addHeaderView和setAdapter的NullPointerException

时间：2014-02-03 14:14:12

标签： android nullpointerexception custom-lists

  

注意：我提到了类似的问题但仍然找不到任何错误

的NullPointerException 
listView.addHeaderView(header);

和

listView.setAdapter(adapter);

详细代码： 

Veg v = new Veg();
v.setId(1);
v.setName("some");
v.setPrice(15.0);

List<Veg> vegData = new ArrayList<Veg>();

// dummy add for testing 
vegData.add(v);
vegData.add(v);
vegData.add(v);

CustomAdapter adapter = new CustomAdapter(this,
        R.layout.custom_list_rows, vegData);
listView = (ListView) findViewById(R.id.listView1);


View header = getLayoutInflater().inflate(
        R.layout.custom_list_header, null);

listView.addHeaderView(header);

listView.setAdapter(adapter);

getView（）部分 

public class CustomAdapter extends ArrayAdapter<Veg> {

    Context context;
    int layoutResourceId;
    List<Veg> data;

    public CustomAdapter(Context context, int resource, List<Veg> data) {
        super(context, resource);
        this.context = context;
        this.layoutResourceId = resource;
        this.data = data;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View row = convertView;
        CustomHolder holder = null;

        if (row == null) {
            LayoutInflater inflater = ((Activity) context).getLayoutInflater();
            row = inflater.inflate(layoutResourceId, parent, false);

            holder = new CustomHolder();
            holder.at = (TextView) row.findViewById(R.id.customheaderbutton1);
            holder.bt = (TextView) row.findViewById(R.id.customheaderbutton2);
            holder.ct = (TextView) row.findViewById(R.id.customheaderbutton3);
            row.setTag(holder);
        } else {
            holder = (CustomHolder) row.getTag();
        }

        holder.at.setText(String.valueOf(data.get(position).getId()));
        holder.bt.setText(data.get(position).getName());
        holder.ct.setText(String.valueOf(data.get(position).getPrice()));

        return row;
    }

    static class CustomHolder {
        TextView at;
        TextView bt;
        TextView ct;
    }

}

主要活动xml文件 

 <?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"
    android:background="#FFFFFF"> 

     <ListView
        android:id="@+id/listView1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />

</LinearLayout>

custom_list_header.xml 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="horizontal" >

    <Button
        android:id="@+id/customheaderbutton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0.8"
        android:text="marketname" />

    <Button
        android:id="@+id/customheaderbutton2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0.1"
        android:text="edit" />

    <Button
        android:id="@+id/customheaderbutton3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0.1"
        android:text="+" />

</LinearLayout>

custom_list_rows.xml 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <TextView
        android:id="@+id/elementIDtext"
        android:layout_width="11dp"
        android:layout_height="wrap_content"
        android:text=""
        android:textAppearance="?android:attr/textAppearanceSmall" />

    <TextView
        android:id="@+id/elementName"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="0.30"
        android:text="@string/elementName"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <TextView
        android:id="@+id/elementSummary"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/elementValue"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <Button
        android:id="@+id/button1"
        android:layout_width="62dp"
        android:layout_height="wrap_content"
        android:text="@string/_" />

</LinearLayout>

3 个答案:

答案 0 :(得分：1)

listView似乎null，这意味着findViewById()返回了null：它无法找到您正在寻找的控件。如果没有看到您的布局，就无法进一步调试，但请确保R.id.listView1指的是有效元素。

答案 1 :(得分：1)

在getView中，更改

    holder.at = (TextView) row.findViewById(R.id.customheaderbutton1);
    holder.bt = (TextView) row.findViewById(R.id.customheaderbutton2);
    holder.ct = (TextView) row.findViewById(R.id.customheaderbutton3);

到

    holder.at = (TextView) row.findViewById(R.id.elementIDtext);
    holder.bt = (TextView) row.findViewById(R.id.elementName);
    holder.ct = (TextView) row.findViewById(R.id.elementSummary);

答案 2 :(得分：0)

用以下代码替换您的代码： 

package com.example.listview;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

public class List extends Activity 
{
    private ListView listview;
    Veg Veg = new Veg(); 
    ArrayList<Veg> data = new ArrayList<Veg>();
    CustomAdapter adapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list);

        listview = (ListView)findViewById(R.id.listView);

        for(int i=1;i<101;i++)
        {
            Veg = new Veg();
            Veg.setName("Item "+i);
            Veg.setID("ID "+i);
            Veg.setPrice("Price "+i);

            data.add(Veg);
        }

         View headerView = getLayoutInflater().inflate(
                    R.layout.custom_list_header, null);


                listview.addHeaderView(headerView);

                adapter = new CustomAdapter(this,R.layout.custom_list_rows,data);
                listview.setAdapter(adapter);
    }

    class CustomAdapter extends ArrayAdapter<Veg>
    {
        Context con;
        int Res;
        ArrayList<Veg> data;
        public CustomAdapter(Context context, int resource, ArrayList<Veg> data) {
            super(context, resource,data);
            // TODO Auto-generated constructor stub
            con = context;
            Res = resource;
            this.data = data;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View row = convertView;
            CustomHolder holder = null;

            if (row == null) {
                LayoutInflater inflater = getLayoutInflater();
                row = inflater.inflate(Res, parent, false);

                holder = new CustomHolder();
                holder.at = (TextView) row.findViewById(R.id.elementIDtext);
                holder.bt = (TextView) row.findViewById(R.id.elementName);
                holder.ct = (TextView) row.findViewById(R.id.elementSummary);
                row.setTag(holder);
            } else {
                holder = (CustomHolder) row.getTag();
            }

            holder.at.setText(String.valueOf(data.get(position).getID()));
            holder.bt.setText(data.get(position).getName());
            holder.ct.setText(String.valueOf(data.get(position).getPrice()));

            return row;
        }

        class CustomHolder {
            TextView at;
            TextView bt;
            TextView ct;
        }

    }
}

此外，您必须更改您的XML，如下所示，而不是像11 dp那样给出静态宽度。

<强> custom_list_rows.xml 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="horizontal" >

    <TextView
        android:id="@+id/elementIDtext"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="ID"
        android:gravity="center"
        android:textAppearance="?android:attr/textAppearanceSmall" />

    <TextView
        android:id="@+id/elementName"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="elementName"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <TextView
        android:id="@+id/elementSummary"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="elementValue"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <Button
        android:id="@+id/button1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="btn" />

</LinearLayout>
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