我想从 Activity 获取编辑文本数据并显示在 Fragment 中，但它给了我错误

Question

I want to get Edit Text data from activity and use it in fragment. Basically in Fragment I show the current weather data with city name which I entered and I entered this Edit text data in Main Activity and pass this Edit Text data in fragment and set this string value in fragment.

So I have these errors. I try a lot to solve it but I can not resolve it.

MainActivity.Class

package com.deitel.apiretrofitfragmentweatherapp;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentManager;
import androidx.viewpager.widget.ViewPager;

import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.Toast;

import com.deitel.apiretrofitfragmentweatherapp.Adapter.FragementViewAdapter;
import com.deitel.apiretrofitfragmentweatherapp.Fragment.ForcastWeather;
import com.deitel.apiretrofitfragmentweatherapp.Fragment.currentweather;
import com.google.android.material.tabs.TabLayout;

public class MainActivity extends AppCompatActivity {
    private  static FragmentManager fragmentManager;
    public static String BaseUrl = "http://api.openweathermap.org/";
    public static String AppId = "08fd7374790f2ccee9f1f1dbfae38fdf";
    ViewPager viewPager;
    FragementViewAdapter fragementViewAdapter;
    TabLayout tabLayout;
    EditText text_search;
    ImageButton btn_search;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        fragmentManager=getSupportFragmentManager();
        text_search = findViewById(R.id.text_search_city);
        tabLayout = findViewById(R.id.tab_layout);
        viewPager = findViewById(R.id.fragment_container);
        btn_search = findViewById(R.id.btn_search);
        final String City = text_search.getText().toString().trim();
        btn_search.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Bundle bundle = new Bundle();
                bundle.putString("search_city",City);
                currentweather currentweather = new currentweather();
                currentweather.setArguments(bundle);
                fragmentManager.beginTransaction().replace(R.id.fragment_container,currentweather).commit();
                Toast.makeText(MainActivity.this, "successfully", Toast.LENGTH_SHORT).show();
            }
        });
        fragementViewAdapter = new FragementViewAdapter(getSupportFragmentManager());
        viewPager.setAdapter(fragementViewAdapter);
        tabLayout.setupWithViewPager(viewPager);
        fragmentManager=getSupportFragmentManager();
  }
}

CurrentWeatherFragment.Class

package com.deitel.apiretrofitfragmentweatherapp.Fragment;

import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.text.TextUtils;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;

import com.deitel.apiretrofitfragmentweatherapp.CurrentWeather.WeatherResponse;
import com.deitel.apiretrofitfragmentweatherapp.ForecastWeather.City;
import com.deitel.apiretrofitfragmentweatherapp.R;
import com.deitel.apiretrofitfragmentweatherapp.Retrofit.WeatherService;

import java.text.SimpleDateFormat;
import java.util.Calendar;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

import static com.deitel.apiretrofitfragmentweatherapp.MainActivity.AppId;
import static com.deitel.apiretrofitfragmentweatherapp.MainActivity.BaseUrl;

public class currentweather extends Fragment {
    public TextView text_country,text_city,text_pressure,text_humidity,text_temp;
    public TextView textView_country, textView_city, textView_temp,
            textView_pressure, textView_humidity, textview_date;
    /*public TextView text_view;*/
    public currentweather() {
        // Required empty public constructor
    }
        @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
        View itemview=inflater.inflate(R.layout.fragment_currentweather, container, false);
            textView_country = itemview.findViewById(R.id.textView_country);
            textView_city =itemview.findViewById(R.id.textView_city);
            textView_temp =itemview.findViewById(R.id.textview_temp);
            textView_pressure =itemview.findViewById(R.id.textView_pressure);
            textView_humidity =itemview.findViewById(R.id.textView_humidity);
            textview_date =itemview.findViewById(R.id.textView_date);
            text_country= itemview.findViewById(R.id.text_country);
            text_city=itemview. findViewById(R.id.text_city);
            /*text_view=itemview.findViewById(R.id.text_view);*/
            text_pressure=itemview. findViewById(R.id.text_pressure);
            text_humidity=itemview.findViewById(R.id.text_humidity);
            text_temp=itemview.findViewById(R.id.text_temp);
            text_country.setVisibility(View.GONE);
            text_city.setVisibility(View.GONE);
            text_pressure.setVisibility(View.GONE);
            text_humidity.setVisibility(View.GONE);
            text_temp.setVisibility(View.GONE);
            getCurrentData();
            return itemview;
    }
    void getCurrentData() {
         String city=getArguments().getString("search_city");
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(BaseUrl)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
        WeatherService weatherService = retrofit.create(WeatherService.class);
        Call<WeatherResponse> call = weatherService.getCurrentWeatherDataCityName(city, AppId);
        call.enqueue(new Callback() {
            @Override
            public void onResponse(Call call, Response response) {
                if (response.code() == 200) {
                    WeatherResponse weatherResponse = (WeatherResponse) response.body();
                    assert weatherResponse != null;
                    Calendar calendar = Calendar.getInstance();
                    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EEEE-dd-MM");
                    String formatedate = simpleDateFormat.format(calendar.getTime());
                   /* String stringbuilder= "Country : " +
                            weatherResponse.sys.country +
                            "\n" +
                            "City : " +weatherResponse.name +
                            "\n" +
                            "Tempreture : " + weatherResponse.main.temp +
                            "\n" +
                            "Tempreture(Min) : " +
                            weatherResponse.main.temp_min +
                            "\n" +
                            "Tempreture(Max) : " +
                            weatherResponse.main.temp_max +
                            "\n" +
                            "Humidity : " +
                            weatherResponse.main.humidity +
                            "\n" +
                            "Pressure : " +
                            weatherResponse.main.pressure;*/
                    String Country = weatherResponse.sys.country;
                    String City = weatherResponse.name;
                    String Temp = String.valueOf(weatherResponse.main.temp);
                    Double calcius = Double.parseDouble(Temp) - 273.0;
                    Integer i = calcius.intValue();
                    String Pressure = String.valueOf(weatherResponse.main.pressure);
                    String Humidity = String.valueOf(weatherResponse.main.humidity);
                    textView_country.setText(Country);
                    textView_city.setText(City);
                    textView_temp.setText(String.valueOf(i));
                    textView_pressure.setText(Pressure);
                    textView_humidity.setText(Humidity);
                    textview_date.setText(formatedate);
                    text_country.setVisibility(View.VISIBLE);
                    text_city.setVisibility(View.VISIBLE);
                    text_pressure.setVisibility(View.VISIBLE);
                    text_humidity.setVisibility(View.VISIBLE);
                    text_temp.setVisibility(View.VISIBLE);
                }
                if (response.code()==404)
                {
                }
            }
            @Override
            public void onFailure(Call call, Throwable t) {
                textView_country.setText(t.getMessage());
                textView_city.setText(t.getMessage());
                textView_temp.setText(t.getMessage());
                textView_pressure.setText(t.getMessage());
                textView_humidity.setText(t.getMessage());
                textview_date.setText(t.getMessage());
            }
        });
    }

}

CurrentWeatherFragment.XML

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">
                        <TextView
                android:id="@+id/text_country"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="10dp"
                android:layout_marginLeft="10dp"
                android:layout_marginTop="10dp"
                android:text="Country"
                android:textColor="#000"
                android:textSize="25dp"
                android:textStyle="bold"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/textView_date" />

            <TextView
                android:id="@+id/textView_country"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="10dp"
                android:layout_marginLeft="10dp"
                android:layout_marginTop="10dp"
                android:text=""
                android:textColor="#000"
                android:textSize="17dp"
                android:textStyle="bold"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/text_country" />

            <TextView
                android:id="@+id/text_city"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:layout_marginEnd="10dp"
                android:layout_marginRight="10dp"
                android:text="City"
                android:textColor="#000"
                android:textSize="25dp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/textView_date" />

            <TextView
                android:id="@+id/textView_city"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:layout_marginEnd="10dp"
                android:layout_marginRight="10dp"
                android:text=""
                android:textColor="#000"
                android:textSize="17dp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/text_city" />

            <TextView
                android:id="@+id/text_temp"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="90dp"
                android:text="Temperature"
                android:textColor="#000"
                android:textSize="25dp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="@+id/textView_country"
                app:layout_constraintTop_toBottomOf="@id/textView_date" />

            <TextView
                android:id="@+id/textview_temp"
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:layout_marginTop="40dp"
                android:gravity="center"
                android:text=""
                android:textColor="#000"
                android:textSize="40dp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="@+id/text_temp" />

            <TextView
                android:id="@+id/text_pressure"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:text="Pressure"
                android:textColor="#000"
                android:textSize="25dp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/textview_temp" />

            <TextView
                android:id="@+id/textView_pressure"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:text=""
                android:textColor="#000"
                android:textSize="17dp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/text_pressure" />

            <TextView
                android:id="@+id/text_humidity"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:text="Humidity"
                android:textColor="#000"
                android:textSize="25dp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/textView_pressure" />

            <TextView
                android:id="@+id/textView_humidity"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="32dp"
                android:layout_marginBottom="32dp"
                android:text=""
                android:textColor="#000"
                android:textSize="17dp"
                android:textStyle="bold"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/text_humidity" />-->

            <TextView
                android:id="@+id/textView_date"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:text=""
                android:textColor="#000"
                android:textSize="17dp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parentpa" />

        </androidx.constraintlayout.widget.ConstraintLayout>
    </ScrollView>
</androidx.constraintlayout.widget.ConstraintLayout>

Errors:

    01-03 15:16:31.862 15251-15251/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.deitel.apiretrofitfragmentweatherapp, PID: 15251
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on
a null object reference
        at com.deitel.apiretrofitfragmentweatherapp.Fragment.currentweather.getCurrentData(currentweather.java:69)
        at com.deitel.apiretrofitfragmentweatherapp.Fragment.currentweather.onCreateView(currentweather.java:64)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2600)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881)
        at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
        at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
        at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
        at androidx.fragment.app.FragmentManagerImpl.execSingleAction(FragmentManagerImpl.java:1696)
        at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:299)
        at androidx.fragment.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:235)

Answer 1

As I understand from your question, You have one Activity class and a fragment is inside that activity. You have one edit text for search in your activity class and When you enter something in your activity's search box you want that result in your fragment class. If I understood your requirement then you should change a bit your current implementation.

1. Create a class level (Global) fragment instance.
2. Create one method with string input parameter (eg. searchWeather(String searchedText)) in fragment and make it public.
3. After Text input completed you just call fragment's method from activity class as we have a present current object of that fragment in screen(ex. currentweather.searchWeather("test") )
4. Now you might get that last entered text in your fragment.

This way you can manage communication between activity and fragment.

Please feel free to ask, If you have any further issues/questions in implementation.

Example :

Activity class:

public class MainActivity extends Activity {

CurrentWeatherFragment currentWeatherFragment;
EditText searchText;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    searchText = new EditText(this);

    currentWeatherFragment = new CurrentWeatherFragment();
    getFragmentManager().beginTransaction().replace(R.id.fragment_container,currentWeatherFragment).commit();

    searchText.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {

        }

        @Override
        public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
                 if (currentWeatherFragment != null){
                     currentWeatherFragment.searchWeather(charSequence.toString());
                 }
        }

        @Override
        public void afterTextChanged(Editable editable) {

        }
    });

}
}

Fragment class:

public class CurrentWeatherFragment extends Fragment {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    return super.onCreateView(inflater, container, savedInstanceState);
}

public void searchWeather(String searchedText){
    //Do your work here
    }
}

Answer 2

I see that you need the city name which you enter in your MainActivity when you make Retrofit call to fetch the weather data from your fragment class. So your city data should not be empty or null.

I see that you are getting the text using the line final String City = text_search.getText().toString().trim(); in your MainActivity. Kindly put that line onside the click listener of button like below

 btn_search.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String City = text_search.getText().toString().trim();
            Bundle bundle = new Bundle();
            bundle.putString("search_city",City);
            currentweather currentweather = new currentweather();
            currentweather.setArguments(bundle);
            fragmentManager.beginTransaction().replace(R.id.fragment_container,currentweather).commit();
            Toast.makeText(MainActivity.this, "successfully", Toast.LENGTH_SHORT).show();
        }
    });

This will get the text from the edittext whenever you click on search button and you will not receive the null exception.