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私は天気予報アプリを作成しています。私は本質的にサイドスクロールListViewを持つことができるようにRecyclerViewを実装しようと思っていました。しかし、ViewHolderの作成時にIDがnullではないにもかかわらず、ビューIDがnullであるためにテキストを設定すると、onBindViewHolder（）がNPEをスローします。私は矛盾を見つけるのに助けていただければ幸いです。ありがとうございました！次のようにRecyclerViewAdapter OnBindViewHolderにヌルIDがある
私のコードは次のとおりです。
MainActivity：
public class MainActivity extends AppCompatActivity {
EditText searchText;
Button searchButton;
Context context;
int count = 1; // default to one - potentially change later
RecyclerView recyclerView;
WeatherAdapterアダプタ。 ArrayList weatherList;
@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);
}
}
}
アダプタ：
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; }
}
}
ViewHolder：
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
}
}
CustomRowのXML：
<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:id="@+id/dateTextID"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/dayTextID"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<!-- Etc with more TextViews -->
</LinearLayout>
MainActivityのXML：
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<EditText
android:id="@+id/citySearchID"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="3"
android:inputType="text"
android:hint="@string/cityHint"/>
<Button
android:id="@+id/searchButtonID"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_gravity="end"
android:layout_weight="1"
android:text="@string/search"/>
</LinearLayout>
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerViewID"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
Logcat：
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.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 android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:5217)
at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:5250)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4487)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4363)
at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1961)
at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1370)
at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1333)
at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:562)
at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2900)
at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3071)
at android.view.View.layout(View.java:15596)
at android.view.ViewGroup.layout(ViewGroup.java:4966)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
at android.view.View.layout(View.java:15596)
at android.view.ViewGroup.layout(ViewGroup.java:4966)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
at android.view.View.layout(View.java:15596)
at android.view.ViewGroup.layout(ViewGroup.java:4966)
at android.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:435)
at android.view.View.layout(View.java:15596)
at android.view.ViewGroup.layout(ViewGroup.java:4966)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
at android.view.View.layout(View.java:15596)
at android.view.ViewGroup.layout(ViewGroup.java:4966)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
at android.view.View.layout(View.java:15596)
at android.view.ViewGroup.layout(ViewGroup.java:4966)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
at android.view.View.layout(View.java:15596)
at android.view.ViewGroup.layout(ViewGroup.java:4966)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2072)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1829)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at android.view.Choreographer.doCallbacks(Choreographer.java:580)
at android.view.Choreographer.doFrame(Choreographer.java:550)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.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.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)