Question

我正在为学校开发一个应用程序，我必须创建一个购物清单，当我选择一个列表时，我应该在该列表中获得一个新的活动。现在我的问题是，当我尝试获取listView中的clicked元素，然后将产品放在新活动的listview中的列表中时，我在textview上得到一个空指针异常。

这是获取异常的文本视图

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

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:textSize="20dp"
        android:textColor="#236B8E"
        android:layout_marginTop="20dp"
        android:id="@+id/products_on_list"/>
</LinearLayout>

这是我新活动中的listView：

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

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

</LinearLayout>

以下是新活动的java代码：

public class DisplayShoppingListDetailsActivity extends AppCompatActivity{


 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //defines the activity layout
        setContentView(R.layout.shopping_list_details);

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

        Intent intent = getIntent();
        String name = intent.getStringExtra("list");

        ProductsOnListAdapter ad = new ProductsOnListAdapter(this, -1, Service.getService().getProductsOnList(name));
        listView.setAdapter(ad);

    }
}

这是我有购物清单列表的片段。这是我为新活动创建意图的地方：

public class Fragment1 extends Fragment {
    public Fragment1() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        final View rootView = inflater.inflate(R.layout.fragment1, container, false);

        final ListView listView = (ListView) rootView.findViewById(R.id.listView_shopping_lists);
        // get data from the table by the ListAdapter
        ShoppingListAdapter listAdapter = new ShoppingListAdapter(getActivity(), -1, Service.getService().getShoppingLists());
        listView.setAdapter(listAdapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {

                // selected item
                // HERE IS THE PROBLEM 
                // I have tried to use rootView instead of view
                TextView textview = (TextView) view.findViewById(R.id.products_on_list);
                String list = textview.getText().toString();

                // Launching new Activity on selecting single List Item
                Intent intent = new Intent(getActivity(), DisplayShoppingListDetailsActivity.class);
                // sending data to new activity
                intent.putExtra("list", list);
                startActivity(intent);

            }
        });

        //System.out.println("Test: " + Storage.getStorage().getShopingLists());
        return rootView;
    }
}

这是例外：

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.widget.TextView.getText()' on a null object reference
at com.gnirt69.slidingmenuexample.fragment.Fragment1$1.onItemClick(Fragment1.java:44)

ShoppingListAdapter：

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

        // Get the data item for this position
        //final ShoppingList list = getItem(position);
        ViewHolder holder;

        // Check if an existing view is being reused, otherwise inflate the view
        if (convertView == null) {
            convertView = View.inflate(getContext(), R.layout.items_lists_row, null);

            //set up the viewHolder
            holder = new ViewHolder();
            holder.shoppingListTextView = (TextView) convertView.findViewById(R.id.textView1);
            convertView.setTag(holder);
        }else{
            holder = (ViewHolder) convertView.getTag();
        }

        // get the reference to the specific item
        final ShoppingList list = getItem(position);
        //TextView tv = (TextView) convertView.findViewById(R.id.textView1);

        //manipulate the view
        holder.shoppingListTextView.setText(list.getName());

        return convertView;
    }

    public static class ViewHolder {
        private TextView shoppingListTextView;
    }

=======解决空指针后编辑=======

现在它会打开新活动但它是空的，它不会填充列表视图。我正在努力弄清楚我到底在做错什么。

这是我的片段：

 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        final View rootView = inflater.inflate(R.layout.fragment1, container, false);

        final ListView listView = (ListView) rootView.findViewById(R.id.listView_shopping_lists);
        // get data from the table by the ListAdapter
        final ShoppingListAdapter listAdapter = new ShoppingListAdapter(getActivity(), -1, Service.getService().getShoppingLists());
        listView.setAdapter(listAdapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {

                ShoppingList shoppingList = listAdapter.getItem(position);

                // selected item
                TextView textview = (TextView) rootView.findViewById(R.id.products_on_list);
                String list = textview.getText().toString();

                // Launching new Activity on selecting single List Item
                Intent intent = new Intent(getActivity(), DisplayShoppingListDetailsActivity.class);
                // sending data to new activity
                intent.putExtra("list", list);
                //System.out.println(shoppingList.getProductsOnList());
                startActivity(intent);

            }
        });

        //System.out.println("Test: " + Storage.getStorage().getShopingLists());
        return rootView;
    }

应该在点击列表中显示产品的新活动，但不会：

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //defines the activity layout
        setContentView(R.layout.shopping_list_details);

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

        Intent intent = getIntent();
        String name = intent.getStringExtra("list");

        ProductsOnListAdapter ad = new ProductsOnListAdapter(this, -1, Service.getService().getProductsOnList(name));
        listView.setAdapter(ad);

    }

适配器：

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

        // Get the data item for this position
        //final ShoppingList list = getItem(position);
        ViewHolder holder;

        // Check if an existing view is being reused, otherwise inflate the view
        if (convertView == null) {
            convertView = View.inflate(getContext(), R.layout.shopping_list_details, null);

            //set up the viewHolder
            holder = new ViewHolder();
            holder.productsTextView = (TextView) convertView.findViewById(R.id.products_on_list);
            convertView.setTag(holder);
        }else{
            holder = (ViewHolder) convertView.getTag();
        }

        // get the reference to the specific item
        final ProductOnList product = getItem(position);
        //TextView tv = (TextView) convertView.findViewById(R.id.textView1);

        //manipulate the view
        holder.productsTextView.setText(product.toString());

        return convertView;
    }

    public static class ViewHolder {
        private TextView productsTextView;
    }

Answer 1

我认为问题是你想从布局

调用Textview

setContentView(R.layout.shopping_list_details);

但你的片段使用了布局

final View rootView = inflater.inflate(R.layout.fragment1, container, false);

您可以通过将TextView从Main传递到Fragment或更改xml布局来解决此问题

您可以通过向fragment1布局添加具有相同ID的textview来测试是否为真。

Answer 2

您在新Activity和Fragment中引用相同的ListView R.id.listView_shopping_lists，您从不在Activity布局文件中定位shopping_list_details，其中包含每个项目，因此TextView为null。

android中textView上的空指针异常

2 个答案: