Android的ContentProvider小记

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Android应用程序组件ContentProvider担任共享应用程序间数据的任务，它无须手动实例化，客户端可通过ContentResolver对象实现对ContentProvider的增、删、查、改的操作。

ContentResolver contentResolver = getContentResolver();

ContentProvider使用基于数据库模型的简单表格来提供其中的数据，访问ContentProvider的数据集则需要用到URI，URI的统一格式为：

content:// com.season.myprovider / tab / 1标准前缀      authority部分       路径部分 ID值

Android系统为常用数据类型提供了很多预定义的ContentProvider（声音，视频，图片，联系人等）,大多位于android.provider 包中，下面是书上一个读取联系人信息的小demo。

布局文件就一个RelativeLayout里放一个TextView

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context=".ContactActivity">    <TextView        android:id="@+id/tv"        android:layout_width="match_parent"        android:layout_height="match_parent"        ></TextView></RelativeLayout>

java代码如下：

public class ContactActivity extends AppCompatActivity {    //联系人表中的一些字段名    private String[] columns = {ContactsContract.Contacts._ID,            ContactsContract.Contacts.DISPLAY_NAME,            ContactsContract.CommonDataKinds.Phone.NUMBER,            ContactsContract.CommonDataKinds.Phone.CONTACT_ID};    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_contract);        TextView tv = (TextView) findViewById(R.id.tv);        tv.setText(getQueryData());    }    //获取查询到的信息    private String getQueryData() {        StringBuilder builder = new StringBuilder();        ContentResolver resolver = getContentResolver();        //查询联系人        Cursor cursor = resolver.query(ContactsContract.Contacts.CONTENT_URI, null,                null, null, null);        while (cursor.moveToNext()) {            int idIndex = cursor.getColumnIndex(columns[0]);            int nameIndex = cursor.getColumnIndex(columns[1]);            int id = cursor.getInt(idIndex);            String name = cursor.getString(nameIndex);            Cursor phone = resolver.query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,                    null, columns[3] + "=" + id, null, null);            while (phone.moveToNext()) {                String number = phone.getString(phone.getColumnIndex(columns[2]));                builder.append(name + ": " + number + "\n");            }        }        cursor.close();        return builder.toString();    }}

最后记得加权限：

<uses-permission android:name="android.permission.READ_CONTACTS" />

关于自定义ContentProvider

步骤：

建立数据库存储系统。到多数ContentProvider使用Android文件存储方法或者SQLite数据库保存数据，但是开发人员可以使用任何方式存储。Android提供了SQLiteOpenHelper类帮助创建数据库，SQLiteDatabase类帮助管理数据库
继承 ContentProvider类提供数据访问方式
在应用程序的AndroidManifest文件中声明ContentProvider。

下面是一个小demo：

MyContentProvider 类

public class MyContentProvider extends ContentProvider {    SQLiteDatabase database;    public static final Uri URI = Uri.parse("content://com.season.learncontentprovider");    private DBHelper dbHelper = null;    private String DB_name = "tab";    @Override    public boolean onCreate() {        dbHelper = new DBHelper(getContext(), DB_name, null, 1);        database = dbHelper.getWritableDatabase();        return false;    }    @Override    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {        Cursor cursor = database.query(DB_name, null, null, null, null, null, null);        return cursor;    }    @Override    public String getType(Uri uri) {        return null;    }    @Override    public Uri insert(Uri uri, ContentValues values) {        long id = database.insert(DB_name, "_id", values);    //Uri.withAppendedPath能轻松将ID加到URI        Uri newUri = Uri.withAppendedPath(uri, id + "");        getContext().getContentResolver().notifyChange(uri, null);        return newUri;    }    @Override    public int delete(Uri uri, String selection, String[] selectionArgs) {        getContext().getContentResolver().notifyChange(uri, null);        return database.delete(DB_name, selection, selectionArgs);    }    @Override    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {        return 0;    }//利用SQLiteOpenHelper来创建数据库表    private class DBHelper extends SQLiteOpenHelper {        public DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {            super(context, name, factory, version);        }        @Override        public void onCreate(SQLiteDatabase db) {            db.execSQL("create table tab(" +                    "_id integer primary key autoincrement," +                    "name text not null," +                    "sex text not null)");        }        @Override        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {            db.execSQL("drop table if exists " + DB_name);            onCreate(db);        }    }}

AndroidManifest文件中声明ContentProvider

<provider            android:name=".MyContentProvider"            android:exported="true"         android:authorities="com.season.learncontentprovider"/>

MainActivity类

public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        findViewById(R.id.btnWrite).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                write();                Toast.makeText(MainActivity.this, "写入成功", Toast.LENGTH_SHORT).show();            }        });    }    public void write() {        ContentValues cv = new ContentValues();        cv.put("name", "season");        cv.put("sex", "boy");        getContentResolver().insert(MyContentProvider.URI, cv);    }}

布局文件如下

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    >    <TextView        android:id="@+id/textView"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="season  boy"        android:textSize="25dp" />    <Button        android:id="@+id/btnWrite"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:layout_alignParentLeft="true"        android:layout_alignParentStart="true"        android:layout_below="@+id/textView"        android:layout_marginTop="37dp"        android:text="写入数据" /></RelativeLayout>

结果如下：
结果图

到这里就已经完成了一个应用程序的自定义contentprovider共享数据的准备工作了，下面将再新建一个项目来读取该项目的共享数据集了
布局文件就一个LinearLayout里放一个ListView：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    >    <ListView        android:id="@+id/list"        android:layout_width="match_parent"        android:layout_height="match_parent"></ListView></LinearLayout>

MainActivity 类

public class MainActivity extends AppCompatActivity {    ListView listView;    private static final Uri uri = Uri.parse("content://com.season.learncontentprovider");    //列名数组    private String[] column = new String[]{"_id", "name", "sex"};    //继承CursorAdapter的一个自定义adapter    private ExampleAdapter adapter; //继承了ContentObserver的自定义观察者类，用于监控provider数据改变    private InfoObserver observer;    private ContentResolver contentResolver;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        listView = (ListView) findViewById(R.id.list);        contentResolver = getContentResolver();        Cursor cursor = contentResolver.query(uri, null, null, null, null);        observer = new InfoObserver(new Handler(), cursor);        //注册一个观察者        contentResolver.registerContentObserver(uri, true, observer);        adapter = new ExampleAdapter(this, cursor, true);        listView.setAdapter(adapter);        listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {            @Override            public boolean onItemLongClick(AdapterView<?> parent, final View view, int position, long id) {                new AlertDialog.Builder(MainActivity.this)                        .setMessage("删除?")                        .setPositiveButton("是", new DialogInterface.OnClickListener() {                            @Override                            public void onClick(DialogInterface dialog, int which) {                                contentResolver.delete(uri, "_id = '" +                                        ((ViewHolder) view.getTag()).id + "'", null);                            }                        })                        .setNegativeButton("否", null)                        .show();                return true;            }        });    }    @Override    protected void onDestroy() {        super.onDestroy();        contentResolver.unregisterContentObserver(observer);    }    private class InfoObserver extends ContentObserver {        private Cursor cursor;        public InfoObserver(Handler handler, Cursor cursor) {            super(handler);            this.cursor = cursor;        }        @Override        public void onChange(boolean selfChange) {            cursor.requery();            adapter.notifyDataSetChanged();        }    }    class ExampleAdapter extends CursorAdapter {        public ExampleAdapter(Context context, Cursor c, boolean autoRequery) {            super(context, c, autoRequery);        }        @Override        public View newView(Context context, Cursor cursor, ViewGroup parent) {            ViewHolder holder = new ViewHolder();            View view = LayoutInflater.from(context).inflate(R.layout.item, null);            holder.tv_name = (TextView) view.findViewById(R.id.name);            holder.tv_sex = (TextView) view.findViewById(R.id.sex);            view.setTag(holder);            return view;        }        @Override        public void bindView(View view, Context context, Cursor cursor) {            ViewHolder holder = (ViewHolder) view.getTag();            holder.id = cursor.getInt(cursor.getColumnIndex(column[0]));            holder.tv_name.setText(cursor.getString(cursor.getColumnIndex(column[1])));            holder.tv_sex.setText(cursor.getString(cursor.getColumnIndex(column[2])));        }    }    class ViewHolder {        int id;        TextView tv_name;        TextView tv_sex;    }}

最后结果大致如下：

获得数据

删除数据

删除数据后

以上是本人对ContentProvider的一些理解，欢迎纠错补充。

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