Question

我正在尝试用android中的自定义适配器编写ListView。当我的代码完成时，我得到了'java.lang.NullPointerException'。我一次又一次检查但无法修复此错误。

这是MainActivity代码：

xcode-select: error: command line tools are already installed, use "Software Update" to install updates

在MainActivity代码中

我创建了转到HomeActivity的意图。 HomeActivity代码：

package com.example.sayres.myapplication3_listview;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity{

private EditText mainActivity_editText_userName, mainActivity_editText_password;
private Button mainActivity_btn_login, mainActivity_btn_exit;

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

    initView();
}

private void initView() {
    mainActivity_editText_userName = (EditText) findViewById(R.id.mainActivity_editText_userName);
    mainActivity_editText_password = (EditText) findViewById(R.id.mainActivity_editText_password);
    mainActivity_btn_login = (Button) findViewById(R.id.mainActivity_btn_login);
    mainActivity_btn_exit = (Button) findViewById(R.id.mainActivity_btn_exit);

    mainActivity_btn_exit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            finish();
        }
    });
    mainActivity_btn_login.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            loginprocess();
        }
    });
}



private void loginprocess() {
    String userName = mainActivity_editText_userName.getText().toString();
    String password = mainActivity_editText_password.getText().toString();
    Log.i("====>", "UserName= "+ userName+" Passwotd: "+ password);
    Toast.makeText(getApplicationContext(),userName, Toast.LENGTH_SHORT).show();
    Intent intent = new Intent(getApplicationContext(), HomeActivity.class);
    startActivity(intent);
}
}

我在这行中遇到错误：package com.example.sayres.myapplication3_listview; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.widget.ListView; import com.example.sayres.myapplication3_listview.adapter.ContactAdapter; import com.example.sayres.myapplication3_listview.model.Contact; import java.util.List; public class HomeActivity extends AppCompatActivity { private ListView listViewHome; private List<Contact> contacts; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_home); initViews(); } private void initViews() { listViewHome = (ListView) findViewById(R.id.listViewHome); for (int i = 0; i < 1000; i++) { int pic = 0; if (i % 2 == 0) { pic = R.drawable.man; } else { pic = R.drawable.female; } contacts.add(createContact("name " + i, "family " + i, "5526576", pic)); } ContactAdapter adapter = new ContactAdapter(this, R.layout.row_contacts_list, contacts); listViewHome.setAdapter(adapter); } private Contact createContact(String name, String family, String number, int picture) { return new Contact(name, family, number, picture); } } 这个错误 contacts.add(createContact("name " + i, "family " + i, "5526576", pic));

这是ContactAdapter扩展ArrayAdapter代码：

at com.example.sayres.myapplication3_listview.HomeActivity.initViews(HomeActivity.java:34)
                                                                                                at com.example.sayres.myapplication3_listview.HomeActivity.onCreate(HomeActivity.java:21)

我的Contact类是一个带有setter和getter的简单类：

package com.example.sayres.myapplication3_listview.adapter;

import android.content.Context;
import android.graphics.Color;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import com.example.sayres.myapplication3_listview.R;
import com.example.sayres.myapplication3_listview.model.Contact;

import java.util.List;

import de.hdodenhof.circleimageview.CircleImageView;


public class ContactAdapter extends ArrayAdapter<Contact> {

private Context context;
private int layout;
private List<Contact> contacts;

public ContactAdapter(Context context, int layout, List<Contact> contacts) {
    super(context, layout, contacts);
    this.context = context;
    this.layout = layout;
    this.contacts = contacts;

}

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

    LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View rootView = inflater.inflate(layout, null);


    if (position % 2 == 0 ){
        rootView.setBackgroundColor(Color.parseColor("#12ffff"));
    }else {
        rootView.setBackgroundColor(Color.parseColor("#FFFF12"));

    }

    /**
     * set reference from row_contacts_list.xml
     */
    TextView contactList_name = (TextView) rootView.findViewById(R.id.contactList_name);
    TextView contactList_family = (TextView) rootView.findViewById(R.id.contactList_family);
    CircleImageView profile_picture = (CircleImageView) rootView.findViewById(R.id.profile_picture);

    contactList_name.setText(contacts.get(position).getContactName());
    contactList_family.setText(contacts.get(position).getContactFamily());
    profile_picture.setImageResource(contacts.get(position).getContactPicture());

    return rootView;
}
}

我的错误在哪里？

Answer 1

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home);
    // Init the contacts
    contacts = new ArrayList<Contact>();

    initViews();
}

java中自定义ArrayAdapter中的java.lang.NullPointerException

1 个答案: