android pager片段意外行爲

Question

我基本上覆制粘貼實現swiper的活動。我添加的代碼是測試增量。這是發生了什麼：

應用程序啓動（我向左和向右滑動：

第1部分：1

第2部分：1

Seciton 3：1（一切都很好達貝雷）

第2部分：1（爲什麼不是這個2，它遞增）

第1節：2

部分2：1（再次，它1）

部分3：2

部分2：1

第1節：3

部分2：1

第3節：3

數字增量的方式沒有意義。我多次登陸第2部分，test類屬性應該增加，但沒有增加。這是怎麼回事？

package activities; 

import android.app.ActionBar; 
import android.app.Activity; 
import android.app.Fragment; 
import android.app.FragmentManager; 
import android.app.FragmentTransaction; 
import android.os.Bundle; 
import android.support.v13.app.FragmentPagerAdapter; 
import android.support.v4.view.ViewPager; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.TextView; 

import com.comp.chat.R; 

import java.util.Locale; 

public class SplashActivity extends Activity implements ActionBar.TabListener { 

    /** 
    * The {@link android.support.v4.view.PagerAdapter} that will provide 
    * fragments for each of the sections. We use a 
    * {@link 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.v13.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_splash); 

     // 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 activity. 
     mSectionsPagerAdapter = new SectionsPagerAdapter(getFragmentManager()); 

     // 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 
    public boolean onCreateOptionsMenu(Menu menu) { 

     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.splash, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 
     if (id == R.id.action_settings) { 
      return true; 
     } 
     return super.onOptionsItemSelected(item); 
    } 

    @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. 
      // 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; 
     } 

     @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 placeholder fragment containing a simple view. 
    */ 
    public static class PlaceholderFragment extends Fragment { 
     /** 
     * The fragment argument representing the section number for this 
     * fragment. 
     */ 
     private static final String ARG_SECTION_NUMBER = "section_number"; 

     private int test = 0; 

     /** 
     * 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 PlaceholderFragment() { 
     } 

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

} 

Answer 1

好吧，這很容易。在viewPager中，您將視圖存儲在內存中。當前選中，左邊一個，右邊一個。如果從3→2比第2部分滑動，已經創建了視圖，所以不需要再創建它，因此測試保持相同的值。如果你滑動以獲得第1部分，比從零開始重新創建，並且測試編號爲1. 檢查了這一點：http://developer.android.com/reference/android/support/v4/view/ViewPager.html#setOffscreenPageLimit(int)