android中第四大组件ContentProvider

第四大组件ContentProvider

功能：数据共享

     按照文件路径和格式

无论哪种数据持久化方法，数据共享的接口统一为ContentProvider

系统自带应用的数据

通讯：拨号 短信 联系人

多媒体：音乐 视频 图片 拍照

其他：Home Launcher

一、新建ex0814_contentprovider项目

ContentProvider负责组织应用程序的数据，向其他应用程序提供数据。

清单配置如下：（增加属性authorities）

<application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <provider
            android:name="com.example.ex0814_contentprovider.MyContentProvider"
            android:authorities="com.example.provider.student"
            android:enabled="true"
            android:exported="true" >
        </provider>
    </application>

代码如下：

//ex0814_contentresolver项目和ex0814_contentprovider项目。
public class MyContentProvider extends ContentProvider
{//创建一个数据共享接口ContentProvider，让其他的应用可以对他进行增删改查
    private SQLiteDatabase mDb;
    private static final String TABLE_NAME = "student";
    private static final String CULUMN_NAME_NAME = "name";
    private static final String CULUMN_NAME_PHONE = "phone";
//    步骤：
//    1.新建一个项目，删除Activity和清单中的  Activity的配置
//    2.新建android object，选择contentprovider，并设置 authorities属性
//    3.字符串建议：packagename + provider + 数据功能名
//    4.在provider类中，创建MySqliteOpenhelper的内部类
//    5.在onCreate（）里面获取SQLiteDatabase对象
//    6.实现增删改查的方法
    public MyContentProvider()
    {
    }
    //重写增删改查的方法
    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs)
    {
        int delete = mDb.delete(TABLE_NAME, selection, selectionArgs);
        return delete;
    }
    @Override
    public String getType(Uri uri)
    {
        // TODO: Implement this to handle requests for the MIME type of the data
        // at the given URI.
        throw new UnsupportedOperationException("Not yet implemented");
    }
    @Override
    public Uri insert(Uri uri, ContentValues values)
    {//values由ex0814_contentresolver项目传来
       long insert = mDb.insert(TABLE_NAME, null, values);
       Uri withAppendedId = ContentUris.withAppendedId(uri, insert);
       return withAppendedId;
    }
    @Override
    public boolean onCreate()
    {
        MySqliteOpenhelper openhelper = new MySqliteOpenhelper(getContext(), 1);
        mDb = openhelper.getWritableDatabase();
        return false;
    }
    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder)
    {
        Cursor query = mDb.query(TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder);
        return query;
    }
    @Override
    public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs)
    {
        int update = mDb.update(TABLE_NAME, values, selection, selectionArgs);
        return update;
    }
    public class MySqliteOpenhelper extends SQLiteOpenHelper
    {
        public MySqliteOpenhelper(Context context, int version)
        {
            super(context, "cuijing.db", null, version);
            // TODO Auto-generated constructor stub
        }
        @Override
        public void onCreate(SQLiteDatabase db)
        {//创建表，一运行，会去检查是否有表，如果已经有了，或者版本号更新，都不会再执行onCreate（）;
           Log.e("MySqliteOpenhelper", "onCreate");
            db.execSQL("CREATE TABLE student(_id INTEGER PRIMARY KEY AUTOINCREMENT,name VARCHAR(20),phone VARCHAR(20))");
        }
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
        {//如果已经有表存在，并且版本号有更新，就会执行onUpgrade（）；
           Log.e("MySqliteOpenhelper", "onUpgrade");
            db.execSQL("ALTER TABLE student ADD COLUMN weight INTEGER");
        }
    }
}

二、新建ex0814_contentresolver项目

   使用其他应用的Provider的方法：

   1. getContentResolver()

   2. resolver.query(uri, )

ContentResolver则负责获取ContentProvider提供的数据，修改/添加/删除更新数据等。

代码如下：

public class MainActivity extends Activity implements OnClickListener
{//ex0814_contentresolver查询ex0814_contentprovider项目的数据库，通过ex0814_contentprovider提供的provider共享接口。
   private EditText mEt_name;
   private EditText mEt_phone;
   private ContentResolver contentResolver;
   private TextView textView;
   private ListView listView;
   private static final String TABLE_NAME = "student";
   private static final String CULUMN_NAME_NAME = "name";
   private static final String CULUMN_NAME_PHONE = "phone";
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        contentResolver = getContentResolver();
        findViewById(R.id.btn_baocun).setOnClickListener(this);
        findViewById(R.id.btn_delete).setOnClickListener(this);
        findViewById(R.id.btn_selector).setOnClickListener(this);
        findViewById(R.id.btn_update).setOnClickListener(this);
        listView = (ListView) findViewById(R.id.listView1);
        mEt_name = (EditText) findViewById(R.id.et_name);
        mEt_phone = (EditText) findViewById(R.id.et_phone);
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
    @Override
    public void onClick(View v)
    {
        switch (v.getId())
        {
            case R.id.btn_baocun:
                insert();
                break;
            case R.id.btn_delete:
                delete();
                break;
            case R.id.btn_selector:
                selector();
                break;
            case R.id.btn_update:
                update();
                break;
            default:
                break;
        }
    }
    private void update()
    {//修改
        Editable et_name = mEt_name.getText();
        Editable et_phone = mEt_phone.getText();
        ContentValues values = new ContentValues();
        values.put(CULUMN_NAME_PHONE, et_phone.toString());//修改号码
        contentResolver.update(Uri.parse("content://com.example.provider.student"), values, "name=?", new String[]{et_name.toString()});//根据名字修改号码
    }
    private void selector()
    {//查询
        Cursor cursor = contentResolver.query(Uri.parse("content://com.example.provider.student"), null, null, null, null);
        String[] from = {CULUMN_NAME_NAME,CULUMN_NAME_PHONE};
        int[] to = {android.R.id.text1,android.R.id.text2};
//       使用 SimpleCursorAdapter，要把创建表中的自增ID修改成_id
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(MainActivity.this, android.R.layout.simple_list_item_2, cursor, from, to);
        listView.setAdapter(adapter);
    }
    private void delete()
    {//删除
        Editable et_name = mEt_name.getText();
        contentResolver.delete(Uri.parse("content://com.example.provider.student"),  "name=?", new String[]{et_name.toString()});//删除的是数据库里editext显示为name的数据
    }
    private void insert()
    {//把ex0814_contentresolver项目里editext的内容插入到ex0814_contentprovider项目的数据库（database）里
        ContentValues values = new ContentValues();
        Editable et_name = mEt_name.getText();
        Editable et_phone = mEt_phone.getText();
        values.put("name", et_name.toString());
        values.put("phone", et_phone.toString());
        contentResolver.insert(Uri.parse("content://com.example.provider.student"), values);//uri格式必须以content：//开头，uri内容为ex0814_contentprovider的anthoritise（属性）
    }
}