在调用notifydatasetchanged（）时，Arrayadapter没有被修改（）

男士我使用一个简单的列表视图。我有两个活动，一个主要和第二个添加朋友在第二个活动中，我将文本框中的朋友的userid并将该行添加到数据库并更新数组列表。当我回到mainactivity时，我调用onResume（）函数中的notifyDataSetChanged（），并且还记录了arraylist值。 Arraylist非常好，并且该行被插入到数据库中，但是listview没有得到更新。我不知道这个问题PLZ的帮助。这里是d代码。在调用notifydatasetchanged（）时，Arrayadapter没有被修改（）

public class VayuActivity extends Activity { 
    /** Called when the activity is first created. */ 
    static boolean first_time=true; 
    ListView friend_list; 
    public static List<String> al; 
    public ArrayAdapter<String> aa; 
    String dummyfriends[]={"prashant","monika","pramod","dhara"}; 
    public static MessengerDataSource mds; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
/*  if(first_time==true) 
     { 
      first_time=false; 
      setContentView(R.layout.registration); 
     } 
     else */ 
      setContentView(R.layout.main); 

     al=new ArrayList<String>(); 
     for(String i:dummyfriends) 
      al.add(i); 

     aa=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, al); 

     friend_list=(ListView) findViewById(R.id.friend_list); 

     friend_list.setAdapter(aa); 

     mds= new MessengerDataSource(getApplicationContext()); 

     mds.open(); 

     System.out.println("I m in oncreate"); 

    } 

    @Override 
    protected void onResume() { 
     // TODO Auto-generated method stub 
     super.onResume(); 

     al=mds.getFriends(); 
     aa.notifyDataSetChanged(); 

     System.out.println("I m in on resume function"); 
     System.out.println("Value of arraylist in on resume fun"+al); 
    } 

    @Override 
    protected void onPause() { 
     // TODO Auto-generated method stub 
     super.onPause(); 
     System.out.println("I m in onpause function"); 
    } 


    @Override 
    public boolean onCreateOptionsMenu(Menu menu) 
    { 


     MenuInflater mi=getMenuInflater(); 
     mi.inflate(R.menu.mainmenu, menu); 

     return true; 





    } 



    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 

     switch(item.getItemId()) 
     { 
     case R.id.add_friend: 
      //Toast.makeText(this, "Add Friend", 2000).show(); 
      Intent i=new Intent(VayuActivity.this,AddFriendActivity.class); 
      startActivity(i); 
      break; 

     case R.id.remove_friend: 
      Toast.makeText(this, "Remove Friend", 2000).show(); 
      break; 

     } 


     return true; 
    } 
} 



package com.pdd.vayu; 

import java.util.ArrayList; 

import android.app.Activity; 
import android.os.Bundle; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.EditText; 

public class AddFriendActivity extends Activity implements OnClickListener{ 

    EditText et; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     // TODO Auto-generated method stub 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.addfriend); 

     et=(EditText) findViewById(R.id.E_friendadd); 

     Button b=(Button) findViewById(R.id.add_friend_button); 
     b.setOnClickListener(this); 
    } 

    public void onClick(View v) { 
     // TODO Auto-generated method stub 
     String userid=et.getText().toString(); 
     //VayuActivity.al.add(f); 
     Friend f=new Friend(); 
     f.setUserid(userid); 
     f.setFname("pratik"); 

     VayuActivity.mds.addFriend(f); 
     VayuActivity.al=(ArrayList<String>) VayuActivity.mds.getFriends(); 
     System.out.println(VayuActivity.al); 
     //VayuActivity.aa.notifyDataSetChanged(); 
    } 
}

数据库类

package com.pdd.vayu; 

import java.util.ArrayList; 
import java.util.List; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 

public class MessengerDataSource { 

    private SQLiteDatabase database; 
    private MyDatabaseHelper mydbh; 

    public static String USER_ID="userid"; 
    public static String F_NAME="fname"; 
    public static String CHAT_COUNT="chat_count"; 

    public static String M_TEXT="mtext"; 
    public static String SENDER="sender"; 
    public static String RECEIVER="receiver"; 
    public static String M_TYPE="type"; 



    public MessengerDataSource(Context c) 
    { 
     mydbh=new MyDatabaseHelper(c); 
    } 

    public void open() 
    { 
     try 
     { 
      database=mydbh.getWritableDatabase(); 
     } 
     catch(Exception e) 
     { 
      System.out.println(e.getLocalizedMessage()); 
     } 
    } 

    public void close() { 
     mydbh.close(); 
    } 

    public void addFriend(Friend f) 

    { 
     ContentValues cv = new ContentValues(); 
     cv.put(USER_ID,f.getUserid()); 
     cv.put(F_NAME, f.getFname()); 
     cv.put(CHAT_COUNT, f.getChat_count()); 

     try 
     { 
      database.insert(MyDatabaseHelper.TABLE_FRIEND, null, cv); 
     } 
     catch(Exception e) 
     { 
      System.out.println("Error while inserting "+e.getLocalizedMessage()); 
     } 

    } 

    public void addMessage(Message m) 

    { 
     ContentValues cv = new ContentValues(); 
     cv.put(M_TEXT, m.getText()); 
     cv.put(SENDER,m.getSender()); 
     cv.put(RECEIVER,m.getReceiver()); 
     cv.put(M_TYPE, m.getType()); 


     database.insert(MyDatabaseHelper.TABLE_MESSAGE, null, cv); 
    } 

    public void deleteFriend(String fname) 
    { 
     database.delete(MyDatabaseHelper.TABLE_FRIEND,F_NAME+"="+fname , null); 

    } 

    public void deleteMessage(String text) 

    { 
     database.delete(MyDatabaseHelper.TABLE_FRIEND,M_TEXT+"="+text , null); 
    } 

    public List<String> getFriends() 

    { 
     List<String> friends= new ArrayList<String>(); 
     Cursor c=null; 
     try 
     { 
     c=database.query(MyDatabaseHelper.TABLE_FRIEND, new String[]{F_NAME}, null, null, null, null,CHAT_COUNT); 
     } 
     catch(Exception e){System.out.println("Error while retrieving frnds list"+e.getLocalizedMessage()); 
     } 

     if(c.moveToFirst()) 
     { 
      do 
      { 
       String friend=c.getString(c.getColumnIndex(F_NAME)); 
       friends.add(friend); 
      } 
      while(c.moveToNext()); 
     } 




     return friends; 
    } 

    public List<String> getMessages(String from) 

    { 
     List<String> messages= new ArrayList<String>(); 

     String where=SENDER+"="+from; 

     Cursor c=database.query(MyDatabaseHelper.TABLE_MESSAGE, new String[]{M_TEXT},where , null, null, null,null); 

     if(c.moveToFirst()) 
     { 
      do 
      { 
       String message=c.getString(c.getColumnIndex(M_TEXT)); 
       messages.add(message); 
      } 
      while(c.moveToNext()); 
     } 


     return messages; 
    } 




}

数据库帮助

package com.pdd.vayu; 

import android.content.Context; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteDatabase.CursorFactory; 
import android.database.sqlite.SQLiteOpenHelper; 

public class MyDatabaseHelper extends SQLiteOpenHelper { 


    public static String TABLE_FRIEND="friend"; 

    public static String TABLE_MESSAGE="message"; 

    public static String CREATE_FRIEND="create table if not exists "+ 
    TABLE_FRIEND+" (userid varchar primary key,fname varchar,chat_count int);"; 

    public static String CREATE_MESSAGE="create table if not exists "+ 
    TABLE_MESSAGE+"(mid integer primary key autoincrement," + 
    "mtext varchar," +"sender varchar , receiver varchar , type varchar)"; 

    //public static String TABLE_FRIENDS="friends"; 

    public static String DB_NAME="MessengerDB.db"; 

    Context context; 


    public MyDatabaseHelper(Context context) { 
     super(context, DB_NAME, null, 1); 
     // TODO Auto-generated constructor stub 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 
     // TODO Auto-generated method stub 

     db.execSQL(CREATE_FRIEND); 
     db.execSQL(CREATE_MESSAGE); 

    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     // TODO Auto-generated method stub 

    } 

}

请帮助

来源

2012-04-11 Pratik

您必须在onresume（）中的arrayadpter中再次设置a1数据。 – Newts 2012-04-11 12:41:38

我只在这一行中创建了al = mds.getFriends（）; – Pratik 2012-04-11 12:45:46

在列表arrayadpter不刷新，如果其更改的数据不重新插入adpter，所以尝试它像创建方法aa = new ArrayAdapter （this，android.R.layout.simple_list_item_1，al）; – Newts 2012-04-11 12:48:15

要使notifyDataSetChanged（）正常工作，您必须使用其添加/删除方法而不是实际列表将该对象添加到ArrayAdapter本身。

你的onResume应该是这个样子：

@Override 
protected void onResume() { 
    // TODO Auto-generated method stub 
    super.onResume(); 

    //al=mds.getFriends(); 
    aa.clear(); 
    aa.addAll(mds.getFriends()); 
    aa.notifyDataSetChanged(); 

    System.out.println("I m in on resume function"); 
    System.out.println("Value of arraylist in on resume fun"+al); 
}

一个ArrayAdapter开始创建时列表的副本，所以当调用notifyDataSetChanged它只是看起来它自己的副本，而不是源列表。

来源

2012-04-11 14:10:59 Freddroid

你必须尝试notifyDataSetChanged（）方法，这样

有时我当你没有在adpter中加载新数据时不加载数据，所以在调用这个函数之前，你必须在onresume（）方法中的arrayadpter中加载数据，而不是onCreate（）方法。

public void refresh() 
    { 

     mHandler.postDelayed(new Runnable() { 

      @Override 
      public void run() { 

       ((EfficentAdapter)list.getAdapter()).notifyDataSetChanged(); 
       }   
     }, 100); 

    }

来源

2012-04-11 12:55:09 Newts

在调用notifydatasetchanged（）时，Arrayadapter没有被修改（）

回答

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