java - tableList 哪里变成 null 了？为什么？

Question

我正在实现一个适配器来获取 List 和 Hashmap 并将它们分别转换为可扩展 ListView 的标题和子项。在构造函数的 Log 语句中，显示值已成功传输到本地列表。但随后它突然变成空。

我无法确定哪里出了问题。请帮忙。

这是我的适配器类的代码:

class ExpandableListViewAdapterDemo extends BaseExpandableListAdapter{

Context context = null;
private List<String> headersList;//semester's name and year
private HashMap<String, List<String>> tableList;//course names with its grades and gpa

static final String TAG = "**Adapter Demo**";

ExpandableListViewAdapterDemo(Context context, List<String> list,
                              HashMap<String, List<String>> hashMap){
    this.context = context;
    headersList = list;
    tableList = hashMap;
    Log.e(TAG, "hashmap list value = "+hashMap.get("Spring 2016"));
    Log.e(TAG, "initial table list value = "+tableList.get("Spring 2016"));
    printMap(tableList);
    //printAll();
    Log.e(TAG, "groupCount = "+getGroupCount());

}

void printAll(){
    Log.e(TAG, "headers count = "+headersList.size());
    for (int i = 0; i < headersList.size() ; i++) {
        Log.e(TAG, "header at i="+i+" ,"+headersList.get(i));
    }
    printMap(tableList);
}

private static void printMap(HashMap mp) {
    Iterator it = mp.entrySet().iterator();
    while (it.hasNext()) {
        HashMap.Entry pair = (HashMap.Entry)it.next();
        Log.e(TAG, "#253 : "+pair.getKey() + " = " + pair.getValue());
        it.remove(); // avoids a ConcurrentModificationException
    }
}

@Override
public int getGroupCount() {
    Log.e(TAG, "#299 : table list value = "+tableList.get("Spring 2016"));
    return headersList.size();
}

@Override
public int getChildrenCount(int i) {
    //Log.e(TAG, "at i="+i+" "+headersList.get(i));
    int returns = 0;
    Log.e(TAG, "#307 : table list value = "+tableList.get("Spring 2016"));
    if (tableList.get(headersList.get(i)) != null)
        returns = tableList.get(headersList.get(i)).size();
    else
        Log.e(TAG, "tableList is null");
    Log.e(TAG, "details size = "+returns);
    Log.e(TAG, "group count = "+getGroupCount());
    int tosubtract = 2 * getGroupCount();
    if (returns>tosubtract)
        returns = returns - tosubtract - 2;
    Log.e(TAG, "child count returns = "+String.valueOf(returns) );
    return i;
}

@Override
public Object getGroup(int i) {
    Log.e(TAG, "#323 : table list value = "+tableList.get("Spring 2016"));
    return headersList.get(i);
}

@Override
public Object getChild(int i, int i1) {
    Log.e(TAG, "#329 : table list value = "+tableList.get("Spring 2016"));
    return tableList.get(headersList.get(i)).get(i1);
}

@Override
public long getGroupId(int i) {
    Log.e(TAG, "#335 : table list value = "+tableList.get("Spring 2016"));
    return i;
}

@Override
public long getChildId(int i, int i1) {
    Log.e(TAG, "#340 : table list value = "+tableList.get("Spring 2016"));
    return i1;
}

@Override
public boolean hasStableIds() {
    Log.e(TAG, "#347 : table list value = "+tableList.get("Spring 2016"));
    return false;
}

@Override
public View getGroupView(int i, boolean b, View view, ViewGroup viewGroup) {
    Log.e(TAG, "#353 : table list value = "+tableList.get("Spring 2016"));
    String semesterTitle = (String) getGroup(i);
    if (view == null){
        LayoutInflater inf = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = inf.inflate(R.layout.previous_semesters_result_list_headers, null);
    }

    TextView semesterName = (TextView) view.findViewById(R.id.semester_name);
    semesterName.setText(semesterTitle);
    return view;
}

@Override
public View getChildView(int i, int i1, boolean b, View view, ViewGroup viewGroup) {
    Log.e(TAG, "#367 : table list value = "+tableList.get("Spring 2016"));
    String courseIdTitle = (String) getChild(i, i1);
    String gpa = (String) getChild(i, i1+getChildrenCount(i));//previously i1+4
    String grade = (String) getChild(i, i1+getChildrenCount(i)+getChildrenCount(i));
    if (view == null){
        LayoutInflater inf = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = inf.inflate(R.layout.previous_semesters_results_list_child, null);
    }
    TextView courseIdValue = (TextView) view.findViewById(R.id.course_id_column_value);
    courseIdValue.setText(courseIdTitle);
    TextView gradeValue = (TextView) view.findViewById(R.id.grade_column_value);
    gradeValue.setText(grade);
    TextView gpaValue = (TextView) view.findViewById(R.id.gpa_column_value);
    gpaValue.setText(gpa);
    return view;
}

@Override
public boolean isChildSelectable(int i, int i1) {
    Log.e(TAG, "#386 : table list value = "+tableList.get("Spring 2016"));
    return true;
}
}

这是我的日志:

Answer 1

您在打印 map 时删除了该项目，

it.remove(); // avoids a ConcurrentModificationException

只要删除它就可以正常工作。

private static void printMap(HashMap mp) {
    Iterator it = mp.entrySet().iterator();
    while (it.hasNext()) {
        HashMap.Entry pair = (HashMap.Entry)it.next();
        Log.e(TAG, "#253 : "+pair.getKey() + " = " + pair.getValue());
        //it.remove(); // avoids a ConcurrentModificationException
    }
}