如何创建一个ContentProvider，提供给其他App访问

一、概述
内容提供者是封装一套给其他APP访问此APP数据的接口，并提供安全的权限机制，如何数据不用提供给其他应用访问的话，使用数据库就可以了，内容提供者更加强调的是需要跨应用。

二、编码思路
1、使用SQliteOpenHelper类，创建一个数据库。
2、写一个类继承ContentPrivoder实现抽象方法
3、定义一套访问的此ContentPrivoder的唯一路径
4、用ContentResolver对象去访问ContentPrivoder进行增删改查

1、创建DBHelper类继承SqLiteOpenHelper类

package com.kuxiao.train.contentprovider.db;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;public class DBhelper extends SQLiteOpenHelper {    private static DBhelper mDBhelper = null;    private static final String DB_NAME = "myDB.db";//数据库名字    private static final int DB_VERSION = 1;//数据库版本号    //建表语句    public static final String CREATE_TABLE = "create table user_info(_id Integer primary key autoincrement,"            + "user_id Integer,user_name text,user_address text,user_password text,user_number Integer)";    //删表语句    public static final String DROP_TABLE = "drop table if exists user_info";    private DBhelper(Context context) {        super(context, DB_NAME, null, DB_VERSION);    }    //单例模式    public static DBhelper getInstance(Context context) {        if (mDBhelper == null) {            synchronized (new Object()) {                if (mDBhelper == null) {                    mDBhelper = new DBhelper(context);                }            }        }        return mDBhelper;    }    @Override    public void onCreate(SQLiteDatabase db) {           db.execSQL(CREATE_TABLE);    }    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {          db.execSQL(DROP_TABLE);          db.execSQL(CREATE_TABLE);    }}

2、创建一个类继承ContentProvider类，实现方法，并定义好访问匹配

package com.kuxiao.train.contentprovider.db;import android.content.ContentProvider;import android.content.ContentUris;import android.content.ContentValues;import android.content.UriMatcher;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.net.Uri;import android.util.Log;public class UserContentProvider extends ContentProvider {    private static final String TAG = "UserContentProvider";    private DBhelper mDBhelper = null;    // Uri匹配器    private static final UriMatcher MATCHER = new UriMatcher(            UriMatcher.NO_MATCH);    public static final int USER = 1;// 操作单条数据    public static final int USERS = 2;// 操作多条数据    static {        // 增加俩条匹配规则        MATCHER.addURI("com.kuxiao.train.contentprovider.UserContentProvider",                "user_info/#", USER);        MATCHER.addURI("com.kuxiao.train.contentprovider.UserContentProvider",                "user_info", USERS);    }    @Override    public boolean onCreate() {        mDBhelper = DBhelper.getInstance(getContext());        return true;    }    @Override    public Cursor query(Uri uri, String[] projection, String selection,            String[] selectionArgs, String sortOrder) {        //        Cursor cursor = null;        SQLiteDatabase db = mDBhelper.getReadableDatabase();        switch (MATCHER.match(uri)) {        case USER:            long id = ContentUris.parseId(uri);            String select = "_id = " + id;            if(selection != null && !selection.equals(""))            {                   select += "and" + selection;            }           cursor = db.query("user_info", projection, select, selectionArgs, null, null, sortOrder);            break;        case USERS:            cursor = db.query("user_info", projection, selection, selectionArgs, null, null, sortOrder);            break;        }        return cursor;    }    @Override    public String getType(Uri uri) {        switch (MATCHER.match(uri)) {        case USER:            return "vnd.android.cursor.item/com.kuxiao.train.contentprovider.UserContentProvider/user_info";        case USERS:            return "vnd.android.cursor.dir/com.kuxiao.train.contentprovider.UserContentProvider/user_info";        }        return null;    }    @Override    public Uri insert(Uri uri, ContentValues values) {        Uri  resultUri = null;        switch (MATCHER.match(uri)) {        case USER:            break;        case USERS:            SQLiteDatabase db = mDBhelper.getReadableDatabase();            long id = db.insert("user_info", null, values);//返回插入影响数据库的行数            resultUri = ContentUris.withAppendedId(uri, id);            break;        }        Log.i(TAG, resultUri.toString());        return resultUri;    }    @Override    public int delete(Uri uri, String selection, String[] selectionArgs) {        int con = -1;        int frag = MATCHER.match(uri);        SQLiteDatabase db = mDBhelper.getWritableDatabase();        switch (frag) {        case USER:            //解析客户端传过来的id            long id = ContentUris.parseId(uri);            String  vaule_name = "_id = " + id;             if(selection != null &&!selection.equals(""))              {                 //如果客户端传过来的选择语句不为空将进行累加                   vaule_name += "and" + selection;              }             con =  db.delete("user_info", vaule_name, selectionArgs);            break;        case USERS:              con = db.delete("user_info", selection, selectionArgs);            break;        }        db.close();        return con;    }    @Override    public int update(Uri uri, ContentValues values, String selection,            String[] selectionArgs) {         int con = -1;         // update user_info set name = ?,address = ? where id = ?;         SQLiteDatabase db = mDBhelper.getWritableDatabase();         switch (MATCHER.match(uri)) {        case USER:            long id = ContentUris.parseId(uri);             String value_name = "_id = " + id;             if(selection != null && !selection.equals(""))             {                   value_name += "and" + selection;             }            con =  db.update("user_info", values, value_name, selectionArgs);            break;        case USERS:            con = db.update("user_info", values, selection, selectionArgs);             break;        }        db.close();        Log.i(TAG, "----->>>影响的行数为 " +con);        return con;    }}

3、单元测试

package test;import android.content.ContentResolver;import android.content.ContentUris;import android.content.ContentValues;import android.database.Cursor;import android.net.Uri;import android.test.AndroidTestCase;import android.util.Log;public class Test extends AndroidTestCase {    public void insert() {        // 获取ContentResolver对象        ContentResolver contentResolver = getContext().getContentResolver();        // 构建解析路径：content://<authority>/<path>/<id> 单条        // content://<authority>/<path> 多条        Uri uri = Uri                .parse("content://com.kuxiao.train.contentprovider.UserContentProvider/user_info");        ContentValues values = new ContentValues();        values.put("user_id", 3);        values.put("user_name", "张万里");        values.put("user_address", "dalian");        values.put("user_password", "yw123456789");        values.put("user_number", 953751759);        contentResolver.insert(uri, values);    }    public void update() {        // 获取ContentResolver对象        ContentResolver resolver = getContext().getContentResolver();        // 构建Uri content:// + 授权 + 表名      Uri uri = Uri        .parse("content://com.kuxiao.train.contentprovider.UserContentProvider/user_info/6");        ContentValues values = new ContentValues();        values.put("user_id", 2);        values.put("user_name", "刘海洋");        values.put("user_address", "beijing");        values.put("user_password", "I love you liu haiyang");        values.put("user_number", 123456789);        resolver.update(uri, values, null, null);    }    public void delete() {        // 获取ContentResolver对象        ContentResolver resolver = getContext().getContentResolver();        // 构建Uri content:// + 授权 + 表名        Uri uri = Uri                .parse("content://com.kuxiao.train.contentprovider.UserContentProvider/user_info");        ContentValues values = new ContentValues();        resolver.delete(uri, null, null);    }    public void query() {        ContentResolver contentResolver = getContext().getContentResolver();        Uri uri = Uri                .parse("content://com.kuxiao.train.contentprovider.UserContentProvider/user_info");        Cursor cursor = contentResolver.query(uri, null, null, null, null);        while (cursor.moveToNext()) {            Log.i("UserContentProvider", "------->>>>>>"                    + cursor.getInt(cursor.getColumnIndex("user_id")));            Log.i("UserContentProvider", "------->>>>>>"                    + cursor.getString(cursor.getColumnIndex("user_name")));            Log.i("UserContentProvider", "------->>>>>>"                    + cursor.getString(cursor.getColumnIndex("user_address")));            Log.i("UserContentProvider", "------->>>>>>"                    + cursor.getString(cursor.getColumnIndex("user_password")));            Log.i("UserContentProvider", "------->>>>>>"                    + cursor.getInt(cursor.getColumnIndex("user_number")));        }    }}

四、主意事项
1、在清单文件增加授权

<provider android:name=".db.UserContentProvider"//授权一般是包名+类名            android:authorities="com.kuxiao.train.contentprovider.UserContentProvider"/>

2、定义访问路径标示符，操作单条与多条的区别

private static final UriMatcher MATCHER = new UriMatcher(            UriMatcher.NO_MATCH);    public static final int USER = 1;// 操作单条数据    public static final int USERS = 2;// 操作多条数据    static {        // 增加俩条匹配规则    //路径为：授权+数据库表名+标示符 （单条要在表名后加上/#号）    MATCHER.addURI("com.kuxiao.train.contentprovider.UserContentProvider",                "user_info/#", USER);        MATCHER.addURI("com.kuxiao.train.contentprovider.UserContentProvider",                "user_info", USERS);    }

3、重写getType方法是操作单条还是多条的区别

@Override    public String getType(Uri uri) {    //根据传过来的uri解析 返回对应的字符串，参考开发文档        switch (MATCHER.match(uri)) {        case USER:            return "vnd.android.cursor.item/com.kuxiao.train.contentprovider.UserContentProvider/user_info";        case USERS:            return "vnd.android.cursor.dir/com.kuxiao.train.contentprovider.UserContentProvider/user_info";        }        return null;    }

4、通过内容解析者访问时，路径定义

// 构建Uri content:// + 授权 + 表名 // 构建解析路径：content://<authority>/<path>/<id> 单条        // content://<authority>/<path> 多条        Uri uri = Uri                .parse("content://com.kuxiao.train.contentprovider.UserContentProvider/user_info/6");//单条                Uri uri = Uri                .parse("content://com.kuxiao.train.contentprovider.UserContentProvider/user_info"); //多条

五、特别说明：此都是小白成长记，有何不妥，欢迎指教。