Question

我有一个奇怪的问题，似乎无法找到导致它的原因。我的ArrayAdapter中的每个视图组件都位于getView方法中，除了我的按钮，它导致NullPointerException。

适配器：

public class ItemAdapter extends ArrayAdapter<Item>{

private Context context;
private int resource;
private List<Item> list;

public ItemAdapter(Context context, int resource, List<Item> list) 
{
    super(context, resource, list);
    this.context = context;
    this.resource = resource;
    this.list = list;
}


@Override
public View getView(int position, View convertView, ViewGroup parent) 
{
    if (convertView == null)
        convertView = LayoutInflater.from(context).inflate(resource, parent,false);

    TextView name = (TextView) convertView.findViewById(R.id.itemName);
    ImageView itemImg = (ImageView) convertView.findViewById(R.id.itemImg);
    Button addToCart = (Button) convertView.findViewById(R.id.button1);

    final Item item = list.get(position);
    name.setText(item.getName());

    UrlImageViewHelper.setUrlDrawable(itemImg, item.getPicture());
    addToCart.setOnClickListener(new OnClickListener(){
        @Override
        public void onClick(View view) 
        {
            Toast.makeText(context, "Clicked", Toast.LENGTH_LONG).show();
        }
    });
    return convertView;
}

}

使用listview的片段

    @InjectView(R.id.itemList)   private ListView listView;
@Inject private ItemDao dao;

private ArrayAdapter<Item> adapter;

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{   
    return inflater.inflate(R.layout.fragment_shop, container, false);
}


@Override
public void onViewCreated(View view, Bundle savedInstanceState) 
{
    super.onViewCreated(view, savedInstanceState);
    dao.open();
    List<Item> items = dao.findAll();
    dao.close();

    adapter = new ItemAdapter(getActivity(),R.layout.list_product_item, items);
    listView.setAdapter(adapter);
}

list_product_item

<?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"
android:orientation="horizontal"
android:paddingBottom="5dp"
android:paddingLeft="10dp"
android:paddingRight="10dp"
android:paddingTop="5dp" >

<ImageView
    android:id="@+id/itemImg"
    android:layout_width="100dp"
    android:layout_height="100dp"
    android:layout_marginRight="5dp"
    android:scaleType="centerCrop" />

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/itemName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Medium Text"
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <TextView
        android:id="@+id/itemStoreName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView" />

    <Button
        android:id="@+id/button1"
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button" />

</LinearLayout>

现在对convertView.findViewById（R.id.button1）的调用返回一个null实例。造成这种情况的原因是什么？如何解决？

Answer 1

你有正确的布局名称吗？

adapter = new GroceryItemAdapter（getActivity（）， R.layout.list_textview ，items）;

VS

list_product_item

（我假设这是 R.layout.list_product_item 的文件名）

Answer 2

不是使用from方法获取布局inflater而是尝试在构造函数中初始化inflater。

  mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

getView

中的

    convertView = mInflater.inflate(your layout, null);

获取按钮时ListView中的NullPointErexception

2 个答案: