内容提供者学习

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11.ContentProvider 内容提供者

1.1. 什么是内容提供者

　　内容提供者是Android中的四大组件之一，可以将应用中的数据对外进行共享

　　内容提供者将数据的访问方式统一，不必针对不同数据类型采取不同的访问策略

　　内容提供者将数据封装，只暴露出我们希望提供给其他程序的数据

　　内容提供者中数据更改可被监听

1.2. 创建内容提供者

　　　定义类继承ContentProvider，根据需要重写内部方法

　　在清单文件的<application>节点下进行配置，<provider>标签中需要指定name和authorities属性

　　　　name为类名，包名从程序Package开始，以“.”开始

　　　　authorities：是访问Provider时的路径，要唯一

　　 URI代表要操作的数据，由scheme、authorites、path三部分组成

　　　　content://cn.itcast.provider.itcast/person

　　　　scheme：固定为content，代表访问内容提供者

　　　　authorites：<provider>节点中的authorites属性

　　　　path：程序定义的路径，可根据业务逻辑定义

1.3. 完成CRUD方法

Ÿ 当程序调用CRUD方法时会传入Uri

Ÿ 我们通过Uri判断调用者要操作的数据

可以使用工具类UriMatcher来判断Uri

addURI方法可以添加Uri

match方法可以匹配一个Uri判断其类型

Ÿ 根据业务逻辑操作数据

1.4. 完成getType方法

Ÿ 如果返回数据是单条数据：vnd.android.cursor.item

Ÿ 如果返回数据是多条数据：vnd.android.cursor.dir

public class PersonProvider extends android.content.ContentProvider {    private static final int PERSON = 0;    private static final int PERSON_ID = 1;    private UriMatcher matcher;    private DBOpenHelper helper;    @Override    public boolean onCreate() {        matcher = new UriMatcher(UriMatcher.NO_MATCH);        matcher.addURI("com.demo.sqlite.provider", "person", PERSON); // 添加一个可以匹配的Uri        matcher.addURI("com.demo.sqlite.provider", "person/#", PERSON_ID);        helper = new DBOpenHelper(getContext());        return true;    }    @Override    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {        switch (matcher.match(uri)) { // 对Uri进行匹配        case PERSON_ID:            String idSelection = "id = " + ContentUris.parseId(uri);    //  Converts the last path segment to a long.            // 注意此处字符串拼装            selection = selection == null ? idSelection : idSelection + " AND " + selection;        case PERSON:            SQLiteDatabase db = helper.getReadableDatabase();            return db.query("person", projection, selection, selectionArgs, null, null, sortOrder);        default:            throw new IllegalArgumentException("No Match Uri " + uri);        }    }    @Override    public Uri insert(Uri uri, ContentValues values) {        switch (matcher.match(uri)) {        case PERSON:            SQLiteDatabase db = helper.getWritableDatabase();            long id = db.insert("person", null, values);        // 使用 db.insert() 方法插入数据,返回 id                                                                                    // 而 db.exceSQL(sql)方式插入数据，返回 void            // return     Uri.parse("content://com.demo.sqlite.provider/person/" + id);        // 与下句效果相同            return ContentUris.withAppendedId(uri, id);        // Appends the given ID to the end of the path.            default:                throw new IllegalArgumentException("No Match Uri " + uri);        }    }    @Override    public int delete(Uri uri, String selection, String[] selectionArgs) {        switch (matcher.match(uri)) {        case PERSON_ID:            long id = ContentUris.parseId(uri);            selection = selection == null ? "id = " + id : "id = " +id + " AND " +selection;        case PERSON:            SQLiteDatabase db = helper.getWritableDatabase();            // return : The number of rows affected            return db.delete("person", selection, selectionArgs);         default:            throw new IllegalArgumentException("No Match Uri " + uri);        }    }    @Override    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {        switch (matcher.match(uri)) {        case PERSON_ID:            long id = ContentUris.parseId(uri);            selection = selection == null ? "id = " + id : "id = " + id + " AND " + selection;        case PERSON:            SQLiteDatabase db = helper.getWritableDatabase();            // @return the number of rows affected            return db.update("person", values, selection, selectionArgs);        default:            throw new IllegalArgumentException("No Match Uri " + uri);        }    }        @Override    public String getType(Uri uri) {        switch (matcher.match(uri)) {        case PERSON_ID:            return "vnd.android.cursor.item/person";        case PERSON:            return "vnd.android.cursor.dir/person";         default:            throw new IllegalArgumentException("No Match Uri " + uri);        }    }

1.5. 访问内容提供者

Ÿ 通过Context获得ContentResolver对象

Ÿ 调用ContentResolver对象的方法即可访问内容提供者

    private static final String TAG = "ProviderTest";    // 查询 id = 36    public void testQuery1() {        // 通过 ContentResolver 调用 ContentProvider 提供的方法        ContentResolver resolver = getContext().getContentResolver();        Uri uri = Uri.parse("content://com.demo.sqlite.provider/person");        Cursor c = resolver.query(uri, new String[] { "id", "name", "balance" }, "id = ?", new String[] { "36" }, null);        if (c.moveToNext()) {            Person person = new Person(c.getInt(0), c.getString(1), c.getInt(2));            Logger.i(TAG, person.toString());        }    }    // 查询所有 person    public void testQuery2() {        // 通过 ContentResolver 调用 ContentProvider 提供的方法        ContentResolver resolver = getContext().getContentResolver();        Uri uri = Uri.parse("content://com.demo.sqlite.provider/person");        Cursor c = resolver.query(uri, null, null, null, null);        while (c.moveToNext()) {            Person person = new Person(c.getInt(0), c.getString(1), c.getInt(2));            Logger.i(TAG, person.toString());        }    }    // 通过附带 id 查询 person    public void testQuery3() {        // 通过 ContentResolver 调用 ContentProvider 提供的方法        ContentResolver resolver = getContext().getContentResolver();        // Uri        Uri uri = Uri.parse("content://com.demo.sqlite.provider/person/55");        Cursor c = resolver.query(uri, null, "name = ?", new String[] { "Ashia_54" }, null);        while (c.moveToNext()) {            Person person = new Person(c.getInt(0), c.getString(1), c.getInt(2));            Logger.i(TAG, person.toString());        }    }    public void testInsert() {        ContentResolver resolver = getContext().getContentResolver();        Uri uri = Uri.parse("content://com.demo.sqlite.provider/person");        ContentValues values = new ContentValues();        Person person = new Person("another Person uri insert", 7000);        values.put("name", person.getName());        values.put("balance", person.getBalance());        Uri reUri = resolver.insert(uri, values);        Cursor c = resolver.query(reUri, null, null, null, null);        if (c.moveToNext()) {            Person rePerson = new Person(c.getInt(0), c.getString(1), c.getInt(2));            Logger.i(TAG, rePerson.toString());        }    }        public void testDelete() {        // ContentResolver :This class provides applications access to the content model.        ContentResolver resolver = getContext().getContentResolver();                Uri url = Uri.parse("content://com.demo.sqlite.provider/person/121");        // 忘记加 = ?, 异常如下        // android.database.sqlite.SQLiteException: bind or column index out of range         long id = resolver.delete(url, "name = ?", new String[] {"zhangsan"});         Logger.i(TAG, id + "");                  id = resolver.delete(url, null, null);         Logger.i(TAG, id + "");    }        public void testDeleteAll() {        ContentResolver resolver = getContext().getContentResolver();        Uri url = Uri.parse("content://com.demo.sqlite.provider/person");        int deleteNum = resolver.delete(url, null, null);        Logger.i(TAG, deleteNum + "");    }        public void testUpdate() {        ContentResolver resolver = getContext().getContentResolver();        Uri uri = Uri.parse("content://com.demo.sqlite.provider/person/122");        ContentValues values = new ContentValues();        values.put("balance", 8000);        int update = resolver.update(uri, values, "balance = ?", new String[] {"9000"});        Logger.i(TAG, update + "");    }        public void testUpdateById() {        ContentResolver resolver = getContext().getContentResolver();        ContentValues values = new ContentValues();        values.put("name", "new name");        values.put("balance", 7000);        values.put("id", 2);        Uri uri = Uri.parse("content://com.demo.sqlite.provider/person/123");        int update = resolver.update(uri, values, null, null);        Logger.i(TAG, update + "");    }    // Uri写错，异常    // java.lang.IllegalArgumentException: Unknown URI         // 主键 id 重复，异常    // android.database.sqlite.SQLiteConstraintException        public void testGetType() {        ContentResolver resolver = getContext().getContentResolver();        Uri uri = Uri.parse("content://com.demo.sqlite.provider/person/1");        Logger.i(TAG, resolver.getType(uri));        uri = Uri.parse("content://com.demo.sqlite.provider/person");        Logger.i(TAG, resolver.getType(uri));    }