如何從ListView中的視圖訪問適配器對象

Question

很久以後，我回到Android，我有點卡住了一些問題。
該應用程序由佈局列表組成，每個佈局都通過適配器由模型支持。
每個佈局有幾個視圖，其中之一是一個微調。
我想在更改微調器的值時修改適配器中的數據，但我不知道如何引用適配器中的對象。

public class MainActivity extends AppCompatActivity { 
    ArrayList<Troop> values = new ArrayList<Troop>(); 
    MySimpleArrayAdapter adapter; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     values.add(new Troop()); 

     final ListView listView =(ListView) findViewById(R.id.listview); 

     adapter = new MySimpleArrayAdapter(
       this, 
       values); 
     listView.setAdapter(adapter); 
    } 

    public class Troop { 
     private String weapon; 
     private int bs; 
     private int total_modifier; 

     public Troop() { 

     } 

     public int getBs() { 
      return bs; 
     } 

     public void setBs(int bs) { 
      this.bs = bs; 
     } 
    } 

    public class MySimpleArrayAdapter extends ArrayAdapter { 
     private final Context context; 
     private ArrayList<Troop> troopers; 
     private String[] possible_bs = new String[] {"10", "11", "12", "13", "15", "16"}; 

     public MySimpleArrayAdapter(Context context, ArrayList<Troop> values) { 
      super(context, -1, values); 
      this.context = context; 
      this.troopers = values; 
     } 

     @Override 
     public View getView(int position, View convertView, ViewGroup parent) { 
       LayoutInflater inflater = (LayoutInflater) context 
         .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
       View rowView = inflater.inflate(R.layout.rowlayout, parent, false); 

       Spinner bs_spinner = rowView.findViewById(R.id.bs_spinner); 
       ArrayAdapter<String> bs_adapter = new ArrayAdapter<String>(
         context, 
         android.R.layout.simple_spinner_dropdown_item, 
         possible_bs); 
       bs_spinner.setOnItemSelectedListener(new CustomOnItemSelectedListener()); 
       bs_spinner.setAdapter(bs_adapter); 
      return rowView; 
     } 

    } 

    public class CustomOnItemSelectedListener implements AdapterView.OnItemSelectedListener { 

     public void onItemSelected(AdapterView<?> parent, View view, int pos,long id) { 
     // I want to call getBs on the Trooper correspoding to this view here 
     } 

     @Override 
     public void onNothingSelected(AdapterView<?> arg0) { 
      // TODO Auto-generated method stub 
     } 

    } 
} 

Answer 1

這裏有很多我會談到的。首先，我們來談談你的ArrayAdapter子類。

正如您對問題的評論中所述，您應該將其更改爲extends ArrayAdapter<Troop>。這將導致getItem()返回Troop而不是Object。

您不需要存儲您自己的context或troopers字段。基本的ArrayAdapter實現在mContext字段中存儲了一個上下文，您可以通過getContext()訪問它。此外，它將備份數據存儲在mObjects字段中，您可以通過getItem()訪問它。

最後，如果適配器中的所有項目要共享相同的possible_bs值，則應該將其設置爲常量。

接下來讓我們來談談AdapterView.OnItemSelectedListener。

您需要一種方法來知道哪些位置（從MySimpleArrayAdapter）您Spinner住在（相對於該項目的位置內的Spinner用戶選擇）。我建議將這個位置傳遞給構造函數，並將其保存爲私有的最終字段。

要獲取從Spinner內的適配器，您可以訪問Adapter通過調用parent.getAdapter()來頭AdapterView參數，然後將其投射到您想要的類型。

總之，你留下了這一點：

public static class MySimpleArrayAdapter extends ArrayAdapter { 

    private static final String[] POSSIBLE_BS = new String[] {"10", "11", "12", "13", "15", "16"}; 

    public MySimpleArrayAdapter(Context context, ArrayList<Troop> values) { 
     super(context, -1, values); 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
     LayoutInflater inflater = (LayoutInflater) getContext() 
       .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     View rowView = inflater.inflate(R.layout.rowlayout, parent, false); 

     Spinner bs_spinner = rowView.findViewById(R.id.bs_spinner); 
     ArrayAdapter<String> bs_adapter = new ArrayAdapter<>(
       getContext(), 
       android.R.layout.simple_spinner_dropdown_item, 
       POSSIBLE_BS); 
     bs_spinner.setOnItemSelectedListener(new CustomOnItemSelectedListener(position)); 
     bs_spinner.setAdapter(bs_adapter); 
     return rowView; 
    } 

} 

private static class CustomOnItemSelectedListener implements AdapterView.OnItemSelectedListener { 

    private final int troopPosition; 

    private CustomOnItemSelectedListener(int troopPosition) { 
     this.troopPosition = troopPosition; 
    } 

    @Override 
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) { 
     MySimpleArrayAdapter adapter = (MySimpleArrayAdapter) parent.getAdapter(); 
     int bs = adapter.getItem(troopPosition).getBs(); 
    } 

    @Override 
    public void onNothingSelected(AdapterView<?> parent) { 

    } 
} 

Answer 2

您可以在匿名類移動。

如果您想要當前的ListView元素以及內部適配器位置，您希望獲得兩個位置元素。

有可能是更清潔的方式來做到這一點，但它是第一個想法我有

public class MySimpleArrayAdapter extends ArrayAdapter<Troop> { 
    private final Context context; 
    private ArrayList<Troop> troopers; 
    private String[] possible_bs = new String[] {"10", "11", "12", "13", "15", "16"}; 

    @Override 
    public View getView(final int position, View convertView, ViewGroup parent) { 
      LayoutInflater inflater = (LayoutInflater) context 
        .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
      View rowView = inflater.inflate(R.layout.rowlayout, parent, false); 
      Spinner bs_spinner = rowView.findViewById(R.id.bs_spinner); 

      final ArrayAdapter<String> bs_adapter = new ArrayAdapter<String>(
        context, 
        android.R.layout.simple_spinner_dropdown_item, 
        possible_bs); 
      bs_spinner.setAdapter(bs_adapter); 

      bs_spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() { 

       @Override 
       public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) { 
        // You can access MySimpleArrayAdapter.this or bs_adapter 
        Troop t = troopers.get(position); // or getItem(position); 
        String bs = possible_bs[pos]; 
       } 

       @Override 
       public void onNothingSelected(AdapterView<?> arg0) { 
        // TODO Auto-generated method stub 
       } 

      }); 

     return rowView; 
    }