/**
* Listing 8-14: A skeleton Content Provider implementation
*/
package com.paad.DatabaseSkeleton;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;
import android.text.TextUtils;
import android.util.Log;
public class MyContentProvider extends ContentProvider {
public static final Uri CONTENT_URI = Uri.parse("content://com.paad.skeletondatabaseprovider/elements");
/**
* Listing 8-8: Defining a UriMatcher to determine if a request is for all elements or a single row
*/
//Create the constants used to differentiate between the different URI
//requests. 创建两个常量来区分不同的URI请求
private static final int ALLROWS = 1;
private static final int SINGLE_ROW = 2;
private static final UriMatcher uriMatcher;
//Populate the UriMatcher object, where a URI ending in 填充UriMatcher对象，其中以elements结尾请求所有数据
//'elements' will correspond to a request for all items,
//and 'elements/[rowID]' represents a single row. 以elements/[rowID]结尾的请求单行数据
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI("com.paad.skeletondatabaseprovider",
"elements", ALLROWS);
uriMatcher.addURI("com.paad.skeletondatabaseprovider",
"elements/#", SINGLE_ROW);
}
/** */
// The index (key) column name for use in where clauses.
public static final String KEY_ID = "_id";
// The name and column index of each column in your database.
// These should be descriptive.
public static final String KEY_COLUMN_1_NAME = "KEY_COLUMN_1_NAME";
// TODO: Create public field for each column in your table.
/**
* Listing 8-9: Creating the Content Provider�s database
*/
private MySQLiteOpenHelper myOpenHelper;
@Override
public boolean onCreate() {
// Construct the underlying database. 构造底层数据库
// Defer opening the database until you need to perform 延迟打开数据库，直到需要执行
// a query or transaction. 一个查询或者事务时再打开
myOpenHelper = new MySQLiteOpenHelper(getContext(),
MySQLiteOpenHelper.DATABASE_NAME, null,
MySQLiteOpenHelper.DATABASE_VERSION);
return true;
}
/**
* Listing 8-10: Implementing queries and transactions within a Content Provider
*/
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
// Open thedatabase. 打开数据库
SQLiteDatabase db;
try {
db = myOpenHelper.getWritableDatabase();
} catch (SQLiteException ex) {
db = myOpenHelper.getReadableDatabase();
}
// Replace these with valid SQL statements if necessary. 必要的话使用有效的SQL语句替换这些语句
String groupBy = null;
String having = null;
// Use an SQLite Query Builder to simplify constructing the
// database query.用Query Builder 来简化构造数据库查询的过程
SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
// If this is a row query, limit the result set to the passed in row.
switch (uriMatcher.match(uri)) {
case SINGLE_ROW :
String rowID = uri.getPathSegments().get(1);
queryBuilder.appendWhere(KEY_ID + "=" + rowID);
default: break;
}
// Specify the table on which to perform the query. This can
// be a specific table or a join as required. 制定要执行查询的表
queryBuilder.setTables(MySQLiteOpenHelper.DATABASE_TABLE);
// Execute the query. 执行查询
Cursor cursor = queryBuilder.query(db, projection, selection,
selectionArgs, groupBy, having, sortOrder);
// Return the result Cursor. 返回结果Cursor
return cursor;
}
/**
* Listing 8-11: Returning a Content Provider MIME type 返回一个MIME类型来标识返回的数据
*/
@Override
public String getType(Uri uri) {
// Return a string that identifies the MIME type
// for a Content Provider URI
switch (uriMatcher.match(uri)) {
case ALLROWS:
return "vnd.android.cursor.dir/vnd.paad.elemental";
case SINGLE_ROW:
return "vnd.android.cursor.item/vnd.paad.elemental";
default:
throw new IllegalArgumentException("Unsupported URI: " +
uri);
}
}
/**
* Listing 8-12: Typical Content Provider transaction implementations
*/
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
// Open a read / write database to support the transaction. 打开一个可读可写的数据库来支持事务
SQLiteDatabase db = myOpenHelper.getWritableDatabase();
// If this is a row URI, limit the deletion to the specified row. 限定删除的行为为指定的行
switch (uriMatcher.match(uri)) {
case SINGLE_ROW :
String rowID = uri.getPathSegments().get(1);
selection = KEY_ID + "=" + rowID
+ (!TextUtils.isEmpty(selection) ?
" AND (" + selection + ')' : "");
default: break;
}
// To return the number of deleted items you must specify a where
// clause. To delete all rows and return a value pass in "1". 要想返回删除的项的数量，必须制定一条where字句。要删除所有行并返回一个值，则传入1
if (selection == null)
selection = "1";
// Perform the deletion. 执行删除
int deleteCount = db.delete(MySQLiteOpenHelper.DATABASE_TABLE,
selection, selectionArgs);
// Notify any observers of the change in the data set. 通知所有观察者，数据集已经改变
getContext().getContentResolver().notifyChange(uri, null);
// Return the number of deleted items. 返回删除的项的数量
return deleteCount;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
// Open a read / write database to support the transaction. 打开一个可读可写的数据库来支持事务
SQLiteDatabase db = myOpenHelper.getWritableDatabase();
// To add empty rows to your database by passing in an empty
// Content Values object you must use the null column hack
// parameter to specify the name of the column that can be
// set to null. 要想通过传入一个空content value对象来向数据库添加一个空行，必须使用nullColumnHack参数来制定可以设置为null的列名
String nullColumnHack = null;
// Insert the values into the table 向表中插入数据
long id = db.insert(MySQLiteOpenHelper.DATABASE_TABLE,
nullColumnHack, values);
// Construct and return the URI of the newly inserted row. 构造并返回新插入的行的URI
if (id > -1) {
// Construct and return the URI of the newly inserted row.
Uri insertedId = ContentUris.withAppendedId(CONTENT_URI, id);
// Notify any observers of the change in the data set.
getContext().getContentResolver().notifyChange(insertedId, null);
return insertedId;
}
else
return null;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
// Open a read / write database to support the transaction.
SQLiteDatabase db = myOpenHelper.getWritableDatabase();
// If this is a row URI, limit the deletion to the specified row.
switch (uriMatcher.match(uri)) {
case SINGLE_ROW :
String rowID = uri.getPathSegments().get(1);
selection = KEY_ID + "=" + rowID
+ (!TextUtils.isEmpty(selection) ?
" AND (" + selection + ')' : "");
default: break;
}
// Perform the update.
int updateCount = db.update(MySQLiteOpenHelper.DATABASE_TABLE,
values, selection, selectionArgs);
// Notify any observers of the change in the data set.
getContext().getContentResolver().notifyChange(uri, null);
return updateCount;
}
private static class MySQLiteOpenHelper extends SQLiteOpenHelper {
// Database name, version, and table names.
private static final String DATABASE_NAME = "myDatabase.db";
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_TABLE = "mainTable";
// SQL Statement to create a new database.
private static final String DATABASE_CREATE = "create table " +
DATABASE_TABLE + " (" + KEY_ID +
" integer primary key autoincrement, " +
KEY_COLUMN_1_NAME + " text not null);";
public MySQLiteOpenHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
}
// Called when no database exists in disk and the helper class needs
// to create a new one.
@Override
public void onCreate(SQLiteDatabase _db) {
_db.execSQL(DATABASE_CREATE);
}
// Called when there is a database version mismatch meaning that the version
// of the database on disk needs to be upgraded to the current version.
@Override
public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion) {
// Log the version upgrade.
Log.w("TaskDBAdapter", "Upgrading from version " +
_oldVersion + " to " +
_newVersion + ", which will destroy all old data");
// Upgrade the existing database to conform to the new version. Multiple
// previous versions can be handled by comparing _oldVersion and _newVersion
// values.
// The simplest case is to drop the old table and create a new one.
_db.execSQL("DROP TABLE IF IT EXISTS " + DATABASE_TABLE);
// Create a new one.
onCreate(_db);
}
}
}
