Content Provider基础

1.Content Provider为存储和获取数据提供了统一的接口。

2.Content Provider可以在不同的应用程序之间共享数据。

3.Android为常见的一些数据提供了ContentProvider（包括音频，视频，图片和通讯录等）。

Manifest中加入：

<provider android:name="ycitss.cp.FirstContentProvider"
android:authorities="ycitss.cp.FirstContentProvider" />

DatabaseHelper.java:

package ycitss.sqlite3.db;

import ycitss.cp.FirstProviderMetaData;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase.CursorFactory;

//DatabaseHelper作为一个访问SQLite的助手类，提供两个方面的功能，

//第一，getReadableDatabase(),getWritableDatabase()可以获得SQLiteDatabse对象，通过该对象可以对数据库进行操作

//第二，提供了onCreate()和onUpgrade()两个回调函数，允许我们在创建和升级数据库时，进行自己的操作

 

public class DatabaseHelper extends SQLiteOpenHelper {

     

    private static final int VERSION = 1;

    //在SQLiteOepnHelper的子类当中，必须有该构造函数

    public DatabaseHelper(Context context, String name, CursorFactory factory,

            int version) {

        //必须通过super调用父类当中的构造函数

        super(context, name, factory, version);

        // TODO Auto-generated constructor stub

    }

    public DatabaseHelper(Context context,String name){

        this(context,name,VERSION);

    }

    public DatabaseHelper(Context context,String name,int version){

        this(context, name,null,version);

    }

 

    //该函数是在第一次创建数据库的时候执行,实际上是在第一次得到SQLiteDatabse对象的时候，才会调用这个方法

    @Override

    public void onCreate(SQLiteDatabase db) {

        // TODO Auto-generated method stub

        System.out.println("create a Database");

        //execSQL函数用于执行SQL语句

        db.execSQL("create table user(id int,name varchar(20))");

    }

 

    @Override

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

        // TODO Auto-generated method stub

        System.out.println("update a Database");

    }

 

}

　FirstProviderMetaData.java:

　

package ycitss.cp;

import android.net.Uri;
import android.provider.BaseColumns;

public class FirstProviderMetaData {
	public static final String AUTHORITY = "ycitss.cp.FirstContentProvider";
	//数据库名称
	public static final String DATABASE_NAME = "FirstProvider.db";
	//数据库的版本
	public static final int DATABASE_VERSION = 1;
	//表名
	public static final String USERS_TABLE_NAME = "users";

	public static final class UserTableMetaData implements BaseColumns {
		//表名
		public static final String TABLE_NAME = "users";
		//访问该ContenProvider的URI
		public static final Uri CONTENT_URI = Uri.parse("content://"
				+ AUTHORITY + "/users");
		//该ContentProvider所返回的数据类型的定义
		public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.firstprovider.user";
		public static final String CONTENT_TYPE_ITEM = "vnd.android.cursor.item/vnd.firstprovider.user";
		//列名
		public static final String USER_NAME = "name";
		//默认的排序方法
		public static final String DEFAULT_SORT_ORDER = "_id desc";
	}
}

FirstContentProvider.java

package ycitss.cp;

import java.util.HashMap;

import ycitss.cp.FirstProviderMetaData.UserTableMetaData;
import ycitss.sqlite3.db.DatabaseHelper;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;
import android.text.TextUtils;

public class FirstContentProvider extends ContentProvider {

	public static final UriMatcher uriMatcher;
	public static final int INCOMING_USER_COLLECTION = 1;
	public static final int INCOMING_USER_SINGLE = 2;

	private DatabaseHelper dh;

	static {
		uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
		uriMatcher.addURI(FirstProviderMetaData.AUTHORITY, "users",
				INCOMING_USER_COLLECTION);
		uriMatcher.addURI(FirstProviderMetaData.AUTHORITY, "users/#",
				INCOMING_USER_SINGLE);
	}

	public static HashMap<String, String> userProjectionMap;
	static {
		userProjectionMap = new HashMap<String, String>();
		userProjectionMap.put(UserTableMetaData._ID, UserTableMetaData._ID);
		userProjectionMap.put(UserTableMetaData.USER_NAME,
				UserTableMetaData.USER_NAME);
	}

	@Override
	public int delete(Uri arg0, String arg1, String[] arg2) {
		// TODO Auto-generated method stub
		System.out.println("delete...");
		return 0;
	}
	//根据传入的URI，返回该URI所表示的数据类型
	@Override
	public String getType(Uri uri) {
		System.out.println("getType...");
		switch (uriMatcher.match(uri)) {
		case INCOMING_USER_COLLECTION:
			return UserTableMetaData.CONTENT_TYPE;
		case INCOMING_USER_SINGLE:
			return UserTableMetaData.CONTENT_TYPE_ITEM;
		default:
			throw new IllegalArgumentException("Unknow URI " + uri);
		}
	}

	/**
	 * 该函数的返回值是一个Uri,这个Uri表示的是刚刚使用这个函数所传入的数据
	 * content://ycitss.cp.firstContentProivder/users/1
	 */
	@Override
	public Uri insert(Uri uri, ContentValues values) {
		System.out.println("insert...");
		SQLiteDatabase db = dh.getWritableDatabase();
		long rowId = db.insert(UserTableMetaData.TABLE_NAME, null, values);
		if (rowId > 0) {
			Uri insertedUserUri = ContentUris.withAppendedId(
					UserTableMetaData.CONTENT_URI, rowId);
			//通知监听器，数据已经改变
			getContext().getContentResolver().notifyChange(insertedUserUri,
					null);
			return insertedUserUri;
		}
		throw new SQLException("Failed to insert row into " + uri);
	}
	//是一个回调方法，所以说在ContentProvider创建的时候执行
	@Override
	public boolean onCreate() {
		//打开数据库
		dh = new DatabaseHelper(getContext(),
				FirstProviderMetaData.DATABASE_NAME);
		System.out.println("onCreate...");
		return true;
	}

	@Override
	public Cursor query(Uri uri, String[] projection, String selection,
			String[] selectionArgs, String sortOrder) {
		SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
		switch (uriMatcher.match(uri)) {
		case INCOMING_USER_COLLECTION:
			qb.setTables(UserTableMetaData.TABLE_NAME);
			qb.setProjectionMap(userProjectionMap);
			break;
		case INCOMING_USER_SINGLE:
			qb.setTables(UserTableMetaData.TABLE_NAME);
			qb.setProjectionMap(userProjectionMap);
			qb.appendWhere(UserTableMetaData._ID + "="
					+ uri.getPathSegments().get(1));
			break;
		}
		String orderBy;
		if (TextUtils.isEmpty(sortOrder)) {
			orderBy = UserTableMetaData.DEFAULT_SORT_ORDER;
		} else {
			orderBy = sortOrder;
		}
		SQLiteDatabase db = dh.getWritableDatabase();
		Cursor c = qb.query(db, projection, selection, selectionArgs, null,
				null, orderBy);
		c.setNotificationUri(getContext().getContentResolver(), uri);
		System.out.println("query...");
		return c;
	}

	@Override
	public int update(Uri uri, ContentValues values, String selection,
			String[] selectionArgs) {
		System.out.println("update...");
		return 0;
	}

}

CPActivity.java:

package ycitss.cp;

import ycitss.cp.FirstProviderMetaData.UserTableMetaData;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class CPActivity extends Activity {
	/** Called when the activity is first created. */
	private Button insertButton = null;
	private Button queryButton = null;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		insertButton = (Button) findViewById(R.id.insertButton);
		insertButton.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				ContentValues values = new ContentValues();
				values.put(FirstProviderMetaData.UserTableMetaData.USER_NAME,
						"zhangsan");
				Uri uri = getContentResolver().insert(
						FirstProviderMetaData.UserTableMetaData.CONTENT_URI,
						values);
				System.out.println("uri  ---> " + uri.toString());
			}
		});
		queryButton = (Button) findViewById(R.id.queryButton);
		queryButton.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				Cursor c = getContentResolver().query(
						FirstProviderMetaData.UserTableMetaData.CONTENT_URI,
						null, null, null, null);
				while (c.moveToNext()) {
					System.out.println(c.getString(c
							.getColumnIndex(UserTableMetaData.USER_NAME)));
				}

			}
		});
	}
}