Recyclerview适配器错误:Android studio中的数组列表大小为零

Question

首先为我糟糕的英语道歉。我的问题是，我正在尝试使用天气API制作天气应用程序。我想使用recyclerview适配器显示5天的预报。我将数据添加到数组列表中，我从API获得数据它应该会到我的适配器类。它需要显示添加到数组列表中的数据，但是它没有，数组列表的大小总是0。

我的recyclerview类是forecast

oncreate

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_forecast);
Intent intent = getIntent();
Latitude = intent.getDoubleExtra("lat",0);
Longitude = intent.getDoubleExtra("long",0);
System.out.println("LATİTUDE "+Latitude+" Longitude "+Longitude);//i just experimented to 
   check if latitude and 
   longitude come
init();
}

init ()

public void init(){
arrayList = new ArrayList<>();
forecast_back_icon = findViewById(R.id.forecast_back_icon);
recyclerviewforecast = findViewById(R.id.RecyclerviewForecast);

get_forecast_data(Latitude,Longitude);

forecastAdapter = new ForecastAdapter(arrayList);
recyclerviewforecast.setAdapter(forecastAdapter);
recyclerviewforecast.setLayoutManager(new LinearLayoutManager(forecast.this));
forecast_back_icon();
}

get_forecast_data()功能

public void get_forecast_data(Double Lat, Double Long){
//EXAMPLE URL
//https://api.openweathermap.org/data/2.5/weather?lat={lat}&lon={lon}&appid={API%20key}

API_KEY_FORECAST = "c29ecfafd4a70caad8fee38d6054bfc7";
URL_FORECAST = "https://api.openweathermap.org/data/2.5/onecall?lat="+Lat+"&lon="+Long+"&exclude=current,minutely,hourly,alerts&appid="+API_KEY_FORECAST;
RequestQueue queue = Volley.newRequestQueue(getApplicationContext());
JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, URL_FORECAST, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
JSONArray daily = response.getJSONArray("daily");
for(int i=0;i<daily.length();i++){
String  temp = daily.getJSONObject(i).getJSONObject("temp").getString("day");
String feels_like = daily.getJSONObject(i).getJSONObject("feels_like").getString("day");
String pressure = daily.getJSONObject(i).getString("pressure");
String humidity = daily.getJSONObject(i).getString("humidity");
String wind_speed = daily.getJSONObject(i).getString("wind_speed");
String icon = daily.getJSONObject(i).getJSONArray("weather").getJSONObject(0).getString("icon");
String description = daily.getJSONObject(i).getJSONArray("weather").getJSONObject(0).getString("description");
arrayList.add(new RecyclerviewModel(temp,humidity,feels_like,pressure,description,wind_speed,icon));
}
}
catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
error.printStackTrace();
}
});
queue.add(request);
System.out.println("forecast class arraylist size : --> "+arrayList.size());
}

当我在底部检查时，数组列表的大小为0

my forecast adapter class

public class ForecastAdapter extends RecyclerView.Adapter<ForecastAdapter.MyForecastViewHolder> {
ArrayList<RecyclerviewModel> ForecastArraylist;

public ForecastAdapter(ArrayList<RecyclerviewModel> ForecastArraylist){
this.ForecastArraylist = ForecastArraylist;
System.out.println("ForecastAdapter arraylist size : --- > "+ForecastArraylist.size());
}
@NonNull
@Override
public MyForecastViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
RecyclerviewForecastRowBinding recyclerviewForecastRowBinding = RecyclerviewForecastRowBinding.inflate(LayoutInflater.from(parent.getContext()),parent,false);
return new MyForecastViewHolder(recyclerviewForecastRowBinding);
}
@Override
public void onBindViewHolder(@NonNull MyForecastViewHolder holder, int position) {

System.out.println("we are in onbindviewholder.... ");
Double temperature = Double.parseDouble(ForecastArraylist.get(position).getTemperature()) - 273.15;
System.out.println(temperature);
Double feels_like = Double.parseDouble(ForecastArraylist.get(position).getFeels_like()) - 273.15;

holder.binding.txtRecyclerviewTemp.setText(temperature.toString().substring(0,4)+"°");
holder.binding.txtRecyclerviewFeelslike.setText(feels_like.toString().substring(0,4)+"°");
holder.binding.txtRecyclerviewHumidity.setText("%"+ForecastArraylist.get(position).getHumadity());
holder.binding.txtRecyclerviewPressure.setText(ForecastArraylist.get(position).getPressure()+"hPa");
holder.binding.txtRecyclerviewWindSpeed.setText(ForecastArraylist.get(position).getWind_speed()+"km/h");
holder.binding.txtRecyclerviewCloud.setText(ForecastArraylist.get(position).getDescription());
String icon_id = ForecastArraylist.get(position).getId();
load_weather_icon(icon_id,holder);

}
@Override
public int getItemCount() {
return ForecastArraylist.size();
}
public class MyForecastViewHolder extends RecyclerView.ViewHolder{
private RecyclerviewForecastRowBinding binding;
public MyForecastViewHolder(@NonNull RecyclerviewForecastRowBinding binding) {
super(binding.getRoot());
this.binding = binding;
}
}
public void load_weather_icon(String id,MyForecastViewHolder holder ){
int id1 = Integer.valueOf(id);
if(id1>=200 && id1 <= 232){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.thunderstorm);
}
else if(id1>=300 && id1<= 321){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.showerrain);
}
else if(id1>=500 && id1<= 504){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.rain);
}
else if(id1 == 511){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.snow);
}
else if(id1>=520 && id1<= 531){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.showerrain);
}
else if(id1>=600 && id1<= 622){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.snow);
}
else if(id1>=701 && id1<= 781){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.mist);
}
else if(id1 == 800 ){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.clearsky);
}
else if(id1 == 801){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.fewclouds);
}
else if(id1 == 802){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.scatteredclouds);
}
else if(id1 == 803){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.brokenclouds);
}
else if(id1 == 804){
holder.binding.recyclerviewCloudImg.setBackgroundResource(R.drawable.brokenclouds);
}
}

}

我在预测适配器中看不到'we are in onbindviewholder'

xml预测

<LinearLayout
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"
xmlns:app="http://schemas.android.com/apk/res-auto"
tools:context=".forecast"
android:orientation="vertical"
android:id="@+id/forecastLayout">
<com.google.android.material.appbar.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:id="@+id/Toolbarcities">
<androidx.constraintlayout.widget.ConstraintLayout
android:id="@+id/toolbarconstraintforecast"
android:layout_width="match_parent"
android:layout_height="?actionBarSize"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">

<androidx.appcompat.widget.Toolbar
android:id="@+id/MyToolbarforecast"
android:layout_width="match_parent"
android:layout_height="?actionBarSize"
android:background="?attr/colorPrimary"
android:minHeight="?attr/actionBarSize"
android:theme="?attr/actionBarTheme"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:titleTextColor="@color/white"
>
<ImageView
android:id="@+id/forecast_back_icon"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/cities_back_icon"
></ImageView>
</androidx.appcompat.widget.Toolbar>
</androidx.constraintlayout.widget.ConstraintLayout>
</com.google.android.material.appbar.AppBarLayout>
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/RecyclerviewForecast"
android:layout_width="match_parent"
android:layout_height="match_parent" />

Answer 1

这里的问题是，在处理Volley请求和填充数组列表之前，您已经创建了带有空数组列表的适配器，并将其分配给Recyclerview。有两种方法可以解决这个问题。首先是创建适配器，并在Volley请求的OnResponse方法中设置适配器。或者，您可以在适配器中创建一个方法，用于更新数组列表并通知适配器数据集已更改。我希望你能理解。

第一个是最简单的