Question

编辑：显然我的问题被标记为重复，事情是我花了很多时间在stackoverflow上寻找解决方案，然后发布我的问题。我的问题不是“什么是空指针异常”请帮助

noob在这里，我正在学习如何使用适配器来填充ListView，当我尝试使用它时，我的自定义适配器出现问题App崩溃并给了我这个错误：

java.lang.NullPointerException
at android.widget.AbsListView.obtainView(AbsListView.java:2265)

然而，当我尝试使用ArrayAdatper时，它工作得很好。我怀疑我传递了错误的背景。

请注意我使用片段而不是活动

代码应该将列表视图myCustomListview从虚拟字符串数组dummyValues填充到location布局中的文本字段custom_row

Spendiing

package app.hujair.android.example.com.aou_project_nm;
   import android.os.Bundle;
   import android.support.v4.app.Fragment;
   import android.view.LayoutInflater;
   import android.view.View;
   import android.view.ViewGroup;
   import android.widget.ArrayAdapter;
   import android.widget.ListView;

   public class Spendings extends Fragment {

   View view;

   public Spendings() {
        }


   @Override
   public View onCreateView(LayoutInflater inflater, ViewGroup 
   container,Bundle savedInstanceState) {

   //inflater.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    view = inflater.inflate(R.layout.fragment_spendings, container, false);
       return view;
   }

   @Override
   public void onActivityCreated(Bundle savedInstanceState) {
      super.onActivityCreated(savedInstanceState);


      ListView listView = (ListView)   view.findViewById(R.id.myCustomListview);
      String[] dummyValues = new String[]{"hello", "something"};
      listView = (ListView) view.findViewById(R.id.myCustomListview);

      //CustomAdapter adapter = new   CustomAdapter(getActivity(),dummyValues);


    ArrayAdapter<String> adapter = new ArrayAdapter<String>
    (getActivity(),R.layout.custom_row,R.id.location, dummyValues);
    listView.setAdapter(adapter);


  }


  }

CustomAdapter

package app.hujair.android.example.com.aou_project_nm;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

public class CustomAdapter extends ArrayAdapter<String> {

 CustomAdapter(Context context, String[] transcation_type) {
    super(context,R.layout.custom_row ,transcation_type);

}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflater = LayoutInflater.from(getContext());
    View customView = inflater.inflate(R.layout.custom_row,  parent, false);


    String singleLocation = getItem(position);
    TextView location = (TextView)customView.findViewById(R.id.location);
    location.setText(singleLocation);

    return convertView;
}
}

fragment_spending

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="app.hujair.android.example.com.aou_project_nm.Spendings">

<!-- TODO: Update blank fragment layout -->
<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Total spendings goes here."
    android:gravity="center"
    android:textSize="35dp"
    android:textStyle="bold"
    android:layout_marginTop="20dp"
    android:id="@+id/Spending_text"
    />

<ListView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/myCustomListview"
    android:layout_marginTop="15dp"
    android:layout_below="@+id/Spending_text"
    android:divider="@null"
    ></ListView>


</RelativeLayout>

custom_row

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



<ImageView
    android:layout_marginTop="35dp"
    android:layout_marginLeft="25dp"
    android:layout_width="35dp"
    android:layout_height="35dp"
    android:id="@+id/custom_row_icon"
    android:src="@drawable/minus_circle"/>

<TextView

    android:layout_marginTop="-2dp"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="note note note note ..."
    android:textSize="15dp"
    android:id="@+id/note"
    android:layout_alignTop="@+id/amount"
    android:layout_alignStart="@+id/location" />


<TextView
    android:layout_alignParentRight="true"
    android:gravity="right"
    android:layout_marginTop="32dp"
    android:layout_marginRight="25dp"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Amount"
    android:textSize="18dp"
    android:id="@+id/amount"/>

<TextView
    android:layout_marginTop="-8dp"
    android:layout_below="@+id/amount"
    android:layout_marginLeft="10dp"
    android:layout_toRightOf="@+id/custom_row_icon"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="location"
    android:textSize="12dp"
    android:id="@+id/location" />

<TextView
    android:layout_marginTop="-2dp"
    android:layout_below="@+id/location"
    android:layout_marginLeft="10dp"

    android:layout_toRightOf="@+id/custom_row_icon"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="time"
    android:textSize="12dp"
    android:id="@+id/time" />


</RelativeLayout>

Answer 1

从getView返回null，必须返回customView

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflater = LayoutInflater.from(getContext());
    View customView = inflater.inflate(R.layout.custom_row,  parent, false);


    String singleLocation = getItem(position);
    TextView location = (TextView)customView.findViewById(R.id.location);
    location.setText(singleLocation);

    return customView;
}

无法使自定义适配器在片段

1 个答案: