如何通过SumCost方法为RecyclerView的textCost TextView设置文本？

我创建了一个RecyclerView适配器，添加新条目时需要为两个TextView设置文本。其中id为text的TextView设置文本没有问题，请问如何通过以下SumCost方法为id为textCost的TextView设置文本？

private double SumCost(String result){
    switch (result){
        case "4820049490145":
            return 2.34;
        default: return 0;
    }
}

String类型的result是从ScanPage页面获取的，完整代码如下：

activity_scan_page.xml: #

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    android:padding="10dp">


    <TextView
        android:id="@+id/SumText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="0.00"
        android:textSize="30sp"/>
    <Button
        android:id="@+id/scanBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Scan now"
        android:textSize="30sp"
        android:layout_gravity="center_horizontal"/>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>


</LinearLayout>

item.xml: #

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_margin="10dp"
    app:cardCornerRadius="10dp"
    app:cardElevation="5dp"
    app:contentPadding="5dp">


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:text="@string/app_name"
            android:textSize="20sp" />

        <TextView
            android:id="@+id/textCost"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/text"
            android:text="@string/app_name"
            android:textSize="20sp" />

        <Button
            android:id="@+id/delete"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_alignParentEnd="true"
            android:layout_marginTop="3dp"
            android:layout_marginEnd="3dp"
            android:text="Delete" />
    </RelativeLayout>

</androidx.cardview.widget.CardView>

ScanPage.java（在此获取IntentResult result，并通过items.add(result)设置android:id="@+id/text"）: #

package com.example.scanapp;

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

import android.app.ActionBar;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.google.zxing.integration.android.IntentIntegrator;
import com.google.zxing.integration.android.IntentResult;

import java.util.LinkedList;
import java.util.List;

public class ScanPage extends AppCompatActivity implements View.OnClickListener{


    Button scanBtn;
    TextView editText;

    List<String> items = new LinkedList<>();


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



        scanBtn = findViewById(R.id.scanBtn);
        scanBtn.setOnClickListener(this);

    }
    public void AddItem(String result){
        RecyclerView recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        DemoAdapter adapter = new DemoAdapter(items);
        recyclerView.setAdapter(adapter);

        items.add(result);

    }


    @Override
    public void onClick(View view) {
        scanCode();
    }

    private  void scanCode(){
        IntentIntegrator integrator = new IntentIntegrator(this);
        integrator.setCaptureActivity(CaptureAct.class);
        integrator.setOrientationLocked(false);
        integrator.setDesiredBarcodeFormats(IntentIntegrator.ALL_CODE_TYPES);
        integrator.setPrompt("Scanning code");
        integrator.initiateScan();
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data){
        IntentResult result = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
        if(result != null){
            if(result.getContents() != null){
                AlertDialog.Builder builder = new AlertDialog.Builder(this);
                builder.setMessage(result.getContents());
                builder.setTitle("Scanning Result");
                builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        dialogInterface.cancel();

                        ///
                        AddItem(result.getContents());
                        ///

                        editText = (TextView) findViewById(R.id.SumText);
                        editText.setText(Cost(SumCost(result.getContents())));
                    }
                });
                AlertDialog dialog = builder.create();
                dialog.show();
            }
            else {
                Toast.makeText(this,"No result", Toast.LENGTH_LONG).show();
            }
        }
        else {
            super.onActivityResult(requestCode, resultCode, data);
        }
    }
    ////////

    double SumVar = 0;


    private double SumCost(String result){
        switch (result){
            case "4820049490145":
                return 2.34;
            default: return 0;
        }
    }
    private String Cost(double cost){
        SumVar += cost;
        return Double.toString(SumVar);
    }
    ////////
}

DemoAdapter.java: #

package com.example.scanapp;

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

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class DemoAdapter extends RecyclerView.Adapter<DemoVH>{

    List<String> items;

   

    public DemoAdapter(List<String> items){
        this.items = items;
    }

    @NonNull
    @Override
    public DemoVH onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item, parent, false);
        return new DemoVH(view).linkAdapter(this);
    }

    @Override
    public void onBindViewHolder(@NonNull DemoVH holder, int position) {
        holder.textView.setText(items.get(position));
    }

    @Override
    public int getItemCount() {
        return items.size();
    }
}

class DemoVH extends RecyclerView.ViewHolder{

    TextView textView;

    private DemoAdapter adapter;

    public DemoVH(@NonNull View itemView) {
        super(itemView);

        textView = itemView.findViewById(R.id.text);

        itemView.findViewById(R.id.delete).setOnClickListener(view -> {
            adapter.items.remove(getAdapterPosition());
            adapter.notifyItemRemoved(getAdapterPosition());
        });
    }
    public DemoVH linkAdapter(DemoAdapter adapter){
        this.adapter = adapter;
        return this;
    }
}

解决方案 #

按以下步骤修改代码即可实现需求：

1. 更新ViewHolder，添加textCost的引用

在DemoVH类中，新增对textCost TextView的绑定：

class DemoVH extends RecyclerView.ViewHolder{
    TextView textView;
    TextView textCostView; // 新增引用

    private DemoAdapter adapter;

    public DemoVH(@NonNull View itemView) {
        super(itemView);
        textView = itemView.findViewById(R.id.text);
        textCostView = itemView.findViewById(R.id.textCost); // 初始化textCost控件

        itemView.findViewById(R.id.delete).setOnClickListener(view -> {
            adapter.items.remove(getAdapterPosition());
            adapter.notifyItemRemoved(getAdapterPosition());
        });
    }

    public DemoVH linkAdapter(DemoAdapter adapter){
        this.adapter = adapter;
        return this;
    }
}

2. 在Adapter中实现SumCost方法并绑定文本

把ScanPage中的SumCost方法复制到DemoAdapter中，然后在onBindViewHolder里计算并设置textCost的文本：

public class DemoAdapter extends RecyclerView.Adapter<DemoVH>{
    List<String> items;

    public DemoAdapter(List<String> items){
        this.items = items;
    }

    // 新增SumCost方法，与ScanPage中的逻辑一致
    private double SumCost(String result){
        switch (result){
            case "4820049490145":
                return 2.34;
            default: return 0;
        }
    }

    @NonNull
    @Override
    public DemoVH onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item, parent, false);
        return new DemoVH(view).linkAdapter(this);
    }

    @Override
    public void onBindViewHolder(@NonNull DemoVH holder, int position) {
        String result = items.get(position);
        holder.textView.setText(result);
        // 计算金额并设置，格式化为两位小数提升显示效果
        double cost = SumCost(result);
        holder.textCostView.setText(String.format("%.2f", cost));
    }

    @Override
    public int getItemCount() {
        return items.size();
    }
}

3. 修复AddItem方法的性能问题

当前AddItem每次添加条目都会重新创建LayoutManager和Adapter，会造成不必要的性能损耗，修改为只初始化一次：
在ScanPage的onCreate方法中初始化RecyclerView：

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

    scanBtn = findViewById(R.id.scanBtn);
    scanBtn.setOnClickListener(this);

    // 初始化RecyclerView，仅执行一次
    RecyclerView recyclerView = findViewById(R.id.recyclerView);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    DemoAdapter adapter = new DemoAdapter(items);
    recyclerView.setAdapter(adapter);
}

然后修改AddItem方法，仅更新数据并通知适配器：

public void AddItem(String result){
    items.add(result);
    // 获取已初始化的适配器，通知新条目插入
    RecyclerView recyclerView = findViewById(R.id.recyclerView);
    DemoAdapter adapter = (DemoAdapter) recyclerView.getAdapter();
    adapter.notifyItemInserted(items.size() - 1);
}

修改完成后，每次扫描添加条目时，textCost就会根据SumCost方法返回的金额显示对应内容。

内容的提问来源于stack exchange，提问作者Ribter