通過Android中的getItemAtPosition方法獲取id

Question

我想在點擊項目後從數據庫中獲取項目的id，然後我想將此id發送到其他活動。

我得到一個錯誤：

java.lang.ClassCastException: java.lang.String cannot be cast to com.example.myPackage.Place 

該錯誤是由線造成：

Place mPlace = (Place)(lv.getItemAtPosition(position)); 

當然，如果我改變下面的行線，應用程序工作，但我越來越在屏幕上顯示單行的名稱，而不是id。

String str = (String)(lv.getItemAtPosition(position)); 

這是我的完整代碼。

public class VisitedPlaces extends ListActivity { 

    private ArrayList<String> results = new ArrayList<String>(); 

    protected void onCreate(Bundle savedInstanceState) { 
     . 
     . 
     . 
     fillTheList(); 
     displayResultList(); 
    } 

    public void fillTheList(){ 
     DataBaseHelper dbHelper = new DataBaseHelper(this.getApplicationContext()); 

     List<Place> placesList = new ArrayList<>(); 
     String sql = "SELECT _id, Name, Description, Latidute, Longtidute FROM Places WHERE Visited=1"; 
     placesList = dbHelper.getAllPlaces(sql); 

     for (Place place : placesList){ 
      results.add(place.getPlaceName()); 
     } 
    } 

    public void displayResultList() { 

     ListView lv = getListView(); 
     lv.addHeaderView(tvNew); 
     lv.setTextFilterEnabled(true); 
     setListAdapter(new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, results)); 

     lv.setOnItemClickListener(new OnItemClickListener() { 
      @Override 
      public void onItemClick(AdapterView<?> parent, View view, int position, 
        long id) { 

//  String str = (String)(lv.getItemAtPosition(position)); 
     Place mPlace = (Place)(lv.getItemAtPosition(position)); //HERE IS A PROBLEM 
     int mID = mPlace.getID(); 

     Toast.makeText(getApplicationContext(),"Click ListItem: " + mID + ", " + id + ", " , Toast.LENGTH_LONG).show();        

     goToPlaceDescriptions(view, id); 

      } 
     });  
    } 

    public void goToPlaceDescriptions(View v, long id) { 
     Intent intent = new Intent(this, PlaceDescriptions.class); 
     intent.putExtra("id", id); 
     startActivity(intent); 
    } 
} 

can somebode help me？

Answer 1

的問題是，你使用ArrayAdapter。我認爲你的自定義適配器將從BaseAdapter擴展將是更好的解決方案。

請看看下面的代碼：

自定義適配器類：

 public class PlaceListAdapter extends BaseAdapter { 

     private List<Place> mPlaceList; 
     private Context mContext; 

     PlaceListAdapter(List<Place> placeList, Context c){ 
      mPlaceList = new LinkedList<>(placeList); 
      mContext = c; 
     } 
     @Override 
     public int getCount() { 
      return mPlaceList.size(); 
     } 

     @Override 
     public Place getItem(int i) { 
      return mPlaceList.get(i); 
     } 

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

     @Override 
     public View getView(int i, View view, ViewGroup viewGroup) { 
      //here inflate and return some view it can be text view 
     } 
    } 

現在你的代碼將看起來像下面

 public class VisitedPlaces extends ListActivity { 

     private List<Place> results = new ArrayList<Place>(); 

     protected void onCreate(Bundle savedInstanceState) { 
      . 
      . 
      . 
      fillTheList(); 
      displayResultList(); 
     } 

     public void fillTheList(){ 
      DataBaseHelper dbHelper = new DataBaseHelper(this.getApplicationContext()); 
      String sql = "SELECT _id, Name, Description, Latidute, Longtidute FROM Places WHERE Visited=1"; 
      List<Place> placesList = dbHelper.getAllPlaces(sql); 

      for (Place place : placesList){ 
       results.add(place); 
      } 
     } 

     public void displayResultList() { 

      ListView lv = getListView(); 
      lv.addHeaderView(tvNew); 
      lv.setTextFilterEnabled(true); 
      setListAdapter(new PlaceListAdapter(results, this)); 

      lv.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
       @Override 
       public void onItemClick(AdapterView<?> parent, View view, int position, 
             long id) { 
        Place mPlace = (((PlaceListAdapter)parent.getAdapter()).getItem(position)); //HERE IS A PROBLEM 
        int mID = mPlace.getID(); 

        Toast.makeText(getApplicationContext(),"Click ListItem: " + mID + ", " + id + ", " , Toast.LENGTH_LONG).show(); 

        goToPlaceDescriptions(view, id); 

       } 
      }); 
     } 

     public void goToPlaceDescriptions(View v, long id) { 
      Intent intent = new Intent(this, PlaceDescriptions.class); 
      intent.putExtra("id", id); 
      startActivity(intent); 
     } 

    } 

我可以在代碼中做出了一些錯誤，但想法是最重要的。 請閱讀有關定製列表適配器。

Answer 2

沒有鑄造，這樣做：

設置placesList爲全局變量，那麼此線以獲得正確的Place：

Place mPlace=placesList.get(position);