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();
}
}
}
private static void setFilePermissionsForDb(String dbPath) {
int perms = FileUtils.S_IRUSR | FileUtils.S_IWUSR | FileUtils.S_IRGRP | FileUtils.S_IWGRP;
FileUtils.setPermissions(dbPath, perms, -1, -1);
}
/**
* Close any open database object.
*/
public synchronized void close() {
if (mIsInitializing) throw new IllegalStateException("Closed during initialization");
if (mDatabase != null && mDatabase.isOpen()) {
mDatabase.close();
mDatabase = null;
}
}
/**
* Called when the database connection is being configured, to enable features such as
* write-ahead logging or foreign key support.
* <p>
* This method is called before {@link #onCreate}, {@link #onUpgrade}, {@link #onDowngrade}, or
* {@link #onOpen} are called. It should not modify the database except to configure the
* database connection as required.
* </p>
* <p>
* This method should only call methods that configure the parameters of the database
* connection, such as {@link SQLiteDatabase#enableWriteAheadLogging}
* {@link SQLiteDatabase#setForeignKeyConstraintsEnabled}, {@link SQLiteDatabase#setLocale},
* {@link SQLiteDatabase#setMaximumSize}, or executing PRAGMA statements.
* </p>
*
* @param db The database.
*/
public void onConfigure(SQLiteDatabase db) {}
/**
* Called before the database is deleted when the version returned by
* {@link SQLiteDatabase#getVersion()} is lower than the minimum supported version passed (if at
* all) while creating this helper. After the database is deleted, a fresh database with the
* given version is created. This will be followed by {@link #onConfigure(SQLiteDatabase)} and
* {@link #onCreate(SQLiteDatabase)} being called with a new SQLiteDatabase object
*
* @param db the database opened with this helper
* @see #SQLiteOpenHelper(Context, String, CursorFactory, int, int, DatabaseErrorHandler)
* @hide
*/
public void onBeforeDelete(SQLiteDatabase db) {
}
/**
* 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);
/**
* Called when the database needs to be upgraded. The implementation
* should use this method to drop tables, add tables, or do anything else it
* needs to upgrade to the new schema version.
*
* <p>
* The SQLite ALTER TABLE documentation can be found
* <a href="http://sqlite.org/lang_altertable.html">here</a>. If you add new columns
* you can use ALTER TABLE to insert them into a live table. If you rename or remove columns
* you can use ALTER TABLE to rename the old table, then create the new table and then
* populate the new table with the contents of the old table.
* </p><p>
* This method executes within a transaction. If an exception is thrown, all changes
* will automatically be rolled back.
* </p>
*
* @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);
/**
* Called when the database needs to be downgraded. This is strictly similar to
* {@link #onUpgrade} method, but is called whenever current version is newer than requested one.
* However, this method is not abstract, so it is not mandatory for a customer to
* implement it. If not overridden, default implementation will reject downgrade and
* throws SQLiteException
*
* <p>
* This method executes within a transaction. If an exception is thrown, all changes
* will automatically be rolled back.
* </p>
*
* @param db The database.
* @param oldVersion The old database version.
* @param newVersion The new database version.
*/
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
throw new SQLiteException("Can't downgrade database from version " +
oldVersion + " to " + newVersion);
}
/**
* Called when the database has been opened. The implementation
* should check {@link SQLiteDatabase#isReadOnly} before updating the
* database.
* <p>
* This method is called after the database connection has been configured
* and after the database schema has been created, upgraded or downgraded as necessary.
* If the database connection must be configured in some way before the schema
* is created, upgraded, or downgraded, do it in {@link #onConfigure} instead.
* </p>
*
* @param db The database.
*/
public void onOpen(SQLiteDatabase db) {}
}