android:四大组件之一content provider

ContentProvider（内容提供者）是Android中的四大组件之一。主要用于对外共享数据，也就是通过ContentProvider把应用中的数据共享给其他应用访问，其他应用可以通过ContentProvider对指定应用中的数据进行操作，统一了数据访问的方式。可以类似的比作访问网页网页获取数据，或者SOA.

1、ContentProvider

主要方法：

public boolean onCreate() 在创建ContentProvider时调用

public Cursor query(Uri, String[], String, String[], String) 用于查询指定Uri的ContentProvider，返回一个Cursor

public Uri insert(Uri, ContentValues) 用于添加数据到指定Uri的ContentProvider中

public int update(Uri, ContentValues, String, String[]) 用于更新指定Uri的ContentProvider中的数据

public int delete(Uri, String, String[]) 用于从指定Uri的ContentProvider中删除数据

public String getType(Uri) 用于返回指定的Uri中的数据的MIME类型

getType
集合类型：vnd.android.cursor.dir/
非集合类型：vnd.android.cursor.item/

2、ContentResolver

当外部应用需要对ContentProvider中的数据进行添加、删除、修改和查询操作时，可以使用ContentResolver类来完成，要获取ContentResolver对象，可以使用Context提供的getContentResolver()方法。

ContentResolver提供的方法和ContentProvider提供的方法对应的有以下几个方法。

public Uri insert(Uri uri, ContentValues values) 用于添加数据到指定Uri的ContentProvider中。

public int delete(Uri uri, String selection, String[] selectionArgs) 用于从指定Uri的ContentProvider中删除数据。

public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) 用于更新指定Uri的ContentProvider中的数据。

public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) 用于查询指定Uri的ContentProvider。

下面是实现的代码：

UserInfoProvider .java

public class UserInfoProvider extends ContentProvider {
    private DBOpenHelp dbOpenHelper;
    private static final UriMatcher MATCHER = new UriMatcher(UriMatcher.NO_MATCH);
    private static final int USERS = 1;
    private static final int USER = 2;
    static{             
        MATCHER.addURI("com.example.sqlitetest.userprovider", "user_info", USERS);
        MATCHER.addURI("com.example.sqlitetest.userprovider", "user_info/#", USER);
    }
    @Override
    public boolean onCreate() {
        dbOpenHelper = new DBOpenHelp(this.getContext());
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
        switch (MATCHER.match(uri)) {
        case USERS:
            return db.query("user_info", projection, selection, selectionArgs, null, null, sortOrder);

        case USER:
            long rowid = ContentUris.parseId(uri);
            String where = "user_id="+ rowid;
            if(selection!=null && !"".equals(selection.trim())){
                where += " and "+ selection;
            }
            return db.query("user_info", projection, where, selectionArgs, null, null, sortOrder);
        default:
            throw new IllegalArgumentException("this is Unknown Uri:"+ uri);
        }
    }

    @Override
    public String getType(Uri uri) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        SQLiteDatabase db= dbOpenHelper.getWritableDatabase();
        switch (MATCHER.match(uri)) {
        case USERS:

            /**
             * long android.database.sqlite.SQLiteDatabase.insert
             * (String table, String nullColumnHack, ContentValues values)
             * 
             */

            long rowid = db.insert("user_info" , "user_name" , values);

            Uri insertUri = ContentUris.withAppendedId(uri, rowid);
            this.getContext().getContentResolver().notifyChange(uri, null);
            return insertUri;

        default:
            throw new IllegalArgumentException("this is Unknown Uri:"+ uri);
        }
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
        int num = 0;
        switch (MATCHER.match(uri)) {
        case USERS:
            num = db.delete("user_info", selection, selectionArgs);
            break;
        case USER:
            long rowid = ContentUris.parseId(uri);
            String where = "user_id="+ rowid;
            if(selection!=null && !"".equals(selection.trim())){
                where += " and "+ selection;
            }
            num = db.delete("user_info", where, selectionArgs);
            break;
        default:
            throw new IllegalArgumentException("this is Unknown Uri:"+ uri);
        }
        return num;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs) {
        SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
        int num = 0;
        switch (MATCHER.match(uri)) {
        case USERS:
            num = db.update("user_info", values, selection, selectionArgs);
            break;
        case USER:
            long rowid = ContentUris.parseId(uri);
            String where = "user_id="+ rowid;
            if(selection!=null && !"".equals(selection.trim())){
                where += " and "+ selection;
            }
            num = db.update("user_info", values, where, selectionArgs);
            break;
        default:
            throw new IllegalArgumentException("this is Unknown Uri:"+ uri);
        }
        return num;
    }
}

UserInfo .java

public class UserInfo {

    int       user_id;
    String  user_name;
    int      user_age;

    public UserInfo(int user_id, String user_name, int user_age) {
        super();
        this.user_id = user_id;
        this.user_name = user_name;
        this.user_age = user_age;
    }
    public int getUser_id() {
        return user_id;
    }
    public void setUser_id(int user_id) {
        this.user_id = user_id;
    }
    public String getUser_name() {
        return user_name;
    }
    public void setUser_name(String user_name) {
        this.user_name = user_name;
    }
    public int getUser_age() {
        return user_age;
    }
    public void setUser_age(int user_age) {
        this.user_age = user_age;
    }
    @Override
    public String toString() {
        return "UserInfo [user_id=" + user_id + ", user_name=" + user_name
                + ", user_age=" + user_age + "]";
    }
}

AndroidManifest.xml

提示：报错java.lang.SecurityException:Permission Denial

需要在provider中添加：android:exported=”true”

<provider
     android:name=".UserInfoProvider"
     android:authorities="com.example.sqlitetest.userprovider" 
     android:exported="true" />

新建一个TestAPP工程测试这个方法：

public class test extends AndroidTestCase{

    public void testInsert() throws Exception{                                     
        Uri uri = Uri.parse("content://com.example.sqlitetest.userprovider/user_info");
        ContentResolver resolver = this.getContext().getContentResolver();
        ContentValues values = new ContentValues();
        values.put("user_age", 18);
        values.put("user_name", "bank_atm");
        resolver.insert(uri, values);
    }  

    public void testDelete() throws Exception{
        Uri uri = Uri.parse("content://com.example.sqlitetest.userprovider/user_info");
        ContentResolver resolver = this.getContext().getContentResolver();
        resolver.delete(uri, null, null);
    }

    public void testUpdate() throws Exception{
        Uri uri = Uri.parse("content://com.example.sqlitetest.userprovider/user_info/41");
        ContentResolver resolver = this.getContext().getContentResolver();
        ContentValues values = new ContentValues();
        values.put("user_name", "xiaoniu");
        resolver.update(uri, values, null, null);
    }

    public void testQuery() throws Exception{
        Uri uri = Uri.parse("content://com.example.sqlitetest.userprovider/user_info");
        ContentResolver resolver = this.getContext().getContentResolver();
        Cursor cursor = resolver.query(uri, null, null, null, "user_id asc");
        if(cursor.getCount()>0){
        while(cursor.moveToNext()){
            String name = cursor.getString(cursor.getColumnIndex("user_name"));
            Log.i("TEST", name);
        }}
        cursor.close();
    }
}