如何解决getChidrenCount 空指针，我得到了一个冗余列表
我想在来自 sqlite 数据库的 ExpandableList 中按类别显示文章列表。组是类别，项目是文章。 我在文章中的作用
public List<Article> getAllArticle() {
List<Article> listArticle = new ArrayList<Article>();
Article art = null;
String[]columns = {DBHelper.COLUMN_ARTICLES_NAME,DBHelper.COLUMN_ARTICLES_PRIX,DBHelper.COLUMN_ARTICLES_DATE};
mDatabase = new DBHelper(mContext).getWritableDatabase();
Cursor c = mDatabase.query(DBHelper.TABLE_ARTICLES,columns,null,null);
c.movetoFirst();
while (!c.isAfterLast()) {
art = new Article();
art.setName(c.getString(c.getColumnIndex(DBHelper.COLUMN_ARTICLES_NAME)));
art.setPrix(c.getDouble(c.getColumnIndex(DBHelper.COLUMN_ARTICLES_PRIX)));
art.setDateAchat(c.getString(c.getColumnIndex(DBHelper.COLUMN_ARTICLES_DATE)));
listArticle.add(art);
c.movetoNext();
}
public List<Article> getArticleByCategory(int catId) {
List<Article> listArticle = new ArrayList<Article>();
Article art = null;
String[]columns = {DBHelper.COLUMN_ARTICLES_NAME,DBHelper.COLUMN_ARTICLES_DATE};
String selection = DBHelper.COLUMN_ARTICLES_CATEGORY + " = ? ";
String[] selectionArgs = new String[]{String.valueOf(catId)};
mDatabase = new DBHelper(mContext).getWritableDatabase();
Cursor c = mDatabase.query(DBHelper.TABLE_ARTICLES,selection,selectionArgs,null);
c.movetoFirst();
while (!c.isAfterLast()) {
art = new Article();
art.setName(c.getString(c.getColumnIndex(DBHelper.COLUMN_ARTICLES_NAME)));
art.setPrix(c.getDouble(c.getColumnIndex(DBHelper.COLUMN_ARTICLES_PRIX)));
art.setDateAchat(c.getString(c.getColumnIndex(DBHelper.COLUMN_ARTICLES_DATE)));
listArticle.add(art);
c.movetoNext();
}
我的活动
ExpandableListView listArt; ArrayList listGroup = new ArrayList();
HashMap
BottomNavigationView bnav;
NavigationView nav;
Context ctx;
ArrayList<Integer> lva;
private ListArticles mAdapter;
DBHelper helper = new DBHelper(this);
ArticleDAO DB = new ArticleDAO(this);
CategoryDAO CA = new CategoryDAO(this);
Button shop;
CheckBox sh;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
nomUser = (TextView) findViewById(R.id.loguse);
identi = (TextView) findViewById(R.id.numUse);
listArt = (ExpandableListView) findViewById(R.id.listArticle);
emptyArt = (TextView) findViewById(R.id.link_to_shopplist);
cat = (TextView) findViewById(R.id.link_to_cat);
Ajt = (TextView) findViewById(R.id.link_to_ajout);
shop = (Button) findViewById(R.id.btn_send);
Intent in = getIntent();
Bundle b = in.getExtras();
if (b != null) {
String j = b.getString("username");
nomUser.setText("" + j);
int k = (int) b.get("ID");
identi.setText("" + k);
}
int ids = Integer.parseInt(identi.getText().toString());
long iduse = Long.valueOf(ids);
Ajt.setonClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(),AjoutArticleActivity.class);
i.putExtra("id",ids);
startActivity(i);
}
});
shop.setonClickListener(new View.OnClickListener() {
public void onClick(View v) {
ArrayList<String> mylist = new ArrayList<String>();
for (int i = 0; i < listArt.getChildCount(); i++) {
sh = (CheckBox) listArt.getChildAt(i).findViewById(R.id.check_art);
if (sh instanceof CheckBox) {
CheckBox check = (CheckBox) sh;
if (check.isChecked()) {
//na = listChild.get("name").get(i).getName();
na = listChild.get("name").get(i);
mylist.add(na);
Log.d("h","the list is " + mylist);
}
}
}
inte = new Intent(getApplicationContext(),ShoppingListActivity.class);
inte.putExtra("val",mylist);
inte.putExtra("is",iduse);
startActivity(inte);
}
});
ArrayList<Integer> arrayList = new ArrayList<>();
List<Category> mListCategory = CA.getAllCategory();
int is;
for (int K = 0; K <= mListCategory.size() - 1; K++) {
String nom = mListCategory.get(K).getName();
is = (int) mListCategory.get(K).getId();
arrayList.add(is);
listGroup.add(nom);
Log.d("h","the cat is " + arrayList);
}
ArrayList<String> arti = new ArrayList<>();
List<Article> la = null;
for (Integer str : arrayList) {
la = DB.getArticleByCategory(str);
for (int i = 0; i < la.size(); i++) {
String no = la.get(i).getName();
arti.add(no);
}
listChild.put(str,arti);
}
mAdapter = new ListArticles(listGroup,listChild);
listArt.setAdapter(mAdapter);
}
我的领养者
public class ListArticles extends Baseexpandablelistadapter {
public static final String TAG = "ListArticles";
private List<Category> listCat;
private LayoutInflater mInflater;
private SparseBooleanArray mCheckStates;
HashMap<Category,ArrayList<String>> listChild;
public ListArticles(HashMap<Category,ArrayList<String>> listChild,List<Category> listCat) {
this.listCat=listCat;
this.listChild=listChild;
mCheckStates = new SparseBooleanArray(listChild.size());
}
public boolean isChecked(int position) {
return mCheckStates.get(position,false);
}
public void setChecked(int position,boolean isChecked) {
mCheckStates.put(position,isChecked);
}
public void toggle(int position) {
setChecked(position,!isChecked(position));
}
@Override
public void onCheckedChanged(CompoundButton buttonView,boolean isChecked) {
mCheckStates.put((Integer) buttonView.getTag(),isChecked);
}
@Override
public int getGroupCount() {
return listCat.size();
}
@Override
public int getChildrenCount(int i) {
return listChild.get(listCat.get(i)).size();
}
@Override
public Object getGroup(int i) {
return listCat.get(i);
}
@Override
public Object getChild(int i,int i1) {
return listChild.get(listCat.get(i)).get(i1);
}
@Override
public long getGroupId(int groupPosition) {
return 0;
}
@Override
public long getChildId(int groupPosition,int childPosition) {
return 0;
}
@Override
public boolean hasstableIds() {
return false;
}
@Override
public View getGroupView(int i,boolean v,View view,ViewGroup viewGroup) {
view = LayoutInflater.from(viewGroup.getContext())
.inflate(android.R.layout.simple_expandable_list_item_1,viewGroup,false);
TextView textView=(TextView) view.findViewById(android.R.id.text1);
String sGroup = String.valueOf(getGroup(i));
textView.setText(sGroup);
textView.setTypeface(null,Typeface.BOLD);
textView.setTextColor(Color.BLUE);
return view;
}
@Override
public View getChildView(int i,int i1,boolean b,ViewGroup viewGroup) {
view = LayoutInflater.from(viewGroup.getContext())
.inflate(R.layout.list_item_article,false);
TextView txtArticleName = (TextView) view.findViewById(R.id.txt_article_name);
TextView txtPrix = (TextView) view.findViewById(R.id.txt_prix);
TextView txtDate = (TextView) view.findViewById(R.id.txt_date);
CheckBox chekArt=(CheckBox) view.findViewById(R.id.check_art);
List<Article> currentItem = (List<Article>) getChild(i,i1);
// String sChild = String.valueOf(getChild(i,i1));
//txtArticleName.setText(sChild);
if(currentItem != null) {
String name = String.valueOf(currentItem.get(0));
txtArticleName.setText(name);
String prix = String.valueOf(currentItem.get(1));
txtPrix.setText(prix);
String date = String.valueOf(currentItem.get(2));
txtDate.setText(date);
chekArt.setTag(i,i1);
chekArt.setChecked(mCheckStates.get(i,false));
chekArt.setonCheckedchangelistener(this);
}
return view;
}
@Override
public boolean isChildSelectable(int groupPosition,int childPosition) {
return false;
}
class ViewHolder {
TextView txtArticleName;
TextView txtPrix;
TextView txtDate;
CheckBox chekArt;
}
我得到了 java.lang.classCastException：java.util.ArrayList 无法转换为 java.util.HashMap 进程：com.example.gestcourses，PID：22664
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