ListView每次創建片段時都會顯示重複的數據

Question

這裏是我的片段的代碼，我在asynctask中訪問一個web服務來獲取數據並在列表中顯示，我也懶加載圖像。當片段創建爲第一次輸出是正確的，它會在列表中顯示7個項目，問題是當片段在被銷燬後重新創建數據被重複時，即如果它第二次啓動，則列表顯示14個項目（早期7個項目7次再次被提取），每當它重新創建時，都會發生這種情況。列表中的項目比以前多了7個。儘管在On destroy中，我清除了適配器的數據，而adapter.getCount（）顯示爲0，但仍然存在此問題。

public class ServiceCarListFragment extends Fragment { 

private String url; 
private ArrayList<CarDetail> carDetailList = new ArrayList<CarDetail>(); 
private CarListAdapter adapter; 
private ListView mList ; 
private ProgressDialog progressDialog; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    super.onCreate(savedInstanceState); 
    Log.d("Services", "On Create"); 
    url = getActivity().getIntent().getStringExtra("url"); 
    adapter = new CarListAdapter(getActivity() , carDetailList); 
    new DownloadCarDetail().execute(url); 

} 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
     Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    Log.d("Services", "On CreateView"); 
    View v = inflater.inflate(R.layout.fragment_service_car_list,  container,false); 
    mList = (ListView)v.findViewById(R.id.list); 
    mList.setAdapter(adapter);  
    return v; 
} 

class DownloadCarDetail extends AsyncTask<String, String, ArrayList<CarDetail>>{ 



    @Override 
    protected void onPreExecute() { 
     // TODO Auto-generated method stub 
     super.onPreExecute(); 
     progressDialog = ProgressDialog.show(getActivity(), null, "Loading...",true); 

    } 

    @Override 
    protected ArrayList<CarDetail> doInBackground(String... params) { 
     // TODO Auto-generated method stub 
     ArrayList<CarDetail> carDetailList = JsonParser.parseJson(params[0]); 
     return carDetailList; 
    } 

    @Override 
    protected void onPostExecute(ArrayList<CarDetail> carDetailList) { 
     // TODO Auto-generated method stub 
     //ServiceCarListFragment.this.carDetailList = carDetailList; 
     //adapter = new CarListAdapter(getActivity(),ServiceCarListFragment.this.carDetailList); 
     //mList.setAdapter(adapter); 
     progressDialog.dismiss(); 
     ServiceCarListFragment.this.carDetailList.addAll(carDetailList); 
     adapter.notifyDataSetChanged(); 
     for (CarDetail car : carDetailList) { 
      // START LOADING IMAGES FOR EACH STUDENT 
      car.loadImage(adapter); 

    } 

} 

} 

@Override 
public void onDestroy() { 
    // TODO Auto-generated method stub 
    super.onDestroy(); 
    carDetailList.clear(); 
    adapter.notifyDataSetChanged(); 
    Log.d("Services", String.valueOf(adapter.getCount())); 
} 

@Override 
public void onDestroyView() { 
    // TODO Auto-generated method stub 
    super.onDestroyView(); 
    Log.d("Services", "On DestroyView"); 
} 

@Override 
public void onDetach() { 
    // TODO Auto-generated method stub 
    super.onDetach(); 
    Log.d("Services", "On Detach"); 
} 

@Override 
public void onAttach(Activity activity) { 
    // TODO Auto-generated method stub 
    super.onAttach(activity); 
    Log.d("Services", "On Attach"); 
} 

} 

這是我使用

public class CarListAdapter extends BaseAdapter { 

private ArrayList<CarDetail> items = new ArrayList<CarDetail>(); 
private Context context; 


public CarListAdapter(Context context , ArrayList<CarDetail> items) { 
    super(); 
    this.context = context; 
    this.items = items; 

} 

@Override 
public int getCount() { 
    // TODO Auto-generated method stub 
    return items.size(); 
} 

@Override 
public Object getItem(int position) { 
    // TODO Auto-generated method stub 
    return items.get(position); 
} 

@Override 
public long getItemId(int position) { 
    // TODO Auto-generated method stub 
    return position; 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    // TODO Auto-generated method stub 
    Log.d("Inside", "GetView"); 
    LayoutInflater mInflater = (LayoutInflater)context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE); 
    ViewHolder holder = null; 
    CarDetail car = items.get(position); 

    if (convertView == null) { 
      convertView = mInflater.inflate(R.layout.car_list_row, parent , false); 
      holder = new ViewHolder(); 
      holder.tvCarName = (TextView) convertView.findViewById(R.id.tvCarName); 
      holder.tvDailyPriceValue = (TextView) convertView.findViewById(R.id.tvWeeklyPriceValue); 
      holder.tvWeeklyPriceValue = (TextView) convertView.findViewById(R.id.tvWeeklyPriceValue); 
      holder.imgCar = (ImageView) convertView.findViewById(R.id.imgCar); 
      convertView.setTag(holder); 
    } 
    else { 
      holder = (ViewHolder) convertView.getTag(); 
     } 

    holder.tvCarName.setText(car.getCarName()); 
     if (car.getImage() != null) { 
      holder.imgCar.setImageBitmap(car.getImage()); 
     } else { 
       // MY DEFAULT IMAGE 
      holder.imgCar.setImageResource(R.drawable.ic_action_call); 
     } 

    return convertView; 
} 

static class ViewHolder { 

      TextView tvCarName; 
      TextView tvDailyPriceValue; 
      TextView tvWeeklyPriceValue; 
      ImageView imgCar; 
     } 

} 

這個自定義適配器模型類

public class CarDetail { 

private String carId; 
private String carName; 
private String imageUrl; 
private String thumbUrl; 
private String dailyPrice; 
private String weeklyPrice; 
private String weekendPrice; 
private String deposit; 
private String minimumAge; 
private String color; 
private String make; 
private String location; 
private String bodyType; 
private String fuelType; 
private String transmission; 
private String carType; 
private String model; 
private String description; 
private Bitmap image; 
private Bitmap thumbImage; 
private CarListAdapter carAdapter; 

public CarDetail() { 
    super(); 
    // TODO Auto-generated constructor stub 
} 

public CarDetail(String carId, String carName, String imageUrl, 
     String thumbUrl, String dailyPrice, String weeklyPrice, 
     String weekendPrice, String deposit, String minimumAge, 
     String color, String make, String location, String bodyType, 
     String fuelType, String transmission, String carType, String model, 
     String description) { 
    super(); 
    this.carId = carId; 
    this.carName = carName; 
    this.imageUrl = imageUrl; 
    this.thumbUrl = thumbUrl; 
    this.dailyPrice = dailyPrice; 
    this.weeklyPrice = weeklyPrice; 
    this.weekendPrice = weekendPrice; 
    this.deposit = deposit; 
    this.minimumAge = minimumAge; 
    this.color = color; 
    this.make = make; 
    this.location = location; 
    this.bodyType = bodyType; 
    this.fuelType = fuelType; 
    this.transmission = transmission; 
    this.carType = carType; 
    this.model = model; 
    this.description = description; 

    // TO BE LOADED LATER - OR CAN SET TO A DEFAULT IMAGE 
    this.image = null; 
    this.thumbImage = null; 
} 

public String getCarId() { 
    return carId; 
} 

public void setCarId(String carId) { 
    this.carId = carId; 
} 

public String getCarName() { 
    return carName; 
} 

public void setCarName(String carName) { 
    this.carName = carName; 
} 

public String getImageUrl() { 
    return imageUrl; 
} 

public void setImageUrl(String imageUrl) { 
    this.imageUrl = imageUrl; 
} 

public String getThumbUrl() { 
    return thumbUrl; 
} 

public void setThumbUrl(String thumbUrl) { 
    this.thumbUrl = thumbUrl; 
} 

public String getDailyPrice() { 
    return dailyPrice; 
} 

public void setDailyPrice(String dailyPrice) { 
    this.dailyPrice = dailyPrice; 
} 

public String getWeeklyPrice() { 
    return weeklyPrice; 
} 

public void setWeeklyPrice(String weeklyPrice) { 
    this.weeklyPrice = weeklyPrice; 
} 

public String getWeekendPrice() { 
    return weekendPrice; 
} 

public void setWeekendPrice(String weekendPrice) { 
    this.weekendPrice = weekendPrice; 
} 

public String getDeposit() { 
    return deposit; 
} 

public void setDeposit(String deposit) { 
    this.deposit = deposit; 
} 

public String getMinimumAge() { 
    return minimumAge; 
} 

public void setMinimumAge(String minimumAge) { 
    this.minimumAge = minimumAge; 
} 

public String getColor() { 
    return color; 
} 

public void setColor(String color) { 
    this.color = color; 
} 

public String getMake() { 
    return make; 
} 

public void setMake(String make) { 
    this.make = make; 
} 

public String getLocation() { 
    return location; 
} 

public void setLocation(String location) { 
    this.location = location; 
} 

public String getBodyType() { 
    return bodyType; 
} 

public void setBodyType(String bodyType) { 
    this.bodyType = bodyType; 
} 

public String getFuelType() { 
    return fuelType; 
} 

public void setFuelType(String fuelType) { 
    this.fuelType = fuelType; 
} 

public String getTransmission() { 
    return transmission; 
} 

public void setTransmission(String transmission) { 
    this.transmission = transmission; 
} 

public String getCarType() { 
    return carType; 
} 

public void setCarType(String carType) { 
    this.carType = carType; 
} 

public String getModel() { 
    return model; 
} 

public void setModel(String model) { 
    this.model = model; 
} 

public String getDescription() { 
    return description; 
} 

public void setDescription(String description) { 
    this.description = description; 
} 

public Bitmap getImage() { 
    return image; 
} 

public void setImage(Bitmap image) { 
    this.image = image; 
} 

public Bitmap getThumbImage() { 
    return thumbImage; 
} 

public void setThumbImage(Bitmap thumbImage) { 
    this.thumbImage = thumbImage; 
} 

public void loadImage(CarListAdapter carAdapter) { 
     // HOLD A REFERENCE TO THE ADAPTER 
     this.carAdapter = carAdapter; 
     if (thumbUrl != null && !thumbUrl.equals("")) { 
      new ImageLoadTask().execute(thumbUrl); 
     } 
} 

    // ASYNC TASK TO AVOID CHOKING UP UI THREAD 
    private class ImageLoadTask extends AsyncTask<String, String, Bitmap> { 

     @Override 
     protected void onPreExecute() { 
      Log.i("ImageLoadTask", "Loading image..."); 
     } 

     // PARAM[0] IS IMG URL 
     protected Bitmap doInBackground(String... param) { 
      Log.i("ImageLoadTask", "Attempting to load image URL: " + param[0]); 
      try { 
       Bitmap b = JsonParser.downloadBitmap(param[0]); 
       return b; 
      } catch (Exception e) { 
       e.printStackTrace(); 
       return null; 
      } 
     } 

     protected void onProgressUpdate(String... progress) { 
      // NO OP 
     } 

     protected void onPostExecute(Bitmap ret) { 
      if (ret != null) { 
       Log.i("ImageLoadTask", "Successfully loaded " + carName + " image"); 
       image = ret; 
       if (carAdapter != null) { 
        // WHEN IMAGE IS LOADED NOTIFY THE ADAPTER 
        carAdapter.notifyDataSetChanged(); 
       } 
      } else { 
       Log.e("ImageLoadTask", "Failed to load " + carName + " image"); 
      } 
     } 
    } 

Answer 1

您需要在下次調用異步方法之前清除ArrayList數據。 在你的情況下，它將是carDetailLis.clear()new DownloadCarDetail().execute(url);或只是檢查流量並清除它。

Answer 2

我建議你修改

ServiceCarListFragment.this.carDetailList.addAll(carDetailList); 

在

ServiceCarListFragment.this.carDetailList = new ArrayList... 
carDetailList.addAll 

而且您應該驗證carDetailList的長度在多次調用服務器之後是否相同。