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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