Wenn listView scroll listView.getChildAt (int index) gibt NULL (Android)

Question

Ich versuche, den Fortschrittsbalken Download in listview und ich habe es getan. Hier ist mein Code AdapterLv.class

public class AdapterPr extends BaseAdapter { 
Activity activity; 
ArrayList<String> listUrl; 
LayoutInflater layoutInflater; 
Clickdownload clickdownload; 
ListView lstView; 
private Handler handler= new Handler(); 
private String NameOfFolder="/DownLoadList1"; 

public AdapterPr(Activity activity, ArrayList<String> listUrl, ListView lstView) { 
    this.activity = activity; 
    this.listUrl = listUrl; 
    layoutInflater = LayoutInflater.from(activity); 
    this.lstView = lstView; 
} 

@Override 
public int getCount() { 
    return listUrl.size(); 
} 

@Override 
public Object getItem(int i) { 
    return listUrl.get(i); 
} 

@Override 
public long getItemId(int i) { 
    return 0; 
} 

@Override 
public View getView(final int i, View view, ViewGroup viewGroup) { 
    View v = layoutInflater.inflate(R.layout.item, viewGroup, false); 
    Button download = (Button) v.findViewById(R.id.download); 
    TextView tvname = (TextView) v.findViewById(R.id.tvName); 
    tvname.setText("Itemt" + i); 
    download.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 

     startDownload(i,listUrl.get(i)); 
     } 
    }); 
    return v; 
} 

private void updateStatus(int index, int Status) { 

    View v = lstView.getChildAt(index - lstView.getFirstVisiblePosition()); 
    ProgressBar progress = (ProgressBar) v.findViewById(R.id.progressBar2); 
    progress.setProgress(Status); 
    TextView txtStatus = (TextView) v.findViewById(R.id.textView); 
    txtStatus.setText("Load : " + String.valueOf(Status) + "%"); 
} 
public String subName(String data) { 
    return data.substring(data.lastIndexOf("/") + 1); 
} 
public void startDownload(final int position,final String urlDownload) { 
    Runnable runnable = new Runnable() { 
     int Status = 0; 
     public void run() { 
      int count = 0; 
      try { 
       URL url = new URL(urlDownload); 
       URLConnection conexion = url.openConnection(); 
       conexion.connect(); 

       int lenghtOfFile = conexion.getContentLength(); 
       Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile); 
       String file_path = Environment.getExternalStorageDirectory().getAbsolutePath() + NameOfFolder; 
       File dir = new File(file_path); 
       if (!dir.exists()) { 
        dir.mkdir(); 
       } 
       File file = new File(dir, subName(urlDownload)); 
       InputStream input = new BufferedInputStream(url.openStream()); 
       OutputStream output = new FileOutputStream(file); 
       byte data[] = new byte[1024]; 
       long total = 0; 
       while ((count = input.read(data)) != -1) { 
        total += count; 
        Status = (int)((total*100)/lenghtOfFile); 
        output.write(data, 0, count); 
        handler.post(new Runnable() { 
         public void run() { 
          updateStatus(position,Status); 
         } 
        }); 
       } 
       output.flush(); 
       output.close(); 
       input.close(); 
      } catch (Exception e) {} 
     } 

    }; 
    new Thread(runnable).start(); 
}} 

Aber wenn ich Listview Scrollen, wenn das Element herunterladen auszublenden (nicht im Bildschirm angezeigt) es zeigen Fehler Nullpointer in

ProgressBar progress = (ProgressBar) v.findViewById(R.id.progressBar2); 

auf Update progressbar. Wie kann ich es beheben? Danke allen!

Answer 1

Statt getFirstVisiblePosition der Verwendung ProgressBar von geklickt ListView Reihe zu bekommen, fügen ProgressBar in startDownload Methode als Parameter und übergeben es an updateStatus:

ändern getView Methode wie:

ProgressBar progress = (ProgressBar) v.findViewById(R.id.progressBar2); 
download.setTag(progress); 
download.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
     ProgressBar pBar=(ProgressBar)view.getTag(); 
     startDownload(i,listUrl.get(i),pBar); 
     } 
    });