java RecycleServiceAdapter OnBindViewHolder具有空ID
我正在编写一个天气预报应用程序，我想尝试实现一个RecyclerView，这样我就可以拥有一个侧面滚动的ListView。但是，当我设置文本时，我的onBindViewHolder（）会抛出NPE，因为视图ID为null，即使创建ViewHolder时ID不是null。如果能帮我找出差异，我将不胜感激。谢谢大家!
我的代码如下：
主要活动：
public class MainActivity extends AppCompatActivity {
EditText searchText;
Button searchButton;
Context context;
int count = 1; // default to one - potentially change later
RecyclerView recyclerView;
天气适配器； ArrayList天气表
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
context = this;
recyclerView = (RecyclerView)findViewById(R.id.recyclerViewID);
LinearLayoutManager manager = new LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false);
recyclerView.setLayoutManager(manager);
adapter = new WeatherAdapter(context, weatherList);
recyclerView.setAdapter(adapter);
searchText = (EditText) findViewById(R.id.citySearchID);
searchButton = (Button) findViewById(R.id.searchButtonID);
searchButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) { startSearch(view); }
});
}
public void startSearch(View view) {
JSONWeatherTask task = new JSONWeatherTask();
String s = searchText.getText().toString();
if (s.isEmpty()){
Toast.makeText(this, R.string.searchError, Toast.LENGTH_SHORT).show();
return;
}
try{ task.execute(s.replaceAll("\\s+", ""));
} catch (Exception e) {
Toast.makeText(this, R.string.searchError, Toast.LENGTH_SHORT).show();
}
}
private class JSONWeatherTask extends AsyncTask<String, Void, ArrayList<Weather>> {
@Override
protected ArrayList<Weather> doInBackground(String... strings) {
weatherList = new ArrayList<>();
JSONObject jObj = ((new WeatherHttpClient()).getWeatherData(strings[0], count));
try { weatherList = JSONWeatherParser.getWeather(jObj, count);
} catch (JSONException e) { e.printStackTrace(); }
return weatherList;
}
@Override
protected void onPostExecute(ArrayList<Weather> weatherList) {
super.onPostExecute(weatherList);
LinearLayoutManager manager = new LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false);
recyclerView.setLayoutManager(manager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
adapter = new WeatherAdapter(context, weatherList);
recyclerView.setAdapter(adapter);
}
}
}
适配器：
public class WeatherAdapter extends RecyclerView.Adapter<ViewHolder> {
private final Context context;
private final ArrayList<Weather> weatherList;
public WeatherAdapter(Context context, ArrayList<Weather> weatherList){
this.context = context;
this.weatherList = weatherList;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType){
LayoutInflater infl = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v = infl.inflate(R.layout.weather_row, null);
ViewHolder holder = new ViewHolder(v);
return holder;
}
@Override
public void onBindViewHolder(ViewHolder holder, int pos){
Weather weather = weatherList.get(pos);
String[] Days = {"SUNDAY", "MONDAY", "TUESDAY", "WEDNESDAY", "THURSDAY", "FRIDAY", "SATURDAY"};
long unixSeconds = weather.currentCondition.getDate();
Date date = new Date(unixSeconds * 1000L);
SimpleDateFormat dateFormat = new SimpleDateFormat("MMM dd");
String formattedDate = dateFormat.format(date);
Calendar cal = Calendar.getInstance();
cal.setTimeInMillis(unixSeconds * 1000L);
holder.dateText.setText(formattedDate);
holder.dayText.setText(Days[cal.get(Calendar.DAY_OF_WEEK)-1]);
// set other TextViews in the same way
}
@Override
public int getItemCount() {
try{ return weatherList.size();
} catch (NullPointerException e) { return 0; }
}
}
持证人：
public class ViewHolder extends RecyclerView.ViewHolder{
TextView dateText;
TextView dayText;
// Other TextViews in the same vein
public ViewHolder (View view){
super(view);
TextView dateText = (TextView)view.findViewById(R.id.dateTextID);
TextView dayText = (TextView)view.findViewById(R.id.dayTextID);
// Other TextViews in the same vein
}
}
自定义行xml:
<LinearLayout xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
安卓:orientation="vertical"
安卓:layout_width="match_parent"
安卓:layout_height="match_parent">
<TextView
安卓:id="@+id/dateTextID"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content" />
<TextView
安卓:id="@+id/dayTextID"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content" />
<!-- Etc with more TextViews -->
</LinearLayout>
主要活动xml：
<LinearLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:orientation="horizontal">
<EditText
安卓:id="@+id/citySearchID"
安卓:layout_width="0dp"
安卓:layout_height="wrap_content"
安卓:layout_weight="3"
安卓:inputType="text"
安卓:hint="@string/cityHint"/>
<Button
安卓:id="@+id/searchButtonID"
安卓:layout_width="0dp"
安卓:layout_height="wrap_content"
安卓:layout_gravity="end"
安卓:layout_weight="1"
安卓:text="@string/search"/>
</LinearLayout>
<安卓.support.v7.widget.RecyclerView
安卓:id="@+id/recyclerViewID"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"/>
</LinearLayout>
日志：
java.lang.NullPointerException: Attempt to invoke virtual method 'void 安卓.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.ak.niceweather.WeatherAdapter.onBindViewHolder(WeatherAdapter.java:48)
at com.ak.niceweather.WeatherAdapter.onBindViewHolder(WeatherAdapter.java:17)
at 安卓.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:5217)
at 安卓.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:5250)
at 安卓.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4487)
at 安卓.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4363)
at 安卓.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1961)
at 安卓.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1370)
at 安卓.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1333)
at 安卓.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:562)
at 安卓.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2900)
at 安卓.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3071)
at 安卓.view.View.layout(View.java:15596)
at 安卓.view.ViewGroup.layout(ViewGroup.java:4966)
at 安卓.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
at 安卓.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
at 安卓.widget.LinearLayout.onLayout(LinearLayout.java:1466)
at 安卓.view.View.layout(View.java:15596)
at 安卓.view.ViewGroup.layout(ViewGroup.java:4966)
at 安卓.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at 安卓.widget.FrameLayout.onLayout(FrameLayout.java:508)
at 安卓.view.View.layout(View.java:15596)
at 安卓.view.ViewGroup.layout(ViewGroup.java:4966)
at 安卓.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:435)
at 安卓.view.View.layout(View.java:15596)
at 安卓.view.ViewGroup.layout(ViewGroup.java:4966)
at 安卓.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at 安卓.widget.FrameLayout.onLayout(FrameLayout.java:508)
at 安卓.view.View.layout(View.java:15596)
at 安卓.view.ViewGroup.layout(ViewGroup.java:4966)
at 安卓.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
at 安卓.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
at 安卓.widget.LinearLayout.onLayout(LinearLayout.java:1466)
at 安卓.view.View.layout(View.java:15596)
at 安卓.view.ViewGroup.layout(ViewGroup.java:4966)
at 安卓.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at 安卓.widget.FrameLayout.onLayout(FrameLayout.java:508)
at 安卓.view.View.layout(View.java:15596)
at 安卓.view.ViewGroup.layout(ViewGroup.java:4966)
at 安卓.view.ViewRootImpl.performLayout(ViewRootImpl.java:2072)
at 安卓.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1829)
at 安卓.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
at 安卓.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
at 安卓.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at 安卓.view.Choreographer.doCallbacks(Choreographer.java:580)
at 安卓.view.Choreographer.doFrame(Choreographer.java:550)
at 安卓.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at 安卓.os.Handler.handleCallback(Handler.java:739)
at 安卓.os.Handler.dispatchMessage(Handler.java:95)
at 安卓.os.Looper.loop(Looper.java:135)
at 安卓.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:694)
# 1 楼答案
您的问题在于
ViewHolder.java类。在构造函数中定义和初始化新变量，而不是私有变量。因此，替换与
或者简单地说：