求助：ViewPager中3个ListFragment内容无法显示问题

我开发了一个带有ViewPager的Android应用，需要展示4个标签页，其中3个为ListFragment。但运行应用时，这3个ListFragment显示为空。以下是我的相关代码：

MainActivity.java #

package com.hwdeveloper.bitsandpizzas; 
import android.content.Context; 
import android.content.Intent; 
import android.support.annotation.NonNull; 
import android.support.annotation.Nullable; 
import android.support.design.widget.TabLayout; 
import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.app.FragmentPagerAdapter; 
import android.support.v4.view.MenuItemCompat; 
import android.support.v4.view.PagerAdapter; 
import android.support.v4.view.ViewPager; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.support.v7.widget.ShareActionProvider; 
import android.support.v7.widget.Toolbar; 
import android.util.AttributeSet; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 

public class MainActivity extends AppCompatActivity { 
    private ShareActionProvider shareActionProvider; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.activity_main); 
        Toolbar toolbar = findViewById(R.id.toolbar); 
        setSupportActionBar(toolbar); 
        SectionsPagerAdapter pagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 
        ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager); 
        viewPager.setAdapter(pagerAdapter); 
        TabLayout tabLayout = (TabLayout)findViewById(R.id.tabs); 
        tabLayout.setupWithViewPager(viewPager); 
    } 

    @Override 
    public View onCreateView(String name, Context context, AttributeSet attrs) { 
        return super.onCreateView(name, context, attrs); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
        getMenuInflater().inflate(R.menu.menu_main, menu); 
        MenuItem menuItem = menu.findItem(R.id.action_share); 
        shareActionProvider = (ShareActionProvider) MenuItemCompat.getActionProvider(menuItem); 
        setShareActionProvider("Want join me for Pizza?"); 
        return super.onCreateOptionsMenu(menu); 
    } 

    public void setShareActionProvider(String text) { 
        Intent intent = new Intent(Intent.ACTION_SEND); 
        intent.setType("Text/Plain"); 
        intent.putExtra(Intent.EXTRA_TEXT, text); 
        shareActionProvider.setShareIntent(intent); 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
        switch (item.getItemId()) { 
            case R.id.action_create_order: 
                Intent intent = new Intent(this, OrderActivity.class); 
                startActivity(intent); 
                return true; 
            default: 
                return super.onOptionsItemSelected(item); 
        } 
    } 
} 

SectionsPagerAdapter.java #

public class SectionsPagerAdapter extends FragmentPagerAdapter { 
    SectionsPagerAdapter(FragmentManager fm) { 
        super(fm); 
    } 

    @Override 
    public int getCount() { 
        return 4; 
    } 

    @Override 
    public int getItemPosition(@NonNull Object object) { 
        return PagerAdapter.POSITION_NONE; 
    } 

    @Nullable 
    @Override 
    public CharSequence getPageTitle(int position) { 
        switch (position){ 
            case 0: return "Home"; 
            case 1: return "Pizza"; 
            case 2: return "Pasta"; 
            case 3: return "Stores"; 
        } 
        return super.getPageTitle(position); 
    } 

    @Override 
    public Fragment getItem(int position) { 
        switch (position) { 
            case 0: return new TopFragment(); 
            case 1: return new PizzaFragment(); 
            case 2: return new PastaFragment(); 
            case 3: return new StoresFragment(); 
            default: return null; 
        } 
    } 
} 

TopFragment.java #

public class TopFragment extends Fragment { 
    public TopFragment() { 
        // Required empty public constructor 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
        // Inflate the layout for this fragment 
        return inflater.inflate(R.layout.fragment_top, container, false); 
    } 
} 

PizzaFragment.java #

public class PizzaFragment extends ListFragment { 
    public PizzaFragment() { 
        // Required empty public constructor 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
        ArrayAdapter<String> adapter = new ArrayAdapter<>(inflater.getContext(),android.R.layout.simple_list_item_1, getResources().getStringArray(R.array.pizzas)); 
        setListAdapter(adapter); 
        return super.onCreateView(inflater, container, savedInstanceState); 
    } 
} 

PastaFragment.java #

public class PastaFragment extends ListFragment { 
    public PastaFragment() { 
        // Required empty public constructor 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
        ArrayAdapter<String> adapter = new ArrayAdapter<>(inflater.getContext(), android.R.layout.simple_list_item_1,getResources().getStringArray(R.array.pasta)); 
        setListAdapter(adapter); 
        return super.onCreateView(inflater, container, savedInstanceState); 
    } 
} 

StoresFragment（代码不完整） #

问题排查与修复方案 #

我帮你看了下代码，ListFragment显示为空主要是因为适配器初始化的时机不对，还有几个细节需要确认，具体修复步骤如下：

1. 调整ListFragment的适配器初始化位置 #

onCreateView方法是用来创建Fragment视图的，此时ListView还没完全绑定到Fragment的生命周期里，直接在这里调用setListAdapter大概率不会生效。正确的做法是把适配器的初始化代码移到onActivityCreated方法中——这个方法会在Fragment成功附加到Activity、视图层级完全创建后执行，此时设置适配器才能确保ListView能正确接收数据。

修改PizzaFragment.java：

public class PizzaFragment extends ListFragment { 
    public PizzaFragment() { 
        // Required empty public constructor 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
        // 直接返回ListFragment的默认视图即可
        return super.onCreateView(inflater, container, savedInstanceState); 
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        // 在这里初始化并设置适配器
        ArrayAdapter<String> adapter = new ArrayAdapter<>(getActivity(), 
                android.R.layout.simple_list_item_1, 
                getResources().getStringArray(R.array.pizzas)); 
        setListAdapter(adapter);
    }
}

同样的，把PastaFragment.java改成下面这样：

public class PastaFragment extends ListFragment { 
    public PastaFragment() { 
        // Required empty public constructor 
    } 

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

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        ArrayAdapter<String> adapter = new ArrayAdapter<>(getActivity(), 
                android.R.layout.simple_list_item_1, 
                getResources().getStringArray(R.array.pasta)); 
        setListAdapter(adapter);
    }
}

2. 确认字符串数组资源存在 #

检查你项目里的res/values/strings.xml文件，确保已经正确定义了pizzas和pasta这两个字符串数组，示例如下：

<string-array name="pizzas">
    <item>玛格丽特披萨</item>
    <item>意大利辣香肠披萨</item>
    <item>夏威夷披萨</item>
</string-array>

<string-array name="pasta">
    <item>培根蛋酱意面</item>
    <item>阿尔弗雷多奶油意面</item>
    <item>香辣通心粉</item>
</string-array>

如果这些数组不存在，getResources().getStringArray()会返回null，适配器没有数据，列表自然就显示为空了。

3. 完善StoresFragment的实现 #

因为你提到StoresFragment代码不完整，如果它也是ListFragment的话，按照上面的方式完成初始化逻辑即可——确保在onActivityCreated里设置适配器和数据。

做完这些修改后，重新运行应用，你的三个ListFragment应该就能正常显示数据了。

内容的提问来源于stack exchange，提问作者it4Astuces