背景
这几天在学习安卓进程间通信,而做为安卓四大组件之一的ContentProvider(内容提供者),也可以实现IPC。
现在记录一下使用步骤
步骤
1、创建DatabaseOpenHelper
内容提供者的工作方式就和数据库操作是一样的,增删改查,所以我们要先创建一个帮助类来创建数据库,代码如下
public class MyDbHelper extends SQLiteOpenHelper { public static final String DB_NAME = "peopleDatabase.db"; public static final String TABLE_NAME = "person"; public static final int VERSION = 1; public MyDbHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) { this(context); } public MyDbHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version, DatabaseErrorHandler errorHandler) { this(context); } public MyDbHelper(Context context) { super(context, DB_NAME, null, VERSION, null); } @Override public void onCreate(SQLiteDatabase db) { String sql = "create table if not exists " + TABLE_NAME + "(id int(3) not null, name varchar(20), description varchar(50), " + "constraint PK_PERSON primary key(id))"; db.execSQL(sql); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { } }
2、创建自己的内容提供者
代码如下
public class PersonProvider extends ContentProvider { private static final String TAG = "PersonProvider"; private static final UriMatcher MATCHER = new UriMatcher(UriMatcher.NO_MATCH); // uri匹配者 public static final String AUTH = "com.example.songzeceng.PersonProvider"; // 内容提供者的id public static final Uri PERSON_URI = Uri.parse("content://" + AUTH + "/person"); public static final String TYPE_MORE = "vnd.android.cursor.dir/person"; // 多条查询的type public static final String TYPE_SINGAL = "vnd.android.cursor.item/person"; // 单条查询的type public static final int CODE_SINGAL = 0; // 单条查询的匹配码 public static final int CODE_MORE = 1; // 多条查询的匹配码 public static String TABLE_NAME = "person"; private SQLiteDatabase mDatabase; private Context mContext; static { MATCHER.addURI(AUTH, "person", CODE_MORE); // 多条查询 MATCHER.addURI(AUTH, "person/#", CODE_SINGAL); // 单条查询,#是数字通配符,理解为id } @Override public boolean onCreate() { mContext = getContext(); mDatabase = new MyDbHelper(mContext).getWritableDatabase(); // 获取可写数据库,可写自然可读 return false; } @Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { // 参数列表:表的uri、要查询的列、where子句、where子句的参数、排序语句 System.out.println("query uri:"+uri.toString()); String type = getType(uri); if (isTypeValid(type)) { Cursor cursor = mDatabase.query(TABLE_NAME, projection, selection, selectionArgs, null, sortOrder, null); // 两个null分别是groupBy和orderBy return cursor; // 返回的是游标 } return null; } private boolean isTypeValid(String type) { return type != null && (TYPE_MORE.equals(type) || TYPE_SINGAL.equals(type)); } @Override public String getType(Uri uri) { int code = MATCHER.match(uri); switch (code) { case CODE_SINGAL: return TYPE_SINGAL; case CODE_MORE: return TYPE_MORE; } return null; } @Override public Uri insert(Uri uri, ContentValues values) { System.out.println("insert uri:"+uri.toString() + "--contentValues:"+values.toString()); if (isTypeValid(getType(uri))) { mDatabase.insert(TABLE_NAME, null, values); // null是nullColumnHack,用于插入空行(也就是ContentValues内容是空) mContext.getContentResolver().notifyChange(uri, null); // null是observer,观察者 } return null; } @Override public int delete(Uri uri, String selection, String[] selectionArgs) { // 参数列表:uri、where子句、where参数 System.out.println("delete uri:"+uri.toString()); if (isTypeValid(getType(uri))) { int count = mDatabase.delete(TABLE_NAME, selection, selectionArgs); if (count > 0) { mContext.getContentResolver().notifyChange(uri ,null); } } return 0; } @Override public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { System.out.println("update uri:"+uri.toString() + "--contentValues:"+values.toString()); if (isTypeValid(getType(uri))) { int count = mDatabase.update(TABLE_NAME, values, selection, selectionArgs); if (count > 0) { mContext.getContentResolver().notifyChange(uri, null); } } return 0; } }
可以看到,增加和更改的内容是放在ContentValues里面,这个相当于一个哈希映射
selection是where子句,selectionArgs则是参数,如果selection是"where id = ? and name = ? ",selectionArgs是[1,"szc"]的话,生成的完整的where子句就是"where id = 1 and name = \"szc\""
不过我直接把参数拼接到selection里了,所以selectionArgs就成了摆设
另外增加方法的返回值是表的url,修改和删除的返回值是影响的行数,感觉没啥大用..
3、清单文件中注册
<provider android:name=".PersonProvider" <!--provider类名--> android:authorities="com.example.songzeceng.PersonProvider" <!--provider的id--> android:exported="true" <!--是否允许别的进程访问--> android:grantUriPermissions="true" <!--是否允许解析uri--> android:process=":provider"> <!--provider所属进程名--> </provider>
4、在客户端进行CRUD检验
代码如下
public class MainActivity extends Activity { public static final String TAG = "MainActivity"; private void insertData(Uri providerUrl, int id, String name, String description) { ContentValues values = new ContentValues(); values.put("id", id); // 键值对 values.put("name", name); values.put("description", description); getContentResolver().insert(providerUrl, values); // 必须根据ContentResolver访问内容提供者 } private void updateData(Uri providerUrl, int id, String name, String description) { ContentValues values = new ContentValues(); values.put("id", id); values.put("name", name); values.put("description", description); getContentResolver().update(providerUrl, values, "id = " + id, null); // 第二个参数是where子句 ,null是where子句参数 } private void deleteData(Uri providerUrl, int id) { getContentResolver().delete(providerUrl, "id = " + id, null); // 第二个参数是where子句,null则是其参数 } private void queryData(Uri providerUrl) { Cursor cursor = getContentResolver().query(providerUrl, null, null, null, null); // 查询所有记录 while (cursor.moveToNext()) { // 只要游标没到底 int id = cursor.getInt(cursor.getColumnIndex("id")); // getColumnIndex()根据列名获取列的位置,而后getInt()根据列的位置获取列的值 String userName = cursor.getString(cursor.getColumnIndex("name")); String description = cursor.getString(cursor.getColumnIndex("description")); System.out.println(id + "--" + userName + "--" + description); } cursor.close(); // 莫忘记关游标 System.out.println("----------------------------------"); } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); try { Uri providerUrl = PersonProvider.PERSON_URI; insertData(providerUrl, 1, "szc", "a simple boy"); insertData(providerUrl, 2, "jason", "an interesting boy"); queryData(providerUrl); updateData(providerUrl, 2, "dustin", "a brave boy"); queryData(providerUrl); deleteData(providerUrl, 2); queryData(providerUrl); } catch (Exception e) { e.printStackTrace(); } }
5、查看结果
客户端截图
服务(provider)端截图
进程号不同,说明实现了进程间通信
结语
受限于水平和精力,没有怎么钻研内容提供者的源码,大致看了看源码和这篇文章,发现客户端contentResolver的insert()方法最终调用了IContentProvider的insert()方法,而IContentProvider接口继承了IInterface,似乎也是AIDL在幕后操纵,具体我就没去看了