Question

我有SQLite DB，我试图在listView中显示查询的值。我按照this教程为listView创建了一个自定义适配器。还使用了this个问题作为参考。

我无法在listView上看到任何数据。

自定义listView行应该包含3个项目 - 描述，日期＆amp;金额（视图在this xml中定义）。这些值是从db中获取的。从db获取看起来很好。

我的自定义适配器代码：

public class TransactionListAdapter extends BaseAdapter {
    Context context;
    ArrayList<TransactionItem> transactionList; 
    // Code for TransactionItem class : https://gist.github.com/bharatkrishna/5175105

    public TransactionListAdapter(Context context, ArrayList<TransactionItem> list) {

        this.context = context;
        transactionList = list;
    }

    @Override
    public int getCount() {
        return transactionList.size();
    }

    @Override
    public Object getItem(int position) {
        return transactionList.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Log.d("adpater", "I am in adapter"); // Doesn't seem to get to this point as I don't see the log message
        View element;
        TransactionItem transactionItem = transactionList.get(position);        
        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            element = inflater.inflate(R.layout.row_entry, null);

         } else {
             element = convertView;
         }
        // Code of XML file with these widgets defined: https://gist.github.com/bharatkrishna/5175158
        TextView descTextView = (TextView) convertView.findViewById(R.id.descText_Report);
        descTextView.setText(transactionItem.getDescription());

        TextView dateTextView = (TextView) convertView.findViewById(R.id.dateText_Report);
        dateTextView.setText(transactionItem.getDate());

        TextView amountTextView = (TextView) convertView.findViewById(R.id.amountText_Report);
        amountTextView.setText(Float.toString(transactionItem.getAmount()));        

        return convertView;
    }

}

我在我的活动中使用此适配器如下：

public class ReportsActivity extends Activity {
ListView listView;  
private DatabaseHelper db;
private Cursor transactions;
...
...
private void showList() {
    ArrayList<TransactionItem> transactionList = new ArrayList<TransactionItem>();
    db = new DatabaseHelper(this);          
    transactions = db.getTransaction();

    // This successfully dumps the db contents to log output. Querying from DB seems to be working fine.    
    Log.d("db", DatabaseUtils.dumpCursorToString(transactions)); 

        if (transactions != null && transactions.getCount() != 0) {
            do {
                TransactionItem transactionItem = new TransactionItem();

                transactionItem.setDescription(transactions.getString(transactions.getColumnIndex("description")));

                transactionItem.setDate(transactions.getString(transactions.getColumnIndex("date")));

                transactionItem.setAmount(transactions.getFloat(transactions.getColumnIndex("amount")));
            } while (transactions.moveToNext());
    }           
        TransactionListAdapter transactionListAdapter = new TransactionListAdapter(ReportsActivity.this, transactionList);
        listView.setAdapter(transactionListAdapter); //listView is defined in onCreate() method
  }
}

我哪里错了。

感谢。

编辑：更改了TransactionListAdapter的getView（）方法的代码，摆脱了其他情况。我正在改变代码和在这里粘贴了一个有缺陷的代码。 @James Baca发现了这一点。我现在有：

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    TransactionItem transactionListItems = transactionList.get(position);
    Log.d("adpater", "I am in adapter");
    if (convertView == null) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.row_entry, null);

    }       

    TextView descTextView = (TextView) convertView.findViewById(R.id.descText_Report);
    descTextView.setText(transactionListItems.getDescription());

    TextView dateTextView = (TextView) convertView.findViewById(R.id.dateText_Report);
    dateTextView.setText(transactionListItems.getDate());

    TextView amountTextView = (TextView) convertView.findViewById(R.id.amountText_Report);
    amountTextView.setText(Float.toString(transactionListItems.getAmount()));       

    return convertView;
}

Answer 1

试试这个

您尚未将交易对象设置为列表，因此您的列表为空

添加此

transactionList.add(transactionItem);

在showList()方法

的while循环中

Answer 2

我认为你应该将convertview替换为element .. like this

     TextView descTextView = (TextView) element.findViewById(R.id.descText_Report);
    descTextView.setText(transactionItem.getDescription());

    TextView dateTextView = (TextView) element.findViewById(R.id.dateText_Report);
    dateTextView.setText(transactionItem.getDate());

    TextView amountTextView = (TextView) element.findViewById(R.id.amountText_Report);
    amountTextView.setText(Float.toString(transactionItem.getAmount())); 

    return element;

Answer 3

当convertView为null时，你有一个convertView.findViewById（）的错误，这可能会失败。首次使用适配器并且最初没有传入convertView时会发生这种情况。

我建议：

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    Log.d("adpater", "I am in adapter"); // Doesn't seem to get to this point as I don't see the log message

    TransactionItem transactionItem = transactionList.get(position);        
    if (convertView == null) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.row_entry, null);

     } 
    // Code of XML file with these widgets defined: https://gist.github.com/bharatkrishna/5175158
    TextView descTextView = (TextView) convertView.findViewById(R.id.descText_Report);
    descTextView.setText(transactionItem.getDescription());

    TextView dateTextView = (TextView) convertView.findViewById(R.id.dateText_Report);
    dateTextView.setText(transactionItem.getDate());

    TextView amountTextView = (TextView) convertView.findViewById(R.id.amountText_Report);
    amountTextView.setText(Float.toString(transactionItem.getAmount()));        

    return convertView;
}

ListView使用自定义适配器不显示任何内容

3 个答案: