Question

我创建了以下名为联系人数据的类：

public class ContactData {
    String contact_id;
    String first_name;
    String last_name;
    String email;
    Uri icon;


   public ContactData(String contact_id,String first_name,String last_name,String email){
        this.contact_id=contact_id;
        this.first_name=first_name;
        this.last_name=last_name;
        this.email=email;
        this.icon= Uri.withAppendedPath(ContactsContract.Contacts.CONTENT_URI,contact_id);

       if (this.icon == null){
           this.icon = Uri.parse("android.resource://com.project.iandwe/drawable/ic_contacts");
       }
    }

    public String getContact_id() {
        return contact_id;
    }

    public void setContact_id(String contact_id) {
        this.contact_id = contact_id;
    }

    public String getFirst_name() {
        return first_name;
    }

    public void setFirst_name(String first_name) {
        this.first_name = first_name;
    }

    public String getLast_name() {
        return last_name;
    }

    public void setLast_name(String last_name) {
        this.last_name = last_name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Uri getIcon() {

        if (this.icon == null){
            this.icon = Uri.parse("android.resource://com.project.iandwe/drawable/ic_contacts");
        }

        return this.icon;
    }

    public void setIcon(Uri icon) {
        this.icon = icon;
    }



}

现在我尝试像这样创建这个类的对象：

package com.project.iandwe.Adaptor;

import android.content.Context;
import android.content.res.Resources;
import android.database.Cursor;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.CheckBox;
import android.widget.ImageView;
import android.widget.TextView;
import com.project.iandwe.Data.ContactData;
import com.project.iandwe.R;

import java.util.ArrayList;

/**
 * Created by NathanDrake on 6/4/2014.
 */

public class ContactSelectAdaptor extends BaseAdapter {

    ArrayList<ContactData> listViewRows;
    Context context;

 public ContactSelectAdaptor(Context context){

        //Resources resources = context.getResources();
        this.context =context;
        UserDatabaseAdapter userDatabaseAdapter = new UserDatabaseAdapter(context);
        Cursor cursor = userDatabaseAdapter.getUserContacts();

        while (cursor.moveToNext()){
         //   ContactData listViewRow = new ListViewRow();
             String contact_id = cursor.getString(0);
            String first_name = cursor.getString(1);
          String last_name = cursor.getString(2);
            String email = cursor.getString(3);
         //  String icon = cursor.getString(4);

            Log.d("ContactSelectAdaptor"," " + contact_id + " " + first_name + " " + last_name+ " " + email);

            if (last_name ==null){
                last_name = " ";
            }

            listViewRows.add(new ContactData(contact_id,first_name,last_name,email));
        }

    }

    @Override
    public int getCount() {
        return listViewRows.size();
    }

    @Override
    public Object getItem(int position) {
        return listViewRows.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
       View view = layoutInflater.inflate(R.layout.listview_contact_select,parent,false);

        ImageView imageView = (ImageView) view.findViewById(R.id.imageViewProfile);
        TextView textViewName = (TextView) view.findViewById(R.id.textViewDisplayName);
        TextView textViewEmail = (TextView) view.findViewById(R.id.textViewEmailAddress);
        CheckBox checkBox = (CheckBox) view.findViewById(R.id.checkBoxSelected);

        ContactData contactData = listViewRows.get(position);
        imageView.setImageURI(contactData.getIcon());
        textViewName.setText(contactData.getFirst_name());
        textViewEmail.setText(contactData.getEmail());
        checkBox.setChecked(false);

        return view;
    }


}

我添加了log.d来检查数据是否为null但是它正确地显示如下：

06-03 17:00:37.757    2392-2392/com.project.iandwe D/ContactSelectAdaptor﹕ 3 Batman null bat@gmail.com

我收到以下错误：

06-03 17:00:37.767    2392-2392/com.project.iandwe E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.project.iandwe, PID: 2392
    java.lang.NullPointerException
            at com.project.iandwe.Adaptor.ContactSelectAdaptor.<init>(ContactSelectAdaptor.java:49)
            at com.project.iandwe.Menu.ContactsFragments.onActivityCreated(ContactsFragments.java:42)

错误发生在以下两行代码中：

 listViewRows.add(new ContactData(contact_id,first_name,last_name,email));

这是在ContactSelectAdaptor类中我在片段中通过此方法创建类对象：

 listView.setAdapter(new ContactSelectAdaptor(getActivity()));

我认为错误发生的原因是由于last_name为null或者Uri被设置为null，但即使在这种情况下，ContactData也应该能够创建一个对象。

我正在使用上面的适配器类来填写自定义列表视图。请让我知道我在这里缺少什么

Answer 1

它为null，因为您没有实例化listViewRows。

<强>溶液

在添加到ArrayList

之前先实例化它

listViewRows = new ArrayList<ContactData>();

Answer 2

listViewRows被宣布：

ArrayList<ContactData> listViewRows;

...但是从未初始化，这将导致空指针。

Null Pointer创建在适配器中用于填充自定义列表视图的类对象时出现异常

2 个答案: