问题描述

ListView 的问题，按照书上例子，仿写了一个，结果出问题了，请大家看看到底哪里出错了啊

先是有两个布局文件，一个是关于ListView控件的，另一个是我自己定的线性布局，实现的是一个字符旁边先是一个图样。
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.IWIN.listview.MainActivity" >

<ListView
    android:id="@+id/listView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    />

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

<ImageView
    android:id="@+id/image"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
   />
<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"

    android:layout_marginLeft="10dp"/>

然后定义了一个了类，定义字符和图样
package com.IWIN.listview;

public class Fruit {
private String name;
private int imageId;
public Fruit(String name,int imageId){
this.name=name;
this.imageId=imageId;
}
public int getImageId(){
return imageId;
}
public String getName(){
return name;
}

}

紧接着又定义了一个适配器
package com.IWIN.listview;

import java.util.List;

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

import com.IWIN.listview.Fruit;
import com.IWIN.listview.R;

public class FruitAdapter extends ArrayAdapter{

            private ImageView image;
            private TextView  textView;
            int resourceId;
public FruitAdapter(Context context, int textViewResourceId,
        List<Fruit> objects) {
    super(context,  textViewResourceId, objects);
    resourceId=textViewResourceId;

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

    Fruit fruit=getItem(position);//找到在屏幕内的fruit类
    View view=LayoutInflater.from(getContext()).inflate(resourceId,null);//cetContentView是Activity里面的类
    image=(ImageView)view.findViewById(R.id.image);                     //LayoutInflater.from().inflate(常量ID,ViewGroup)可以在非Activity里面使用。
    textView=(TextView)view.findViewById(R.id.textView);
    image.setImageResource(fruit.getImageId());
    textView.setText(fruit.getName());
    return view;

}

}

再然后就是ManiActivity
private ListView listView;

protected void onCreate(Bundle savedInstanceState) {
    nitFruit();
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
   FruitAdapter adapter=new FruitAdapter(MainActivity.this,android.R.layout.simple_list_item_1,list);
    listView=(ListView)findViewById(R.id.listView);
    listView.setAdapter(adapter);
}

public void nitFruit(){
    Fruit read=new Fruit("read",R.drawable.ic_launcher);
    list.add(read);
    Fruit write=new Fruit("write",R.drawable.ic_launcher);
    list.add(write);
    Fruit white=new Fruit("white",R.drawable.ic_launcher);
    list.add(white);
    Fruit blue=new Fruit("blue",R.drawable.ic_launcher);
    list.add(blue);
    Fruit sea=new Fruit("sea",R.drawable.ic_launcher);
    list.add(sea);
    Fruit like=new Fruit("like",R.drawable.ic_launcher);
    list.add(like);
    Fruit love=new Fruit("love",R.drawable.ic_launcher);
    list.add(love);
    Fruit student=new Fruit("student",R.drawable.ic_launcher);
    list.add(student);
    Fruit teacher=new Fruit("teacher",R.drawable.ic_launcher);
    list.add(teacher);
    Fruit classmates=new Fruit("classmates",R.drawable.ic_launcher);
    list.add(classmates);
    Fruit classroom=new Fruit("classroom",R.drawable.ic_launcher);
    list.add(classroom);
    Fruit hello=new Fruit("hello",R.drawable.ic_launcher);
    list.add(hello);
}

}

编译后LogCat显示的错误，我也没看出问题

09-11 02:45:16.776: W/dalvikvm(844): threadid=1: thread exiting with uncaught exception (group=0x409bf1f8)
09-11 02:45:16.796: E/AndroidRuntime(844): FATAL EXCEPTION: main
09-11 02:45:16.796: E/AndroidRuntime(844): java.lang.NullPointerException
09-11 02:45:16.796: E/AndroidRuntime(844): at com.IWIN.listview.FruitAdapter.getView(FruitAdapter.java:34)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.widget.AbsListView.obtainView(AbsListView.java:2033)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.widget.ListView.makeAndAddView(ListView.java:1772)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.widget.ListView.fillDown(ListView.java:672)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.widget.ListView.fillFromTop(ListView.java:732)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.widget.ListView.layoutChildren(ListView.java:1625)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.widget.AbsListView.onLayout(AbsListView.java:1863)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.view.View.layout(View.java:11278)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.view.ViewGroup.layout(ViewGroup.java:4224)
09-11 02:45:16.796: E/AndroidRuntime(844): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1628)
。。。。。。

解决方案

你传入的resourecid不对，要传你自己写的包含一个textview和imageview的那个布局的id。你传的是系统的android.R.layout.simple_list_item_1，这玩意儿就一个textview，而且id应该是text。没有imageview。所以是在image.setImageResource(fruit.getImageId());这里空指针。因为image没找到

解决方案二：

空指针报错，View view=LayoutInflater.from(getContext()).inflate(resourceId,null)终得resourecid没有指定吧

解决方案三：

com.IWIN.listview.FruitAdapter.getView(FruitAdapter.java:34)报错了。

  FruitAdapter adapter=new FruitAdapter(MainActivity.this,android.R.layout.simple_list_item_1,list);//在MainActivity里面的第二个参数不对,你要传递你自己的layout.

解决方案四：

convertView没赋值？