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Ich schreibe eine Wettervorhersage App und ich wollte versuchen, eine RecyclerView zu implementieren, so dass ich im Wesentlichen eine Side-Scroll-ListView haben kann. Wie dem auch sei, onBindViewHolder() löst NPEs aus, wenn ich den Text aufgrund von View-IDs auf null gesetzt habe, obwohl die ID beim Erstellen des ViewHolders nicht null ist. Ich würde jede mögliche Hilfe bei der Entdeckung der Diskrepanz schätzen. Vielen Dank!RecyclerViewAdapter OnBindViewHolder hat null IDs
Mein Code ist wie folgt:
MainActivity:
public class MainActivity extends AppCompatActivity {
EditText searchText;
Button searchButton;
Context context;
int count = 1; // default to one - potentially change later
RecyclerView recyclerView;
WeatherAdapter Adapter; 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);
}
}
}
Adapter:
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 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 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)