【发布时间】：2018-02-15 08:33:33
【问题描述】：
我正在编写此代码以在 android 中拥有一个自定义列表。我正在使用
'com.android.support:support-v4:26.1.0'
我当前的代码试图显示一个包含图像和文本的listview，但我想这并不重要。
FourthFragment.java
public class FourthFragment extends ListFragment {
private ArrayList<Weather> weatherProperties = new ArrayList<>();
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View myFragmentView = inflater.inflate(R.layout.fragment_fourth, container, false);
//create our property elements
weatherProperties.add(new Weather(10, "Smith Street", "Sydney", "NSW", "A large 3 bedroom apartment right in the heart of Sydney! A rare find, with 3 bedrooms and a secured car park.", 450.00, "property_image_1", 3, 1, 1));
weatherProperties.add(new Weather(66, "King Street", "Sydney", "NSW", "A fully furnished studio apartment overlooking the harbour. Minutes from the CBD and next to transport, this is a perfect set-up for city living.", 320.00, "property_image_2", 1, 1, 1));
weatherProperties.add(new Weather(1, "Liverpool Road", "Liverpool", "NSW", "A standard 3 bedroom house in the suburbs. With room for several cars and right next to shops this is perfect for new families.", 360.00, "property_image_3", 3, 2, 2));
weatherProperties.add(new Weather(567, "Sunny Street", "Gold Coast", "QLD", "Come and see this amazing studio apartment in the heart of the gold coast, featuring stunning waterfront views.", 360.00, "property_image_4" , 1, 1, 1));
TextView tv = (TextView) myFragmentView.findViewById(R.id.bedroom);
tv.setText("My Header");
// setListAdapter(new ArrayAdapter<String>(getActivity(),android.R.layout.simple_list_item_1,names));
// New Array Adapters
ArrayAdapter<Weather> adapter = new weatherArrayAdapter(getContext(), 0, weatherProperties);
//Find list view and bind it with the custom adapter
ListView listView = (ListView) tv.findViewById(R.id.customListView);
listView.setAdapter(adapter);
return myFragmentView;
}
@Override
public void onListItemClick(ListView l, View v, int position, long id) {
// on click display the item in toast
Toast.makeText(getActivity(), (String)l.getItemAtPosition(position), Toast.LENGTH_SHORT).show();
}
static FourthFragment newInstance(int num) {
FourthFragment fourthFragment = new FourthFragment();
Bundle args = new Bundle();
args.putInt("num", num);
fourthFragment.setArguments(args);
return fourthFragment;
}
//custom ArrayAdapater
class weatherArrayAdapter extends ArrayAdapter<Weather>{
private Context context;
private List<Weather> weatherProperties;
//constructor, call on creation
public weatherArrayAdapter(Context context, int resource, ArrayList<Weather> objects) {
super(context, resource, objects);
this.context = context;
this.weatherProperties = objects;
}
//called when rendering the list
public View getView(int position, View convertView, ViewGroup parent) {
//get the weather we are displaying
Weather weather = weatherProperties.get(position);
//get the inflater and inflate the XML layout for each item
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
//conditionally inflate either standard or special template
View view;
view = inflater.inflate(R.layout.weather_layout, null);
TextView description = (TextView) view.findViewById(R.id.description);
TextView address = (TextView) view.findViewById(R.id.address);
TextView bedroom = (TextView) view.findViewById(R.id.bedroom);
TextView bathroom = (TextView) view.findViewById(R.id.bathroom);
TextView carspot = (TextView) view.findViewById(R.id.carspot);
TextView price = (TextView) view.findViewById(R.id.price);
ImageView image = (ImageView) view.findViewById(R.id.image);
//set address and description
String completeAddress = weather.getStreetNumber() + " " + weather.getStreetName() + ", " + weather.getSuburb() + ", " + weather.getState();
address.setText(completeAddress);
//display trimmed excerpt for description
int descriptionLength = weather.getDescription().length();
if(descriptionLength >= 100){
String descriptionTrim = weather.getDescription().substring(0, 100) + "...";
description.setText(descriptionTrim);
}else{
description.setText(weather.getDescription());
}
//set price and weather attributes
price.setText("$" + String.valueOf(weather.getPrice()));
bedroom.setText("Bed: " + String.valueOf(weather.getBedrooms()));
bathroom.setText("Bath: " + String.valueOf(weather.getBathrooms()));
carspot.setText("Car: " + String.valueOf(weather.getCarspots()));
//get the image associated with this weather
int imageID = context.getResources().getIdentifier(weather.getImage(), "drawable", context.getPackageName());
image.setImageResource(imageID);
return view;
}
}
}
没有compiletime 错误，但这给了我runtime 错误
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.phocast.FourthFragment.onCreateView(FourthFragment.java:39)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2354)
我在这里做错了什么？
如果你能把问题告诉我，我将不胜感激。
答案和 cmets 后更新
错误在这里：（很抱歉将其作为引用，否则不允许我以mostly code error 提交）
TextView tv = (TextView) myFragmentView.findViewById(R.id.bedroom); tv.setText("My Header");
xml 是：
weather_layout.xml
<?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"
android:orientation="vertical"
android:paddingTop="10dp"
android:paddingBottom="10dp">
<ImageView
android:id="@+id/image"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_marginRight="10dp"
android:contentDescription="Property Image" />
<LinearLayout
android:id="@+id/infoSection"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_toRightOf="@+id/image"
android:orientation="vertical">
<TextView
android:id="@+id/address"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="10dp"
android:text="Street Address"
android:textSize="18sp" />
<TextView
android:id="@+id/description"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="10dp"
android:text="Description"
android:textSize="15sp" />
</LinearLayout>
<RelativeLayout
android:id="@+id/pricingSection"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/infoSection"
android:orientation="vertical">
<TextView
android:id="@+id/price"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="10dp"
android:text="Price" />
<TextView
android:id="@+id/bedroom"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/price"
android:layout_marginRight="15dp"
android:text="Bed:" />
<TextView
android:id="@+id/bathroom"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/price"
android:layout_marginRight="15dp"
android:layout_toRightOf="@id/bedroom"
android:text="Bath:" />
<TextView
android:id="@+id/carspot"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/price"
android:layout_marginRight="15dp"
android:layout_toRightOf="@id/bathroom"
android:text="Car:" />
</RelativeLayout>
</RelativeLayout>
更新 2：fragment_four.xml
<?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"
android:background="@color/colorPrimaryLight">
<ListView
android:id="@+id/customListView"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_centerHorizontal="true"
android:layout_alignParentStart="true"
android:scrollbars="vertical"
android:textAlignment="gravity">
</ListView>
</RelativeLayout>
更新3 所以，我创建了一个 fourth_fragment.xml 为：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="@color/colorPrimaryLight">
<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="10dp"
android:text="Description"
android:textSize="15sp" />
<ListView
android:id="@+id/customListView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:layout_centerHorizontal="true"
android:scrollbars="vertical"
android:textAlignment="gravity"></ListView>
</LinearLayout>
并改行：
tv = (TextView) myFragmentView.findViewById(R.id.textView);
tv.setText("My Header");
但我仍然收到错误：
java.lang.NullPointerException: 尝试调用虚方法 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' 空对象引用
【问题讨论】：
-
FourthFragment 课程的第 39 行是什么？
-
您在哪一行出现错误，请发布该行代码@BaRud
-
发布 R.layout.weather_layout xml 并检查 textview id。什么是 tv.findViewById(R.id.customListView);
-
请检查您的布局
R.layout.fragment_fourth是否有指定的id即R.id.bedroom -
你能发布你的'fragment_fourth.xml'吗
标签： java android listadapter