奇怪的NullPointerException我不希望它：

Question

所以交易是這樣的，我昨天發佈的應用程序商店，而我得到的空指針異常很多我ArrayAdapter：

適配器：

public class NewVenuesListRecyclingAdapterWithVenueObjects extends ArrayAdapter<Venue> 
{ 
.... 
public NewVenuesListRecyclingAdapterWithVenueObjects(Context context, int textViewResourceId, List<Venue> items) 
{ 
.... 
} 

public View getView(final int position, View convertView, ViewGroup parent) 
{ 
    ViewHolder holder; 
    View currentView = convertView; 

    if(null == currentView) 
    { 
     LayoutInflater inflater = (LayoutInflater) activity.getSystemService(Activity.LAYOUT_INFLATER_SERVICE); 
     .... 
    } 
    else 
    { 
     holder = (ViewHolder)currentView.getTag(); 
    } 

    .... 
    if (UserLocation.instance.getLastKnownLocation() == null) { 
     holder.venueDistance.setText(""); 
     ((ViewGroup) currentView).requestLayout(); 
    } else { 
     // cups#202: `venueDistance` might be null in case we recycle a list item 
     // this is not really a fix, but should relatively okay (the distance will just not appear). 
     if (venuesList.get(position).getDistance() != 0.0f) { 
      holder.venueDistance.setVisibility(View.VISIBLE); 
      holder.venueDistanceUnit.setVisibility(View.VISIBLE); 
      if(FileAccessUtil.instance.getStringProperty(Consts.DISTANCE_UNIT).equals(Consts.DISTANCE_UNIT_KILOMETER)) 
      { 
       holder.venueDistance.setText(formatDistanceKilometer(activity, venuesList.get(position).getDistance())); 
       holder.venueDistanceUnit.setText(context.getResources().getString(R.string.distance_km)); 
       CupsLog.d(TAG, "chosen distance unit is km"); 

      } 
      else if(FileAccessUtil.instance.getStringProperty(Consts.DISTANCE_UNIT).equals(Consts.DISTANCE_UNIT_MILE)) 
      { 
       holder.venueDistance.setText(formatDistanceMiles(activity, venuesList.get(position).getDistance())); 
       holder.venueDistanceUnit.setText(context.getResources().getString(R.string.distance_mile)); 
       CupsLog.d(TAG, "chosen distance unit is mile"); 
      } 
     } 
    } 
    return currentView; 
} 

static class ViewHolder 
{ 
    TextView venueName; 
    TextView venueAddress; 
    TextView venueDistance; 
    TextView venueDistanceUnit; 
    ImageView venueImage; 
    ImageView venuebackImage; 
    ImageView venueMapIcon; 
    ImageView venueFavoriteIcon; 
    ProgressBar spinner; 
} 
} 

該行給我的例外是：

if(FileAccessUtil.instance.getStringProperty(Consts.DISTANCE_UNIT).equals(Consts.DISTANCE_UNIT_KILOMETER)) 

此行determins如果用戶希望以公里或英里顯示distnace根據他的選擇在設置頁面，FileAccessUtil是一個輔助類，其中包括有那些方法：

public void init(Context context) { 
    sharedPreferences = context.getSharedPreferences(Consts.PREFERENCSE_FILE_NAME, Activity.MODE_PRIVATE); 
} 

public String getStringProperty(String key) { 
    String res = null; 
    if (sharedPreferences != null) { 
     res = sharedPreferences.getString(key, null); 
    } 
    return res; 
} 

public void setStringProperty(String key, String value) { 
    if (sharedPreferences != null) { 
     SharedPreferences.Editor editor = sharedPreferences.edit(); 
     editor.putString(key, value); 
     editor.commit(); 
     CupsLog.i(TAG, "Set " + key + " property = " + value); 
    } 
} 

的帕塞爾的最終和平是我在Application類中設置該屬性：

public class App extends Application 
{ 
.... 

    public void onCreate() 
    { 
     super.onCreate(); 
     appObjInstance = this; 

     FileAccessUtil.instance.init(this); 
     if (FileAccessUtil.instance.getStringProperty(Consts.DISTANCE_UNIT) == null) 
     { 
      FileAccessUtil.instance.setStringProperty(Consts.DISTANCE_UNIT, Consts.DISTANCE_UNIT_KILOMETER); 
     } 
     .... 
    } 
} 

我可以ofcourse檢查空獲得期望之前，但我想，以避免會在ListView每個視圖運行適配器的內部此項檢查。

有人知道可能是什麼問題嗎？

Answer 1

如果你要這樣寫代碼：

if(FileAccessUtil.instance.getStringProperty(Consts.DISTANCE_UNIT).equals(Consts.DISTANCE_UNIT_KILOMETER)) 

然後，你需要確保getStringProperty(...)永遠不能返回null：

public String getStringProperty(String key) { 
    String res = ""; 
    if (sharedPreferences != null) { 
     res = sharedPreferences.getString(key, null); 
    } 
    return res; 
} 

的問題是，當你想到的Consts.DISTANCE_UNIT將出現在用戶的設置中（當你說這個問題不會發生在你身上時，我相信你，可能是因爲它在您的設置中爲是），但事實上並非如此。也許根本問題在於你的安裝，誰知道？但我懷疑你應該修改getStringProperty(...)返回一個空字符串，如果沒有值可以找到。

HTH