java - 在类之间传递值以及更新回收器 View 时如何修复 "System services not available to Activities before onCreate"？

Question

我正在制作接受收银应用程序的订单。使用回收器 View 显示订单队列。但是，我在类之间传递 ArrayList 值以及更新回收器 View 时遇到问题。在这种情况下，我不会有大量的回收器 View ，因此性能不会成为太大的问题，但我们将非常赞赏执行此操作的优化方法。我只是不知道如何解决这个问题。

我尝试在 MainActivty 类中创建一个 set 方法，我也尝试过 put extra 的 Intent ，但我不认为我完全理解 put extra 。

主要 Activity 类:

public class MainActivity extends AppCompatActivity implements MyRecyclerViewAdapter.ItemClickListener {
    private RecyclerView recyclerView;
    private RecyclerView.Adapter mAdapter;
    private RecyclerView.LayoutManager layoutManager;
    public  ArrayList<String> orderList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        // set up the RecyclerView
        recyclerView = findViewById(R.id.recyle_view_activity);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        mAdapter = new MyRecyclerViewAdapter(this, orderList);
        ((MyRecyclerViewAdapter) mAdapter).setClickListener(this);


        recyclerView.addItemDecoration(new DividerItemDecoration(this,
                DividerItemDecoration.VERTICAL));


        recyclerView.setAdapter(mAdapter);


    }

    //This is the set method I attempted:
    public void setOrderAdd(ArrayList<String> data){
        if (data != null){
           mAdapter = new MyRecyclerViewAdapter(this,data); //Error refrences here
        }
    }
}

其他类:

public class regularCoffee extends AppCompatActivity implements AdapterView.OnItemSelectedListener, Serializable {
   protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_regular_coffee);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        addToOrder();

}

public void addToOrder(){
        //Reg Addons:
        final CheckBox leaveRoomReg = findViewById(R.id.leave_room_reg);
        final CheckBox cinnamonReg = findViewById(R.id.cinnamon_reg);
        final CheckBox chocolateSyrupReg = findViewById(R.id.chocolate_syrup_reg);
        final CheckBox whiteChocolateSyrupReg = findViewById(R.id.white_chocolate_syrup_reg);
        final CheckBox caramelReg = findViewById(R.id.caramelReg);
        final CheckBox hazelnutReg = findViewById(R.id.hazel_nut_reg);

        final CheckBox[] RegCoffeeAddOns = {leaveRoomReg,cinnamonReg,chocolateSyrupReg,whiteChocolateSyrupReg,caramelReg,hazelnutReg};

        //Decaf Addons:
        final Button leaveRoomDecaf = findViewById(R.id.leave_room_decaf);
        final Button cinnamonDecaf = findViewById(R.id.cinnamon_decaf);
        final Button chocolateSyrupDecaf = findViewById(R.id.chocolate_syrup_decaf);
        final Button whiteChocolateDecaf = findViewById(R.id.white_chocolate_syrup_decaf);
        final Button caramelDecaf = findViewById(R.id.caramel_decaf);
        final Button hazelnutDecaf = findViewById(R.id.hazel_nut_decaf);

        final Button[] DecafCoffeeAddOns = {leaveRoomDecaf,cinnamonDecaf,caramelDecaf,chocolateSyrupDecaf,whiteChocolateDecaf,hazelnutDecaf};

        Button addToOrderButton = findViewById(R.id.addToOrderReg);



        addToOrderButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                MainActivity addToOrderArea = new MainActivity();
                String forOrder;
                ArrayList<String> tempArray = new ArrayList<>();

                if (regCoffeeQuantity > 0){
                    forOrder = "Regular Coffee (x" + regCoffeeQuantity + ") \n   ";
                    for (int i = 0; i < RegCoffeeAddOns.length; i++){
                        if (RegCoffeeAddOns[i].isChecked()){
                            forOrder = forOrder + "| " + RegCoffeeAddOns[i].getText().toString() + " ";
                            System.out.println(forOrder);
                        }
                    }

                   addToOrderArea.setOrderAdd(tempArray); //Error refrences here

                }
            }
        });
    }

RecyclerView适配器:

package com.example.holygroundsapplication;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.ViewHolder> {

    private List<String> mData;
    private LayoutInflater mInflater;
    private ItemClickListener mClickListener;

    // data is passed into the constructor
    MyRecyclerViewAdapter(Context context, List<String> data) {
        this.mInflater = LayoutInflater.from(context); //Error refrences here.
        this.mData = data;
    }


    // inflates the row layout from xml when needed
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = mInflater.inflate(R.layout.recyclerview_row, parent, false);
        return new ViewHolder(view);

    }

    // binds the data to the TextView in each row
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        String animal = mData.get(position);
        holder.myTextView.setText(animal);
    }

    // total number of rows
    @Override
    public int getItemCount() {
        return mData.size();
    }


    // stores and recycles views as they are scrolled off screen
    public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
        TextView myTextView;

        ViewHolder(View itemView) {
            super(itemView);
            myTextView = itemView.findViewById(R.id.tvAnimalName);
            itemView.setOnClickListener(this);
        }

        @Override
        public void onClick(View view) {
            if (mClickListener != null) mClickListener.onItemClick(view, getAdapterPosition());
        }
    }

    // convenience method for getting data at click position
    String getItem(int id) {
        return mData.get(id);
    }

    // allows clicks events to be caught
    void setClickListener(MainActivity itemClickListener) {
        this.mClickListener = itemClickListener;
    }

    // parent activity will implement this method to respond to click events
    public interface ItemClickListener {
        void onItemClick(View view, int position);
    }
}

这是错误:

 java.lang.IllegalStateException: System services not available to Activities before onCreate()
        at android.app.Activity.getSystemService(Activity.java:5774)
        at android.view.LayoutInflater.from(LayoutInflater.java:233)
        at com.example.holygroundsapplication.MyRecyclerViewAdapter.<init>(MyRecyclerViewAdapter.java:21)
        at com.example.holygroundsapplication.MainActivity.setOrderAdd(MainActivity.java:89)
        at com.example.holygroundsapplication.regularCoffee$8.onClick(regularCoffee.java:262)
...

Answer 1

在您的 onClick 函数中，您有

MainActivity addToOrderArea = new MainActivity();

您不应自行创建 Activity 实例。这是Android系统所做的事情。因为您自己创建了 Activity，所以它没有被初始化(即 onCreate() 没有被调用)。 setOrderAdd() 中创建的适配器需要初始化 Activity，因此会引发异常。

为了防止这些问题，您需要使用 startActivity() 创建 Activity。您可以通过向起始 Intent 添加额外内容来将数据传递到新 Activity。