如何从xml资源中启动一个片段

Question

我有一个TabLayout活动，并且对于其中一个选项卡（情况3），我想将PreferenceFragment用于设置页面。在下面的情况3中，我已经声明了片段，但我该如何开始呢？

public static class SettingsFragment extends PreferenceFragment { 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     // Load the preferences from an XML resource 
     addPreferencesFromResource(R.xml.preferences); 
    } 

} 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View rootView = null; 
    switch (getArguments().getInt(ARG_SECTION_NUMBER)) { 
     case 1: { 
      rootView = inflater.inflate(R.layout.fragment_profile, container, false); 
      break; 
     } 
     case 2: { 
      rootView = inflater.inflate(R.layout.fragment_find, container, false); 
      break; 
     } 
     case 3: { 
      SettingsFragment fragment = new SettingsFragment(); 
      // what goes here? 
      break; 
     } 
    } 

    return rootView; 
} 

全码：

public class Find extends AppCompatActivity { 

    private SectionsPagerAdapter mSectionsPagerAdapter; 

    private ViewPager mViewPager; 

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


     // Create the adapter that will return a fragment for each of the three 
     // primary sections of the activity. 
     mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 

     // Set up the ViewPager with the sections adapter. 
     mViewPager = (ViewPager) findViewById(R.id.container); 
     mViewPager.setAdapter(mSectionsPagerAdapter); 

     TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs); 
     tabLayout.setupWithViewPager(mViewPager); 

     TabLayout.Tab tab1 = tabLayout.getTabAt(0); 
     tab1.setCustomView(R.layout.icon_view); 
     tab1.setIcon(R.drawable.profile); 

     TabLayout.Tab tab2 = tabLayout.getTabAt(1); 
     tab2.setCustomView(R.layout.icon_view); 
     tab2.setIcon(R.drawable.logo_a); 

     TabLayout.Tab tab3 = tabLayout.getTabAt(2); 
     tab3.setCustomView(R.layout.icon_view); 
     tab3.setIcon(R.drawable.settings); 

    } 

    public static class PlaceholderFragment extends Fragment { 

     private static final String ARG_SECTION_NUMBER = "section_number"; 

     public PlaceholderFragment() { 
     } 

     /** 
     * Returns a new instance of this fragment for the given section 
     * number. 
     */ 
     public static PlaceholderFragment newInstance(int sectionNumber) { 
      PlaceholderFragment fragment = new PlaceholderFragment(); 
      Bundle args = new Bundle(); 
      args.putInt(ARG_SECTION_NUMBER, sectionNumber); 
      fragment.setArguments(args); 
      return fragment; 
     } 

     public static class SettingsFragment extends PreferenceFragment { 
      @Override 
      public void onCreate(Bundle savedInstanceState) { 
       super.onCreate(savedInstanceState); 

       // Load the preferences from an XML resource 
       addPreferencesFromResource(R.xml.preferences); 
      } 

     } 

     @Override 
     public View onCreateView(LayoutInflater inflater, ViewGroup container, 
           Bundle savedInstanceState) { 
      View rootView = null; 
      switch (getArguments().getInt(ARG_SECTION_NUMBER)) { 
       case 1: { 
        rootView = inflater.inflate(R.layout.fragment_profile, container, false); 
        break; 
       } 
       case 2: { 
        rootView = inflater.inflate(R.layout.fragment_find, container, false); 
        break; 
       } 
       case 3: { 
        SettingsFragment fragment = new SettingsFragment(); 
        // what goes here? 
        break; 
       } 
      } 

      return rootView; 
     } 
    } 

    /** 
    * A {@link FragmentPagerAdapter} that returns a fragment corresponding to 
    * one of the sections/tabs/pages. 
    */ 
    public class SectionsPagerAdapter extends FragmentPagerAdapter { 

     public SectionsPagerAdapter(FragmentManager fm) { 
      super(fm); 
     } 

     @Override 
     public Fragment getItem(int position) { 
      // getItem is called to instantiate the fragment for the given page. 
      // Return a PlaceholderFragment (defined as a static inner class below). 
      return PlaceholderFragment.newInstance(position + 1); 
     } 

     @Override 
     public int getCount() { 
      // Show 3 total pages. 
      return 3; 
     } 

Answer 1

1. 独立SettingsFragment从PlaceholderFragment
2. 更新SectionsPagerAdapter的getItem()方法来显示SettingsFragment为3rd TAB。
3. 从onCreateView()删除case 3。

试试这个：

public class Find extends AppCompatActivity { 

    private SectionsPagerAdapter mSectionsPagerAdapter; 

    private ViewPager mViewPager; 

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


     // Create the adapter that will return a fragment for each of the three 
     // primary sections of the activity. 
     mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 

     // Set up the ViewPager with the sections adapter. 
     mViewPager = (ViewPager) findViewById(R.id.container); 
     mViewPager.setAdapter(mSectionsPagerAdapter); 

     TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs); 
     tabLayout.setupWithViewPager(mViewPager); 

     TabLayout.Tab tab1 = tabLayout.getTabAt(0); 
     tab1.setCustomView(R.layout.icon_view); 
     tab1.setIcon(R.drawable.profile); 

     TabLayout.Tab tab2 = tabLayout.getTabAt(1); 
     tab2.setCustomView(R.layout.icon_view); 
     tab2.setIcon(R.drawable.logo_a); 

     TabLayout.Tab tab3 = tabLayout.getTabAt(2); 
     tab3.setCustomView(R.layout.icon_view); 
     tab3.setIcon(R.drawable.settings); 

    } 

    public static class SettingsFragment extends PreferenceFragment { 
     @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 

      // Load the preferences from an XML resource 
      addPreferencesFromResource(R.xml.preferences); 
     } 
    } 

    public static class PlaceholderFragment extends Fragment { 

     private static final String ARG_SECTION_NUMBER = "section_number"; 

     public PlaceholderFragment() { 
     } 

     /** 
     * Returns a new instance of this fragment for the given section 
     * number. 
     */ 
     public static PlaceholderFragment newInstance(int sectionNumber) { 
      PlaceholderFragment fragment = new PlaceholderFragment(); 
      Bundle args = new Bundle(); 
      args.putInt(ARG_SECTION_NUMBER, sectionNumber); 
      fragment.setArguments(args); 
      return fragment; 
     } 

     @Override 
     public View onCreateView(LayoutInflater inflater, ViewGroup container, 
           Bundle savedInstanceState) { 
      View rootView = null; 
      switch (getArguments().getInt(ARG_SECTION_NUMBER)) { 
       case 1: { 
        rootView = inflater.inflate(R.layout.fragment_profile, container, false); 
        break; 
       } 
       case 2: { 
        rootView = inflater.inflate(R.layout.fragment_find, container, false); 
        break; 
       } 

      } 

      return rootView; 
     } 
    } 

    /** 
    * A {@link FragmentPagerAdapter} that returns a fragment corresponding to 
    * one of the sections/tabs/pages. 
    */ 
    public class SectionsPagerAdapter extends FragmentPagerAdapter { 

     public SectionsPagerAdapter(FragmentManager fm) { 
      super(fm); 
     } 

     @Override 
     public Fragment getItem(int position) { 
      // getItem is called to instantiate the fragment for the given page. 
      // Return a PlaceholderFragment (defined as a static inner class below). 
      switch (position) { 
       case 0: { 
        return PlaceholderFragment.newInstance(1); 
       } 
       case 1: { 
        return PlaceholderFragment.newInstance(2); 
       } 
       case 2: { 
        SettingsFragment fragment = new SettingsFragment(); 
        return fragment; 
       } 
      } 

      return PlaceholderFragment.newInstance(1); 
     } 

     @Override 
     public int getCount() { 
      // Show 3 total pages. 
      return 3; 
     } 
    } 
} 

UPDATE：

为了解决这个错误，你必须使用PreferenceFragmentCompat：

要使用PreferenceFragmentCompat，dependencies下你build.gradle文件中添加如下一行：

dependencies { 
    ......... 
    ............... 
    compile 'com.android.support:preference-v7:25.1.0' 
} 

2.扩展您的SettingsFragment从PreferenceFragmentCompat而不是PreferenceFragment。

import android.support.v7.preference.PreferenceFragmentCompat; 

    ......... 
    ................. 

    public static class SettingsFragment extends PreferenceFragmentCompat { 

     @Override 
     public void onCreatePreferences(Bundle savedInstanceState, String rootKey) { 

      // Load the preferences from an XML resource 
      addPreferencesFromResource(R.xml.preferences); 
     } 
    } 

    ......... 
    ................. 

您必须指定preferenceTheme在theme：

styles.xml：

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar"> 
    ....... 
    ........... 
    <item name="preferenceTheme">@style/PreferenceThemeOverlay</item> 
</style> 

您还可以检查tutorial更多地了解PreferenceFragmentCompat。

希望这会有所帮助〜