ContentProvider

在 Android中，对于数据的存贮，有几种方式，有文件方式，有文件式数据库方式,网络数据,Android自带了一个SQLite数据库，做嵌入开发的人对这个跨平台的本地文件数据库一定不会陌生，在Android对于数据的访问，提出了新的方式，ContentProvider方式，我们首先来看看SQLite在 Android中的使用，在Android中有最简单的使用方式，就是利Context对象的openorCreateDatabase
我们来看看一段代码：

import android.app.Activity;import android.content.Intent;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.widget.TextView;public class DBActivity extends Activity { private SQLiteDatabase mdb = null;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        initDatabase();        setContentView(R.layout.main);            }    @Override public boolean onCreateOptionsMenu(Menu menu) {  // TODO Auto-generated method stub  super.onCreateOptionsMenu(menu);     menu.add(1, Menu.FIRST +1, 1, "GetName");    menu.add(1, Menu.FIRST +2, 2, "Test");     return true;   }        public boolean onOptionsItemSelected(MenuItem item) {  // TODO Auto-generated method stub  super.onOptionsItemSelected(item);  switch (item.getItemId())  {   case Menu.FIRST+ 1:   {    TextView tv = (TextView)this.findViewById(R.id.view_main);    tv.setText(this.getName());    break;   }   case Menu.FIRST + 2:   {    this.setTitle("Del Item...");    break;   }     }  return true; }        private void initDatabase()    {     mdb = this.openOrCreateDatabase("dbfile", 0, null);     String sql_create = "create table test (id int, name TEXT)";     mdb.execSQL(sql_create);     String sql_insert = "insert into test(id, name) values(3, 'name3')";     mdb.execSQL(sql_insert);    }    private String getName()    {     String name = null;          Cursor cur = mdb.rawQuery("select * from test", null);     cur.moveToFirst();     while (!cur.isLast())     {      name = name  + cur.getString(1)+ "\r\n";      cur.moveToNext();     }     return name;    }}

我们再来看看单独使用SQLiteOpenHelper方式：
先由SQLiteOpenHelper继承一个数据库操作类，其中onCreate, onUpgrade必须重载并实现，

import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;public class DatabaseHelper extends SQLiteOpenHelper { @Override public void onCreate(SQLiteDatabase db) {  // TODO Auto-generated method stub   } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {  // TODO Auto-generated method stub   } public DatabaseHelper(Context ct,String dbName) {   super(ct,dbName,null,1);   }  public boolean insert(String insert) {  this.getWritableDatabase().execSQL(insert);  return true; } public boolean update(String update) {  this.getWritableDatabase().execSQL(update);  return true; } public boolean delete(String del) {  this.getWritableDatabase().execSQL(del);  return true; } public Cursor query(String query) {  Cursor cur = this.getReadableDatabase().rawQuery(query, null);  return cur; }}

再创建一个使用者（消费者）

import android.app.Activity;import android.content.Intent;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.widget.TextView;public class DBActivity extends Activity { private SQLiteDatabase mdb = null; private DatabaseHelper helper = null;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        initDatabase();        setContentView(R.layout.main);            }    @Override public boolean onCreateOptionsMenu(Menu menu) {  // TODO Auto-generated method stub  super.onCreateOptionsMenu(menu);     menu.add(1, Menu.FIRST +1, 1, "GetName");    menu.add(1, Menu.FIRST +2, 2, "Test");     return true;   }        public boolean onOptionsItemSelected(MenuItem item) {  // TODO Auto-generated method stub  super.onOptionsItemSelected(item);  switch (item.getItemId())  {   case Menu.FIRST+ 1:   {    TextView tv = (TextView)this.findViewById(R.id.view_main);    tv.setText(this.getName());    break;   }   case Menu.FIRST + 2:   {    this.setTitle("Del Item...");    break;   }     }  return true; }        private void initDatabase()    {     helper = new DatabaseHelper(this,"dbfile");     //mdb = this.openOrCreateDatabase("dbfile", 0, null);     //String sql_create = "create table test (id int, name TEXT)";     //mdb.execSQL(sql_create);     String sql_insert = "insert into test(id, name) values(55, 'namexx')";     //mdb.execSQL(sql_insert);     helper.insert(sql_insert);    }    private String getName()    {     String name = null;       //mdb = helper.getReadableDatabase();     Cursor cur = helper.query("select * from test");     cur.moveToFirst();     do     {      name = name  + cur.getString(1)+ "\n";                 } while(cur.moveToNext());                return name;    }}

在来看看使用ContentProvider

import android.content.ContentProvider;import android.content.ContentValues;import android.database.Cursor;import android.net.Uri;import android.widget.Toast;public class TestProvider extends ContentProvider {    private DatabaseHelper mdbHelper = null;    final static String TABLE_NAME = "test"; @Override public int delete(Uri arg0, String arg1, String[] arg2) {  mdbHelper.getWritableDatabase().delete(TABLE_NAME, arg1, arg2);  return 0; } @Override public String getType(Uri uri) {  // TODO Auto-generated method stub  return null; } @Override public Uri insert(Uri uri, ContentValues values) {  // TODO Auto-generated method stub  mdbHelper.getWritableDatabase().insert(TABLE_NAME, "", values);  return null; } @Override public boolean onCreate() {  // TODO Auto-generated method stub  mdbHelper = new DatabaseHelper(this.getContext(), "dbfile");  return true; } @Override public Cursor query(Uri uri, String[] projection, String selection,   String[] selectionArgs, String sortOrder) {  Cursor cur = mdbHelper.getReadableDatabase().query(TABLE_NAME,projection,selection,null,null,null, null);  Toast.makeText(this.getContext(), "test Cur!", Toast.LENGTH_SHORT);  return cur; } @Override public int update(Uri uri, ContentValues values, String selection,   String[] selectionArgs) {  mdbHelper.getWritableDatabase().update(TABLE_NAME, values, selection, null);  return 0; }}

老规矩,AndroidManifest.xml来定义这个Provider

这里的android:authorities = "com.my.provider"是标识这个ContentProvider，调用者可以根据这个标识来找到它，
我们组合一个能找到它的Uri,
public class ProviderConst {
public static final Uri MY_TEST_URI = Uri.parse("content://com.my.provider/test");

}

content 指的是内容提供者ContentProvider。
//com.my.provider映射到我们已定义的那个ContentProvider标识
/test这个作为一个参数，传给ContentProvider，可以根据这个参数来决定操作目标，比如数据库中的哪张表，文件中的那一部分数据等。

我们来操作这个内容提供者：

private String getName()    {     String name = null;           Cursor cur = this.getContentResolver().query(ProviderConst.MY_TEST_URI,new String[]{"id","name"},null, null, null);     if (cur == null)      return null;     cur.moveToFirst();     do     {      name = name  + cur.getString(1)+ "\n";                 } while(cur.moveToNext());                return name;    }

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