android - 无法将 ArrayList 绑定(bind)到适配器

Question

我是 Android 的初学者。我想在我的 ListView 上方添加一个搜索组件，所以我遵循这个 example

不幸的是，我在这一行得到了 JavaNullpointer:

   lv1.setAdapter(adapter);

但是当我调试它时，我的数组列表已满。

// Pass results to ListViewAdapter Class
        arraylist = (ArrayList<Client_Pers>) dbcon.ReadData();
        adapter = new CustomListAdapter(this, arraylist);

这是我的主类:

public class MainActivity extends Activity {

    ArrayList<Client_Pers> arraylist = new ArrayList<Client_Pers>();
    CustomListAdapter adapter;
    SQLController   dbcon;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); 

        final ListView lv1 = (ListView) findViewById(R.id.theclient);
        final EditText inputSearch = (EditText)findViewById(R.id.editText_Search);

        dbcon = new SQLController(this);
        dbcon.open();

        dbcon.insertSomeItmes(); 

        // Pass results to ListViewAdapter Class
        arraylist = (ArrayList<Client_Pers>) dbcon.ReadData();
        adapter = new CustomListAdapter(this, arraylist);

        // Binds the Adapter to the ListView
        lv1.setAdapter(adapter);



        /**
         * Enabling Search Filter
         * */
        inputSearch.addTextChangedListener(new TextWatcher() {

            @Override
            public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
                // When user changed the Text
                 String text = inputSearch.getText().toString().toLowerCase(Locale.getDefault());
                 adapter.filter(text);
            }

            @Override
            public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,
                    int arg3) {
                // TODO Auto-generated method stub

            }

            @Override
            public void afterTextChanged(Editable arg0) {
                // TODO Auto-generated method stub                          
            }
        });

        dbcon.close();

    }

....

我的 Controller 类:

public class SQLController {

    private DBHelper dbhelper;
    private Context ourcontext;
    private SQLiteDatabase database;
    private ArrayList<Client_Pers> results = new ArrayList<Client_Pers>();

    public SQLController(Context c) {
        ourcontext = c;
    }

    public SQLController open() throws SQLException {
        dbhelper = new DBHelper(ourcontext);
        database = dbhelper.getWritableDatabase();
        return this;
    }

    public void close() {
        dbhelper.close();
    }

    public ArrayList<Client_Pers> ReadData() {
            try {               

                String SQL_syntax = "SELECT * FROM " +  DBHelper.tableName;
//              if (FilterName != null && !FilterName.isEmpty())
//              {SQL_syntax = "SELECT * FROM " + DBHelper.tableName + "WHERE "+ DBHelper.KEY_RsNom + "LIKE '%" + FilterName + "%'";}

                Cursor c = database.rawQuery(SQL_syntax, null);
                if (c != null ) {
                    if  (c.moveToFirst()) {
                        do {
                            Client_Pers ClientItem = new Client_Pers();

                            String LeCodeClient = c.getString(c.getColumnIndex(DBHelper.KEY_CodeClient));
                            ClientItem.setLeCodeCl(LeCodeClient);

                            String LeRsNom = c.getString(c.getColumnIndex(DBHelper.KEY_RsNom));
                            ClientItem.setLeRsNom(LeRsNom);

                            String LeVille = c.getString(c.getColumnIndex(DBHelper.KEY_Ville));
                            ClientItem.setLaVille(LeVille);

                            String LeTel = c.getString(c.getColumnIndex(DBHelper.KEY_Tel));
                            ClientItem.setLeTel(LeTel);

                            results.add(ClientItem);
                        }while (c.moveToNext());
                    } 
                }
            } catch (SQLiteException se ) { 
                Log.e(getClass().getSimpleName(), "Could not create or Open the database");
            }
            return results;
        }

    public long createItmes(String LeCodeClient, String LeRsNom, String LeVille, String LeTel) {

      ContentValues initialValues = new ContentValues();
      initialValues.put(DBHelper.KEY_CodeClient, LeCodeClient);
      initialValues.put(DBHelper.KEY_RsNom, LeRsNom);
      initialValues.put(DBHelper.KEY_Ville, LeVille);
      initialValues.put(DBHelper.KEY_Tel, LeTel);


      return database.insert(DBHelper.tableName, null, initialValues);
     }

    public void insertSomeItmes() {  
    createItmes("850007","A B S","MONTAIGU","02 51 94 18 46");
    createItmes("850012","SARL A D I P A"," SAINT HERBLAIN CEDEX","02 40 92 21 2");
    createItmes("850024","AIZENAY AUTO","AIZENAY","02 51 94 60 40");    
    createItmes("850034","AMS","OLONNE SUR MER","02 51 95 05 23");
    createItmes("850042","ETS ARMOUET","LES HERBIERS","02 51 92 98 59");
     }  
}

我的自定义列表适配器:

public class CustomListAdapter extends BaseAdapter {

    private List<Client_Pers> Client_Pers_list = null;
    private ArrayList<Client_Pers> Client_Pers_arraylist;
    private LayoutInflater layoutInflater;

    public CustomListAdapter(Context context,List<Client_Pers> Client_Pers_list) {
        this.Client_Pers_arraylist = new ArrayList<Client_Pers>();
        this.Client_Pers_arraylist.addAll(Client_Pers_list);
        layoutInflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return Client_Pers_list.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return Client_Pers_list.get(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        ViewHolder holder;
        if (convertView == null) {
            convertView = layoutInflater.inflate(R.layout.list_row_layout, null);
            holder = new ViewHolder();
            holder.CodeClView = (TextView) convertView.findViewById(R.id.CodeCL);
            holder.RsNomView = (TextView) convertView.findViewById(R.id.RsNom);
            holder.VilleView = (TextView) convertView.findViewById(R.id.LaVille);
            holder.TelView = (TextView) convertView.findViewById(R.id.TheTel);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }


        Client_Pers ClientItem = (Client_Pers)Client_Pers_arraylist.get(position);
        holder.CodeClView.setText(ClientItem.getLeCodeCl());
        holder.RsNomView.setText( ClientItem.getLeRsNom());
        holder.VilleView.setText(ClientItem.getLaVille());
        holder.TelView.setText(ClientItem.getLeTel());

        return convertView;
    }

     // Filter Class
    public void filter(String charText) {
        charText = charText.toLowerCase(Locale.getDefault());
        Client_Pers_list.clear();
        if (charText.length() == 0) {
            Client_Pers_list.addAll(Client_Pers_arraylist);
        } else {
            for (Client_Pers wp : Client_Pers_arraylist) {
                if (wp.getLeRsNom().toLowerCase(Locale.getDefault())
                        .contains(charText)) {
                    Client_Pers_list.add(wp);
                }
            }
        }
        notifyDataSetChanged();
    }

    static class ViewHolder {
        TextView CodeClView;
        TextView RsNomView;
        TextView VilleView;
        TextView TelView;
    }

}

activity_main.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.soft8.sql_test.MainActivity" >

     <EditText
         android:id="@+id/editText_Search"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_alignParentTop="true"
         android:layout_centerHorizontal="true"
         android:ems="10"
         android:hint="Chercher" />

    <ListView
        android:id="@+id/theclient"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editText_Search" >

    </ListView>


</RelativeLayout>

错误信息:

  Unable to start activity ComponentInfo{com.soft8.sql_test/com.soft8.sql_test.MainActivity}: java.lang.NullPointerException

Answer 1

你有

return Client_Pers_list.size();

在getCount()

中

这个

private List<Client_Pers> Client_Pers_list = null;

从未被初始化。

初始化为

public CustomListAdapter(Context context,List<Client_Pers> Client_Pers_list) {
    this.Client_Pers_list = Client_Pers_list;  
    this.Client_Pers_arraylist = new ArrayList<Client_Pers>();
    this.Client_Pers_arraylist.addAll(Client_Pers_list);
    layoutInflater = LayoutInflater.from(context);
}