android片段3頁

Question

嗯，我是新來的Android，我想做一個3頁的刷卡應用程序。我從eclipse創建了一個新項目，並使用固定選項卡和可滾動頁面選擇了項目。我刪除了這些標籤，因爲我只想要一個應用程序與可滾動頁面。下面的代碼

在MainActivity類

@SuppressLint("ValidFragment") 
      public class MainActivity extends FragmentActivity { 


SectionsPagerAdapter mSectionsPagerAdapter; 

/** 
* The {@link ViewPager} that will host the section contents. 
*/ 
ViewPager mViewPager; 

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

    final int PAGE_COUNT=3; 

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

    // Set up the ViewPager with the sections adapter. 
    mViewPager = (ViewPager) findViewById(R.id.pager); 
    mViewPager.setAdapter(mSectionsPagerAdapter); 
    mViewPager.setOffscreenPageLimit(3); 
    // When swiping between different sections, select the corresponding 
    // tab. We can also use ActionBar.Tab#select() to do this if we have 
    // a reference to the Tab. 
    mViewPager 
      .setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() { 
       @Override 
       public void onPageSelected(int position) { 

       } 
      }); 

    // For each of the sections in the app, add a tab to the action bar. 
    for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) { 
     // Create a tab with text corresponding to the page title defined by 
     // the adapter. Also specify this Activity object, which implements 
     // the TabListener interface, as the callback (listener) for when 
     // this tab is selected. 

    } 
} 




/** 
* 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) { 
     Fragment fragment = null; 
     switch(position) { 
     case 0: 
      fragment = Fragment.instantiate(getBaseContext(), first.class.getName()); 
      break; 
     case 1: 
      fragment = Fragment.instantiate(getBaseContext(), second.class.getName()); 
      break;    
     case 2: 
      fragment = Fragment.instantiate(getBaseContext(), MainActivity.class.getName()); 
      break;   } 
    return fragment;  
    } 

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

    } 


    @Override 
    public CharSequence getPageTitle(int position) { 
     Locale l = Locale.getDefault(); 
     switch (position) { 
     case 0: 
      return getString(R.string.title_section1).toUpperCase(l); 
     case 1: 
      return getString(R.string.title_section2).toUpperCase(l); 
     case 2: 
      return getString(R.string.title_section3).toUpperCase(l); 
     } 
     return null; 
    } 
} 

/** 
* A dummy fragment representing a section of the app, but that simply 
* displays dummy text. 
*/ 
public static class DummySectionFragment extends Fragment { 
    /** 
    * The fragment argument representing the section number for this 
    * fragment. 
    */ 
    public static final String ARG_SECTION_NUMBER = "section_number"; 

    public DummySectionFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
      Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_main_dummy, 
       container, false); 
     TextView dummyTextView = (TextView) rootView 
       .findViewById(R.id.section_label); 
     dummyTextView.setText(Integer.toString(getArguments().getInt(
       ARG_SECTION_NUMBER))); 
     return rootView; 
    } 
} 

這是一個片段first.java

 public class first extends FragmentActivity{ 


    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 

     // here you can load whatever layout you want for your fragment 
     View v = inflater.inflate(R.layout.prva, container, false); 
     return v; 
    }} 

錯誤我：

10-30 14:46:20.355: E/AndroidRuntime(7828): android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment com.example.swipe.MainActivity$SectionsPagerAdapter$good: make sure class name exists, is public, and has an empty constructor that is public 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.support.v4.app.Fragment.instantiate(Fragment.java:413) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.support.v4.app.Fragment.instantiate(Fragment.java:377) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at com.example.swipe.MainActivity$SectionsPagerAdapter.getItem(MainActivity.java:91) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:97) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:832) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.support.v4.view.ViewPager.populate(ViewPager.java:982) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.support.v4.view.ViewPager.populate(ViewPager.java:914) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.view.View.measure(View.java:15473) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5056) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.view.View.measure(View.java:15473) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.widget.LinearLayout.measureVertical(LinearLayout.java:833) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.widget.LinearLayout.onMeasure(LinearLayout.java:574) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.view.View.measure(View.java:15473) 
10-30 14:46:20.355: E/AndroidRuntime(7828):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5056) 

Answer 1

您的代碼似乎是正確的。 我認爲你的問題與構建路徑和庫有關android-support-v4.jar 有時候（對於我來說，在eclipse中）如果你在libs文件夾中有一個jar文件，項目編譯，但是如果你沒有在構建路徑中包含正確的文件，那麼項目在運行時崩潰。

您可以檢查是否在屬性 - Java構建路徑 - 訂單和出口 - Android的支持，v4.jar必須存在檢查和高達