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
<provider android:label="test_provider" android:authorities="com.my.provider" android:name="TestProvider">
    </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;
    }

 

评论

1 楼 缺氧小老鼠 2011-09-15  

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