如何通過映射值到適配器

Question

我有這個適配器

public class BookcaseAdapter extends SectionableAdapter implements 
     View.OnClickListener { 

    private Activity activity; 
    private Map<String, List<Sponsor>> mSponsorMap; 

    public BookcaseAdapter(Activity activity, LayoutInflater inflater, 
      int rowLayoutID, int headerID, int itemHolderID, int resizeMode, Map<String, List<Sponsor>> sponsorMap) { 
     super(inflater, rowLayoutID, headerID, itemHolderID, resizeMode); 
     this.activity = activity; 
     mSponsorMap = sponsorMap; 
    } 

    @Override 
    public Object getItem(int position) { 
     for (int i = 0; i < mSponsorMap.size(); ++i) { 
      if (position < mSponsorMap.get(i).size()) { 
       return mSponsorMap.get(i).get(position); 
      } 
      position -= mSponsorMap.get(i).size(); 
     } 
     // This will never happen. 
     return null; 
    } 

    @Override 
    protected int getDataCount() { 
     int total = 0; 
     for (int i = 0; i < mSponsorMap.size(); ++i) { 
      total += mSponsorMap.get(i).size(); 
     } 
     return total; 
    } 

    @Override 
    protected int getSectionsCount() { 
     return mSponsorMap.size(); 
    } 


    @Override 
    protected int getCountInSection(int index) { 
     return mSponsorMap.get(index).size(); 
    } 

    @Override 
    protected int getTypeFor(int position) { 
     int runningTotal = 0; 
     int i = 0; 
     for (i = 0; i < mSponsorMap.size(); ++i) { 
      int sectionCount = mSponsorMap.get(i).size(); 
      if (position < runningTotal + sectionCount) 
       return i; 
      runningTotal += sectionCount; 
     } 
     // This will never happen. 
     return -1; 
    } 

    @Override 
    protected String getHeaderForSection(int section) { 
     List<List<Sponsor>> l = new ArrayList<List<Sponsor>>(mSponsorMap.values()); 
     String string = l.get(section).get(0).getCountry_name(); 
     return string; 
    } 

    @Override 
    protected void bindView(View convertView, int position) { 
     String title = (String) getItem(position); 
     ImageView label = (ImageView) convertView 
       .findViewById(R.id.bookItem_title); 
     label.setImageResource(R.drawable.place_holder_thumb); 
     convertView.setOnClickListener(this); 
    } 

    @Override 
    public void onClick(View v) { 
     Intent i = new Intent(Intent.ACTION_SEARCH); 
     ImageView label = (ImageView) v.findViewById(R.id.bookItem_title); 
//  String text = label.getText().toString(); 
//  i.putExtra(SearchManager.QUERY, text); 

//  activity.startActivity(i); 
     label.setImageResource(R.drawable.place_holder_thumb); 
    } 

} 

當從我的活動我把這種適配器，並傳遞給sponsorMap重視它越來越空，我有空指針exceptoin。

我調試它發現，當我打電話適配器和它達到super(inflater, rowLayoutID, headerID, itemHolderID, resizeMode);，之後叫

@Override 
    protected int getSectionsCount() { 
     return mSponsorMap.size(); 
    } 

我'確保mSponsorMap = sponsormap還沒有被調用。爲什麼發生這種情況？

Answer 1

它會被調用，但後來，超級構造函數被調用時得到的異常阻止了實際到達的構造函數代碼。

就在您的覆蓋方法添加的NPE後衛：

@Override 
protected int getSectionsCount() { 
    return mSponsorMap == null ? 0 : mSponsorMap.size(); 
} 

另外，您也可以初始化mSponsorMap到一個空的地圖：

private Map<String, List<Sponsor>> mSponsorMap = Collections.emptyMap(); 

然後在你的構造做：

mSponsorMap.putAll(sponsorMap); 

乾杯，