Android 自定义ContentProvider简单实例

Android 自定义ContentProvider简单实例

Android允许我们定义自己的的ContentProvider对象来共享数据，练练手，简单来实现一下。

要使用ContentProvider来操作数据，必须要有保存数据的场所。可以使用文件或SQLite数据库的方式来保存数据，通常使用SQLite数据库。

1，创建一个数据库帮助类，归根结底都是它在操作数据库。代码如下：

package com.njue; 
 
import android.content.Context; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteDatabase.CursorFactory; 
import android.database.sqlite.SQLiteOpenHelper; 
 
public class DBManager extends SQLiteOpenHelper { 
public static final String myProvider_table_name="myProvider_table_name"; 
String sql="create table myProvider_table_name(id integer,name text)"; 
  public DBManager(Context context) { 
    super(context, "myPrivoder.db", null, 1); 
    // TODO Auto-generated constructor stub 
  } 
 
  @Override 
  public void onCreate(SQLiteDatabase arg0) { 
    // TODO Auto-generated method stub 
   arg0.execSQL(sql); 
  } 
 
  @Override 
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    // TODO Auto-generated method stub 
 
  } 
 
} 

2，创建一个myProvider类，该类继承ContentProvider，实现其抽象方法来操作数据库，该类引用DBManager类来获得数据库实例。

package com.njue; 
 
import android.content.ContentProvider; 
import android.content.ContentValues; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.net.Uri; 
 
public class myProvider extends ContentProvider { 
  DBManager dbHelper; 
  @Override 
  public int delete(Uri arg0, String arg1, String[] arg2) { 
    // TODO Auto-generated method stub 
    SQLiteDatabase db=dbHelper.getWritableDatabase(); 
    int id=db.delete(DBManager.myProvider_table_name, arg1, arg2); 
    if(id!=0)return id; 
    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 
    SQLiteDatabase db=dbHelper.getWritableDatabase(); 
    db.insert(DBManager.myProvider_table_name, "id", values); 
    return null; 
  } 
 
  @Override 
  public boolean onCreate() { 
    // TODO Auto-generated method stub 
    dbHelper=new DBManager(getContext()); 
    return true; 
  } 
 
  @Override 
  public Cursor query(Uri uri, String[] projection, String selection, 
      String[] selectionArgs, String sortOrder) { 
    // TODO Auto-generated method stub 
    SQLiteDatabase db=dbHelper.getWritableDatabase(); 
    Cursor c=db.query(DBManager.myProvider_table_name,projection, selection, selectionArgs, null, null, sortOrder); 
    return c; 
  } 
 
  @Override 
  public int update(Uri uri, ContentValues values, String selection, 
      String[] selectionArgs) { 
    // TODO Auto-generated method stub 
    SQLiteDatabase db=dbHelper.getWritableDatabase(); 
    int id=db.update(DBManager.myProvider_table_name, values, selection, selectionArgs); 
    if(id!=0)return id; 
    return 0; 
  } 
 
} 

3，ContextProvider必须声明才能使用，因此，需要在AndroidManifest.xml配置文件中声明。声明很简单，需要类名称和授权名称两个属性。

<provider android:name="myProvider" 
    android:authorities="com.njue.myProvider" /> 

 到这里，我们自定义的ContentProvider就完成了。我们可以在Eclipse中的File Explorer 窗口中看到自定义的ContentProvider

 4，简单测试

package com.njue; 
 
import android.app.Activity; 
import android.content.ContentResolver; 
import android.content.ContentValues; 
import android.database.Cursor; 
import android.net.Uri; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 
 
public class Content_providerActivity extends Activity { 
  /** Called when the activity is first created. */ 
   Uri uri; 
   String AUTHORITY="content://com.njue.myProvider/myProvider_table_name"; 
   ContentResolver cr; 
   EditText input; 
   Button insert; 
   TextView show; 
  @Override 
  public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    input=(EditText)findViewById(R.id.input); 
    insert=(Button)findViewById(R.id.insert); 
    show=(TextView)findViewById(R.id.show); 
    uri=uri.parse(AUTHORITY); 
    cr=this.getContentResolver(); 
    insert.setOnClickListener(new Button.OnClickListener(){ 
 
      @Override 
      public void onClick(View v) { 
        // TODO Auto-generated method stub 
         ContentValues values=new ContentValues(); 
          values.put("name", input.getText().toString()); 
          cr.insert(uri, values); 
          Cursor c=cr.query(uri, null, null, null, null); 
          show.setText(""); 
          c.moveToFirst(); 
          while(c.moveToNext()){ 
           show.append(c.getString(1)+"\r\n"); 
          } 
          input.setText(""); 
      }}); 
     
  } 
} 

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