将字符串从活动传递到片段

Question

您好我一直在研究问题并找到了将字符串从活动（不是片段活动）传递到片段的解决方案。 我想通过点击从 RestaurantsList.class 到 Mainsfragment.class 的文档 ID，在我的 onclick 中。

我得到的错误信息如下：

尝试在 null object 参考上调用虚拟方法 'android.content.Intent android.app.Activity.getIntent()'

这是我的活动代码：

package com.example.hostapp;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.RelativeLayout;

import com.example.hostapp.Adapters.RestaurantAdapter;
import com.example.hostapp.Adapters.categoryCardAdapter;
import com.example.hostapp.MenuFragments.MainsFragment;
import com.example.hostapp.Models.Restaurant;
import com.example.hostapp.Models.categoryCard;
import com.firebase.ui.firestore.FirestoreRecyclerOptions;
import com.google.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.Query;

public class RestaurantList extends AppCompatActivity {

    private FirebaseFirestore db = FirebaseFirestore.getInstance();
    private CollectionReference restaurantref = db.collection("restaurants");
    private RestaurantAdapter adapter;

    String categoryid = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_restaurant_list);


        setUpRecyclerView();
    }

    private void setUpRecyclerView() {


        //Get intent
        if (getIntent() != null)
            categoryid = getIntent().getStringExtra("categoryid");
        if (!categoryid.isEmpty() && categoryid != null) {
            Query query = restaurantref.whereEqualTo("categoryid", categoryid).orderBy("name");

            final FirestoreRecyclerOptions<Restaurant> options = new FirestoreRecyclerOptions.Builder<Restaurant>().setQuery(query, Restaurant.class).build();

            adapter = new RestaurantAdapter(options);

            RecyclerView recyclerView = findViewById(R.id.restaurant_recycler);
            recyclerView.setHasFixedSize(true);
            recyclerView.setLayoutManager(new LinearLayoutManager(this));
            recyclerView.setAdapter(adapter);

            adapter.setOnItemClickListerner(new RestaurantAdapter.OnItemClickListener() {
                @Override
                public void onItemClick(DocumentSnapshot documentSnapshot, int position) {
                    Restaurant restaurant = documentSnapshot.toObject(Restaurant.class);
                    Intent foodlist = new Intent(RestaurantList.this, Foodlist.class);


                    Bundle bundle = new Bundle();
                    bundle.putString("restaurantid", documentSnapshot.getId());
                    MainsFragment m4 = new MainsFragment();
                    m4.setArguments(bundle);


                    //foodlist.putExtra("restaurantid", documentSnapshot.getId());
                    startActivity(foodlist);


                }
            });
        }
    }


    @Override
    protected void onStart() {
        super.onStart();
        adapter.startListening();
    }

    @Override
    protected void onStop() {
        super.onStop();
        adapter.stopListening();
    }
}

这是我的片段代码：

package com.example.hostapp.MenuFragments;

import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.example.hostapp.Adapters.FoodAdapter;
import com.example.hostapp.Models.FoodModel;
import com.example.hostapp.R;
import com.example.hostapp.RestaurantList;
import com.firebase.ui.firestore.FirestoreRecyclerOptions;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.Query;


public class MainsFragment extends Fragment {


    private FirebaseFirestore db = FirebaseFirestore.getInstance();
    private FoodAdapter adapter;


    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_mains, container, false);

        String restaurantNumber = getArguments().getString("restaurantid");
        Query menuref = db.collectionGroup("Foods").whereEqualTo("menuid", restaurantNumber);

        FirestoreRecyclerOptions<FoodModel> options = new FirestoreRecyclerOptions.Builder<FoodModel>().
                setQuery(menuref, FoodModel.class)
                .build();

        adapter = new FoodAdapter(options);

        RecyclerView recyclerView = view.findViewById(R.id.recycler_mains);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this.getActivity()));
        recyclerView.setAdapter(adapter);


        return view;
    }

    private void setUpRecyclerView() {


    }

    @Override
    public void onStart() {
        super.onStart();
        adapter.startListening();
    }

    @Override
    public void onStop() {
        super.onStop();
        adapter.stopListening();
    }
}

Answer 1

我也有过这样的经历。 以下是我的处理方式：

1，通过intent.putExtra()将你的数据从RestaurantList活动传递到你的foodlist活动；

Intent foodlist = new Intent(RestaurantList.this, Foodlist.class);
foodlist.putExtra("restaurantid", documentSnapshot.getId());
startActivity(foodlist);

2、通过getIntent()从Foodlist活动中获取值；

String id = getIntent().getStringExtra("restaurantid");

3，将您的数据传递给您正在初始化适配器的适配器。 （像这样的东西：）

YourAdapter adapter = new YourAdapter(getSupportFragmentManager(), tabLayout.getTabCount(),id);

4，在适配器的构造函数中获取数据（您必须创建一个全局变量并将其填充到构造函数中）并在getItem（）方法中创建一个捆绑并将数据传递给它并将arguments设置为片段（如下面的代码）

public class YourAdapter extends FragmentStatePagerAdapter {
    int mNumOfTabs;
    String id;
    public AdapterPagerShift(FragmentManager fm, int NumOfTabs, String id) {
        super(fm);
        this.mNumOfTabs = NumOfTabs;
        this.id = id;
    }

    @Override
    public Fragment getItem(int position) {

        Bundle bundle = new Bundle();
        bundle.putString("restaurantid", documentSnapshot.getId());
        switch (position) {
            case 0:
                MainsFragment main = new MainsFragment();
                main.setArguments(bundle);
                return main;
            case 1:
                //...
            case 2:
               //...
            default:
                return null;
        }
    }

    @Override
    public int getCount() {
        return mNumOfTabs;
    }
}

5，在您的 MainsFragment class 中使用以下代码获取数据：

@Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        String id = getArguments().getString("restaurantid");

}

希望能帮助到你！