的Android如何知道什麼時候你的標籤已獲得焦點，

Question

我有一個標籤視圖在我的活動，

目前，我在我的片段onCreateView做一個UI更新，但我不認爲這是正確的地方。

是否有我可以重載的方法，當我的標籤獲得視圖時會調用它？因此，當我的用戶點擊或滾動到我的標籤時，我可以輪詢我的服務器並更新我的視圖。

一些簡化代碼：

@SuppressLint("NewApi") 
public class Rhino68PanelActivity extends FragmentActivity implements ActionBar.TabListener { 

static String TAG = "Rhino68PanelActivty"; 

/** 
* The {@link android.support.v4.view.PagerAdapter} that will provide 
* fragments for each of the sections. We use a 
* {@link android.support.v4.app.FragmentPagerAdapter} derivative, which 
* will keep every loaded fragment in memory. If this becomes too memory 
* intensive, it may be best to switch to a 
* {@link android.support.v4.app.FragmentStatePagerAdapter}. 
*/ 
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_rhino68_panel); 

    // Set up the action bar. 
    final ActionBar actionBar = getActionBar(); 
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 

    // 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); 

    // 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) { 
      actionBar.setSelectedNavigationItem(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. 
     actionBar.addTab(actionBar.newTab().setText(mSectionsPagerAdapter.getPageTitle(i)).setTabListener(this)); 
    } 
} 

@Override 
protected void onDestroy() { 
    super.onDestroy(); 
    Network.cancelRequests(Rhino68PanelActivity.this); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.rhino68_panel, menu); 
    return true; 
} 

@Override 
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { 
    // When the given tab is selected, switch to the corresponding page in 
    // the ViewPager. 
    mViewPager.setCurrentItem(tab.getPosition()); 
} 

@Override 
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { 
} 

@Override 
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { 
} 

/** 
* 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. 
     Fragment fragment = null; 

     switch (position) { 
     case 0: { 
      fragment = new OneSectionFragment(); 
     } 
      break; 
     case 1: { 
      fragment = new TwoSectionFragment(); 
     } 
      break; 
     case 2: { 
      fragment = new ThreeSectionFragment(); 
     } 
      break; 
     default: { 
      fragment = new OneSectionFragment(); 
     } 
     } 
     return fragment; 
    } 

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

    @Override 
    public CharSequence getPageTitle(int position) { 
     Locale l = Locale.getDefault(); 
     switch (position) { 
     case 0: 
      return "1"; 
     case 1: 
      "2"; 
     case 2: 
      "3"; 
     } 
     return null; 
    } 
} 

public static class oneSectionFragment extends Fragment { 


    private static Context mContext; 

    public StatusSectionFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_rhino68_panel_status, container, false); 
     mContext = getActivity(); 
     // update view 
     .... 
     return rootView; 
    } 
    //fucntions and methods 
} 

    public static class twoSectionFragment extends Fragment { 


    private static Context mContext; 

    public StatusSectionFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_rhino68_panel_status, container, false); 
     mContext = getActivity(); 
     // update view 
     .... 
     return rootView; 
    } 
    //fucntions and methods 
} 

Answer 1

問題1：知道哪些選項卡具有焦點

解決方案：您的ViewPager上的setOnPageChangeListener。使用收到的索引，您知道哪個選項卡處於活動狀態。

問題2：如何從活動頁面執行的方法（片段）

解決方案：

1. 創建您的viewpager適配器一個公共方法：onNewTabSelected（INT指數）
2. 創建（私人MyTabFragment tabFragment;）
3. 與索引，你知道你應該使用哪個片段
4. 創建一個公共的方法OD在您的片段
5. 執行新創建的方法這種方法，您轉接器內

Answer 2

您可以通過使用更新每個SectionFragment您的看法：

@Override 
public void setUserVisibleHint(boolean isVisibleToUser) { 
    super.setUserVisibleHint(isVisibleToUser); 
    if (isVisibleToUser) { } 
    else { } 
} 

@see：How to determine when Fragment becomes visible in ViewPager