Android的ContentProvider小记

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：

1. 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
2. 继承 ContentProvider类提供数据访问方式
3. 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：

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：

---

以上是本人对ContentProvider的一些理解，欢迎纠错补充。