ArrayAdapter顯示錯誤：選項卡式活動和ListView

Question

我想創建一個包含列表的選項卡式活動。我創建了Tabbed Activity，我想在片段中創建列表。每個列表項目包含2個ImageViews和4個TextViews。因此，我創建了一個自定義類和一個自定義ArrayAdapter。這是代碼 -

1. Coins.java - 這是選項卡式活動的片段。

   package com.example.android.cotescol; 
   import android.os.Bundle; 
   import android.view.LayoutInflater; 
   import android.view.View; 
   import android.view.ViewGroup; 
   import android.widget.ListView; 
   import java.util.ArrayList; 
   public class Coins extends android.support.v4.app.Fragment{ 
       @Override 
       public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
        View rootView = inflater.inflate(R.layout.currency_list, container, false); 
   
        final ArrayList<CoinObject> coins = new ArrayList<Currency>(); 
   
        coins.add(new CoinObject(1, "India", 1947)); 
        coins.add(new CoinObject(1, "India", 1947)); 
   
        CoinAdapter itemsAdapter = new CoinAdapter(this, coins); 
        ListView listView = (ListView) findViewById(R.id.list); 
        listView.setAdapter(itemsAdapter); 
   
        return rootView; 
       } 
   } 
   

2. CoinObject.java - 這是一個自定義類，其中每個對象都包含硬幣的所有細節。

   package com.example.android.cotescol; 
   
   import java.util.HashMap; 
   import java.util.Locale; 
   import java.util.Map; 
   
   public class CoinObject { 
   
       private final static int NO_IMAGE_AVAILABLE = R.drawable.nia; 
       private final static String NOT_AVAILABLE = "Material Not Specified"; 
       private final static double NOT_KNOWN = 0.00; 
   
       private int denomination; 
       private String country; 
       private String countryCode; 
       private int year; 
       private int obverseImageResourceId = NO_IMAGE_AVAILABLE; 
       private int reverseImageResourceId = NO_IMAGE_AVAILABLE; 
       private String material = NOT_AVAILABLE; 
       private double diameter = NOT_KNOWN; 
       private double weight = NOT_KNOWN; 
       private double thickness = NOT_KNOWN; 
       private double value = NOT_KNOWN; 
   
       public CoinObject(int denomination, String country, int year, int obverseImageResourceId, int reverseImageResourceId , double diameter, double thickness, String material, double weight, double value) { 
        this.denomination = denomination; 
        this.country = country; 
        this.year = year; 
        this.obverseImageResourceId = obverseImageResourceId; 
        this.reverseImageResourceId = reverseImageResourceId; 
        this.diameter = diameter; 
        this.thickness = thickness; 
        this.material = material; 
        this.weight = weight; 
        this.value = value; 
        this.countryCode = getCountryCode(country); 
       } 
   
       public CoinObject(int denomination, String country, int year, double diameter, double thickness, String material, double weight, double value) { 
        this.denomination = denomination; 
        this.country = country; 
        this.year = year; 
        this.diameter = diameter; 
        this.thickness = thickness; 
        this.material = material; 
        this.weight = weight; 
        this.value = value; 
        this.countryCode = getCountryCode(country); 
       } 
   
       public CoinObject(int denomination, String country, int year) { 
        this.denomination = denomination; 
        this.country = country; 
        this.year = year; 
        this.countryCode = getCountryCode(country); 
       } 
   
       public String getCountryCode(String countryName) { 
        // Get all country codes in a string array. 
        String[] isoCountryCodes = Locale.getISOCountries(); 
        Map<String, String> countryMap = new HashMap<>(); 
        // Iterate through all country codes: 
        for (String code : isoCountryCodes) { 
         // Create a locale using each country code 
         Locale locale = new Locale("", code); 
         // Get country name for each code. 
         String name = locale.getDisplayCountry(); 
         // Map all country names and codes in key - value pairs. 
         countryMap.put(name, code); 
        } 
        // Get the country code for the given country name using the map. 
        // Here you will need some validation or better yet 
        // a list of countries to give to user to choose from. 
        String countryCode = countryMap.get(countryName); // "NL" for Netherlands. 
   
        return countryCode; 
       } 
   
       public int getDenomination() { return denomination; } 
       public int getYear() { return year; } 
       public int getObverseImageResourceId() { return obverseImageResourceId; } 
       public int getReverseImageResourceId() { return reverseImageResourceId; } 
       public double getDiameter() { return diameter; } 
       public double getWeight() { return weight; } 
       public double getThickness() { return thickness; } 
       public double getValue() { return value; } 
       public String getCountry() { return country; } 
       public String getCountryCode() { return countryCode; } 
       public String getMaterial() { return material; } 
   } 
   

3. CoinAdapter.java - 這是ArrayAdapter

   package com.example.android.cotescol; 
   
   import android.content.Context; 
   import android.support.annotation.NonNull; 
   import android.view.LayoutInflater; 
   import android.view.View; 
   import android.view.ViewGroup; 
   import android.widget.ArrayAdapter; 
   import android.widget.ImageView; 
   import android.widget.TextView; 
   
   import java.util.ArrayList; 
   
   public class CoinAdapter extends ArrayAdapter<CoinObject>{ 
       public CoinAdapter(Context context, ArrayList<CoinObject> currencies) { 
        super(context, 0, currencies); 
       } 
   
       @NonNull 
       @Override 
       public View getView(int position, View convertView, ViewGroup parent) { 
        View listItemView = convertView; 
        if (listItemView == null) { 
         listItemView = LayoutInflater.from(getContext()).inflate(R.layout.list_item, parent, false); 
        } 
   
        CoinObject currentCoinObject = getItem(position); 
   
        TextView denominationTextView = (TextView) listItemView.findViewById(R.id.denomination_text_view); 
        denominationTextView.setText(currentCoinObject.getDenomination()); 
   
        TextView countryTextView = (TextView) listItemView.findViewById(R.id.country_text_view); 
        countryTextView.setText(currentCoinObject.getCountry() + "(" + currentCoinObject.getCountryCode() + ")"); 
   
        TextView yearTextView = (TextView) listItemView.findViewById(R.id.year_text_view); 
        yearTextView.setText(currentCoinObject.getYear()); 
   
        ImageView obverseImageView = (ImageView) listItemView.findViewById(R.id.obverse_image_view); 
        obverseImageView.setImageResource(currentCoinObject.getObverseImageResourceId()); 
   
        ImageView reverseImageView = (ImageView) listItemView.findViewById(R.id.reverse_image_view); 
        reverseImageView.setImageResource(currentCoinObject.getReverseImageResourceId()); 
   
        return listItemView; 
       } 
   } 
   

在Coins.java文件的自定義，我在創建CoinAdapter類的實例得到一個錯誤。此外，findViewById（）以紅色顯示。 Error Picture

如果有人指導我以正確的方式做，這將是非常有益的。提前致謝。

Answer 1

替換：

CoinAdapter itemsAdapter = new CoinAdapter(this, coins); 

有了：

CoinAdapter itemsAdapter = new CoinAdapter(getActivity(), coins); 

替換：

ListView listView = (ListView) findViewById(R.id.list); 

有了：

ListView listView = (ListView) rootView.findViewById(R.id.list);