java - Android:从ArrayList中提取数据

Question

我想从 ArrayList 中提取数据，但 LogCat 显示空值。

我的代码是:

try {
   String sql = "SELECT Cname FROM demo";
   Statement stmt = con.createStatement();
   final ResultSet rs = stmt.executeQuery(sql);
   while (rs.next()) {
      arrData.add(rs.getString("Cname").toString());
   }
   Campaign campaign_data[] = new Campaign[] {
      new Campaign(R.drawable.empty, "Today:"+ arrData.indexOf(0)),
      new Campaign(R.drawable.empty, "This Month:" + arrData.indexOf(1))
   };
} catch() {
}

Answer 1

arrData 是 ArrayList 类型吗？

您似乎正在对其调用indexOf(0)，这可能不是您想要的。

public int indexOf(Object o)

Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

我假设您打算调用 get(i)，因此请尝试以下操作:

      new Campaign(R.drawable.empty, "Today:"+ arrData.get(0)),
      new Campaign(R.drawable.empty, "This Month:" + arrData.get(1))