如何更新从AsyncTask的列表视图

Question

首先抱歉，如果它的重复，因为我问它，因为无法理解其他问题的任何事情，或者我可以说我不能实现我的情况。 其实我坚持的情况下，我想更新我的ListView从AsyncTask网络更新一个，但现在如何实现它，不知道我尝试了几件事，但无法使其工作。请谁能解释我详细介绍了如何做到这一点，这是我的活动和异步类代码

package app.balaji.sid.listapp; 

    import android.os.AsyncTask; 
    import android.os.Bundle; 
    import android.support.v7.app.ActionBarActivity; 
    import android.util.Log; 
    import android.view.Menu; 
    import android.view.MenuItem; 
    import android.widget.ArrayAdapter; 
    import android.widget.ListView; 

    import it.sauronsoftware.ftp4j.FTPClient; 
    import it.sauronsoftware.ftp4j.FTPFile; 


    public class ListActivity extends ActionBarActivity { 
     ListView lv; 

     @Override 
     protected void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.activity_list); 
      lv=(ListView)findViewById(R.id.listView); 
      String[] values = new String[] { "Item 1", 
        "Item 2", 
        "Item 3 ", 
        "Item 4", 
        "Item 5", 
        "Item 6", 
        "Item 7", 
        "Item 8" 
      }; 
      ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, 
        android.R.layout.simple_list_item_1, android.R.id.text1, values); 
      lv.setAdapter(adapter); 
      new ListFetcher().execute(); 


     } 


     @Override 
     public boolean onCreateOptionsMenu(Menu menu) { 
      // Inflate the menu; this adds items to the action bar if it is present. 
      getMenuInflater().inflate(R.menu.list, menu); 
      return true; 
     } 

     @Override 
     public boolean onOptionsItemSelected(MenuItem item) { 
      // Handle action bar item clicks here. The action bar will 
      // automatically handle clicks on the Home/Up button, so long 
      // as you specify a parent activity in AndroidManifest.xml. 
      int id = item.getItemId(); 
      if (id == R.id.action_settings) { 
       return true; 
      } 
      return super.onOptionsItemSelected(item); 
     } 

     protected class ListFetcher extends AsyncTask<String,String,String>{ 
      String sid; 


      @Override 
      protected String doInBackground(String... params) { 
       String user = "user"; 
       String pass="password"; 
       String host="204.236.238.164"; 

       FTPClient client = new FTPClient(); 

       try { 

        client.connect(host,21); 
        client.login(user, pass); 
        client.setType(FTPClient.TYPE_BINARY); 
        client.changeDirectory("/"); 

        FTPFile[] files = client.list(); 
        String[] fileNames = new String[files.length]; 

        for (int i = 0; i < files.length; i++) 
        { 
         fileNames[i] = files[i].getName(); 
         String logVariable=fileNames[i]; 
         Log.v(sid, logVariable);  // Here i am able to see list in log 
        } 

        }catch (Exception e) 
       { 

        Log.v(sid,e.toString()); 
       } 





       return sid; 
      } 

      protected void onPostExecute() 
      { 

    //i think list should be updated from here but don't know how to do it correctly 
    // i just know i can update my listview by creating a new adapter and assign it to listview but don't know how 
// also i am not able to get the fileNames array here 

      } 



     } 
    } 

Answer 1

这将是比较容易回答，如果你发布链接，愚弄你试过并解释你做了什么不理解。什么是/没有发生也会有所帮助。但是，从我所看到的情况来看，您只需将新的String传递给onPostExecute()，并在那里更新列表和Adapter。

protected void onPostExecute(String result) // get the String you are passing 
{ 

    //i think list should be updated from here but don't know how to do it correctly 
    // I agree. Let's try this 
    if(result != null) // let's make sure you got something 
    { 
     values.add(result); // add the new String to your list 
     adapter.notifyDataSetChanged(); // Hey, Adapter, we've got some new data 

} 

你需要改变你的Array到ArrayList这样的长度可以是动态的。你也会想让这个和你的Adapter成员变量，所以内部类可以看到他们。

public class ListActivity extends ActionBarActivity { 
    ListView lv; 

    // Declare them here 
    ArrayAdapter<String> adapter; 
    ArrayList<String> values = new ArrayList<String>(); 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_list); 
    lv=(ListView)findViewById(R.id.listView); 
    values.add("Item 1"); 
    values.add("Items 2"); 

    adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, 
      android.R.id.text1, values); 
    lv.setAdapter(adapter); 
    new ListFetcher().execute(); 

您没有传递任何你的任务，但要返回一个数组

@Override 
     protected String[] doInBackground(Void... params) { 

protected void onPostExecute(String[] result) 

如果您正在返回一个完全新的价值观，为您的适配器，那么你可以只是更新新的价值。如果您只是添加一些值，那么您可以遍历它们并将它们添加到您的ArrayList并呼叫notifyDataSetChanged()，如上所示。

Answer 2

我刚刚解决了我的问题，所以只是觉得我需要分享它，所以其他面临同样问题的人可以轻松完成。

因此，首先在我的问题，我刚刚声明我的AsyncTask类与字符串参数，但实际上我需要从这里填充我的ListView。

所以我做了什么：

protected class ListFetcher extends AsyncTask<ArrayList,ArrayList,ArrayList>{ 
     String sid; 
     ArrayList list; 



     @Override 
     protected ArrayList doInBackground(ArrayList... params) { 
FTPClient client = new FTPClient(); 

      try { 

       client.connect(host,21); 
       client.login(user, pass); 
       client.setType(FTPClient.TYPE_BINARY); 
       client.changeDirectory("/"); 

       FTPFile[] files = client.list(); 
       String[] fileNames = new String[files.length]; 

       for (int i = 0; i < files.length; i++) 
       { 
        fileNames[i] = files[i].getName(); 
String logVariable=fileNames[i]; 
        Log.v(sid, logVariable); 
        values.add(fileNames[i]); 

       } 

       }catch (Exception e) 
      { 

       Log.v(sid,e.toString()); 
      } 





      return list; 
     } 

     protected void onPostExecute(final ArrayList result)//received result but didn't use it because in my case i don't need it instead of it i just updated my arraylist in doInbackground and updated my ui from here 
     { 


      adapter = new ArrayAdapter<String>(ListActivity.this, android.R.layout.simple_list_item_1, android.R.id.text1, values); 
      ListView listView =(ListView)findViewById(R.id.listView); 

      listView.setAdapter(adapter); 




     }