Question

现在我正在尝试使用

打开数据库

db=SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.OPEN_READONLY);
        Cursor resultset = db.query("person_table", null, null, null, null, null, null);

所以我使用Cursor来获取db查询返回的每个结果集。每个结果集返回我添加到数组中以在ListView中查看。下面是我从db

获取数据的代码

package com.android.my.mypackage;

import android.app.ListActivity;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.Cursor;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.List;

public class personDetail extends ListActivity{

    private static String DBPATH="data/data/com.android.my.mypackage/databases/";
    private static String DBNAME="persondb.db";
    private View refView;
    public ListView personlist;

    public personDetail(View v, ListView l){
        refView = v;
        personlist = l;
    }

    public void DisplayPersonDetail(){
        SQLiteDatabase db=null;
        String path=DBPATH+DBNAME;

        db=SQLiteDatabase.openDatabase(path, null, SQLiteDatabase.OPEN_READONLY);
        Cursor resultset = db.query("person_table", null, null, null, null, null, null);
        if(resultset.getCount()==0){            
            /*please ignore this block*/
        }else{
            resultset.moveToFirst();
            List<String> arl = new ArrayList<String>();         
            while(resultset.isAfterLast()==false){

                arl.add(resultset.getString(6).toString() + "@@" + resultset.getString(1).toString());                              
                resultset.moveToNext();                         
            }
            //Toast.makeText(refView.getContext(), "Arl value " + arl, Toast.LENGTH_LONG).show();
            personlist.setAdapter(new PersonAdapter(this, arl));
        }       
    }

}

以下是PersonAdapter类

package com.android.my.mypackage;

import java.util.List;
import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import android.widget.ImageView;


public class PersonAdapter extends ArrayAdapter<String>{
    private static Activity context;
    private final List<String> list;

    public PersonAdapter(Activity c, List<String> list){
        super(context, R.layout.person_adapter, list);
        this.context = c;
        this.list = list;
    }

    static class ViewHolder{
        private TextView descHolder;
        private ImageView typeHolder;
    }

    public View getView(int position, View convertview, ViewGroup group){

        ViewHolder holder;
        View lView = convertview;

        if(lView==null){
            LayoutInflater inf = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            lView = inf.inflate(R.layout.person_adapter, group, true);
            holder = new ViewHolder();
            holder.descHolder = (TextView) lView.findViewById(R.id.personDescLbl);
            holder.typeHolder = (ImageView) lView.findViewById(R.id.personCategoryImage);
        }else{
            holder = (ViewHolder) lView.getTag();
        }

        holder.descHolder.setText(list.get(position).toString().split("@@")[0]);
        String category = list.get(position).toString().split("@@")[1];
        if(category.equals("Male")){
            holder.typeHolder.setImageResource(R.drawable.male);
        }else{
            holder.typeHolder.setImageResource(R.drawable.female);
        }               
        return lView;
    }
}

和我的person_adapter布局用列表视图充气

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
    <TextView 
        android:id="@+id/personDescLbl"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:gravity="center_vertical"/>
    <ImageView 
        android:id="@+id/personCategoryImage"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"/>       
</LinearLayout>

我的代码基于此site的教程。但我在PersonAdapter类中得到Nullpointer异常错误，该错误指向

super(context, R.layout.person_adapter, list);

在此之前，我使用表格布局显示结果集，并且它正在工作查找。但是，使用表格布局来显示大量数据并不是一个很好的实用方法，因为它可以节省时间和内存。所以请帮我完成listView适配器。感谢。

Answer 1

在您的PersonAdapter中，当您致电context构造函数时，您的null字段为super。您只在第二行初始化它。您应该将活动作为super的第一个参数（您称之为c），然后影响您的context字段。

public class PersonAdapter extends ArrayAdapter<String>{
    private static Activity context;
    ...

    public PersonAdapter(Activity c, List<String> list){
        super(c, R.layout.person_adapter, list);
        this.context = c;
        this.list = list;
   }

Android：具有textview和image的ListView元素，基于数据库查询结果的结果

1 个答案: