數組列表 <HashMap<String,String> &gt;獲得價值

Question

幫助從ArrayList獲取值

data = new ArrayList<Map<String, String>>();
for (int i = 0; i < marks.length; i++) {
    HashMap<String, String> m = new HashMap<String, String>();
    m.put("title", marks[i].getUserName());
    m.put("mark", marks[i].getMark().toString());
    m.put("type", marks[i].getType().toString());
    m.put("description", marks[i].getDescription());
    data.add(m);
}

嘗試從適配器中取出一個ArrayList並將值寫入數組：

data = simpleAdapter.getData();
MarksRead[] marksReads = new MarksRead[data.size()];
for (int i = 0; i < data.size(); i++) {
    marksReads[i].setDescription(data(i).get("description"));
    marksReads[i].setMark(Integer.valueOf(data.get(i).get("mark")));
    marksReads[i].setType(Integer.valueOf(data.get(i).get("type")));
}

在線marksReads[i].setDescription(data(i).get("description")); 輸出為Exception NullPointerException.

幫助，正確的做法。

Answer 1

您必須先創建對象才能使用它

for (int i = 0; i < data.size(); i++) {
    marksReads[i] = new MarksReads();
    marksReads[i].setDescription(data(i).get("description"));
    marksReads[i].setMark(Integer.valueOf(data.get(i).get("mark")));
    marksReads[i].setType(Integer.valueOf(data.get(i).get("type")));
 }