java - Android如何在标签更改时停止刷新 fragment

Question

我有以下代码:

MainActivity.java

package com.erc.library;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;

import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.FragmentTransaction;
import android.content.SharedPreferences;
import android.content.res.Resources;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Environment;
import android.os.StrictMode;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Toast;

import com.erc.sayeghlibrary.adapter.TabsPagerAdapter;

public class MainActivity extends FragmentActivity implements
        ActionBar.TabListener {

    private ViewPager viewPager;
    private TabsPagerAdapter mAdapter;
    private ActionBar actionBar;
    // Tab titles
    private String[] tabs = { "Stories", "Dictionaries", "eBooks"};

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






        int actionBarTitleId = Resources.getSystem().getIdentifier("action_bar_title", "id", "android");
        if (actionBarTitleId > 0) {
            TextView title = (TextView) findViewById(actionBarTitleId);
            if (title != null) {
                title.setTextColor(Color.WHITE);
            }
        }       

        // Initilization
        viewPager = (ViewPager) findViewById(R.id.pager);
        actionBar = getActionBar();
        mAdapter = new TabsPagerAdapter(getSupportFragmentManager());

        viewPager.setAdapter(mAdapter);
        actionBar.setHomeButtonEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);


        // Adding Tabs
        for (String tab_name : tabs) {
            actionBar.addTab(actionBar.newTab().setText(tab_name)
                    .setTabListener(this));
        }

        /**
         * on swiping the viewpager make respective tab selected
         * */
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

            @Override
            public void onPageSelected(int position) {
                // on changing the page
                // make respected tab selected
                actionBar.setSelectedNavigationItem(position);
            }

            @Override
            public void onPageScrolled(int arg0, float arg1, int arg2) {
            }

            @Override
            public void onPageScrollStateChanged(int arg0) {
            }
        });







    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        // on tab selected
        // show respected fragment view
        viewPager.setCurrentItem(tab.getPosition());


    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
    }






       @Override
       public boolean onCreateOptionsMenu(Menu menu) {
         MenuInflater inflater = getMenuInflater();
         inflater.inflate(R.menu.main, menu);
         return true;
       } 




       @Override
       public boolean onOptionsItemSelected(MenuItem item) {
         switch (item.getItemId()) {
         // action with ID action_refresh was selected
         case R.id.Favorites:
           Toast.makeText(this, "Favorites selected", Toast.LENGTH_SHORT)
               .show();
           break;
         // action with ID action_settings was selected

         default:
           break;
         }

         return true;
       } 


}

TabsPagerAdapter.java

package com.erc.library.adapter;

import com.erc.library.Dictionaries;
import com.erc.library.Ebooks;
import com.erc.library.Stories;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;

public class TabsPagerAdapter extends FragmentPagerAdapter {

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

    @Override
    public Fragment getItem(int index) {

        switch (index) {
        case 0:

            return new Stories();
        case 1:

            return new Dictionaries();
        case 2:
            // Movies fragment activity
            return new Ebooks();
        }

        return null;
    }

    @Override
    public int getCount() {
        // get item count - equal to number of tabs
        return 3;
    }

}

我正在制作一个按标签导航的库应用程序，问题是每次我从第三个标签转到第一个或第一个到第三个时，标签内容都在刷新，我想防止刷新，有什么帮助吗？

Answer 1

默认情况下，ViewPager 会在您滑动页面时重新创建 fragment 。为了防止这种情况，您可以尝试以下三种方法之一:

1.在 fragment 的onCreate()中，调用setRetainInstance(true)。

2. 如果 fragment 数量固定且相对较少，则在您的 onCreate() 中添加以下代码:

mViewPager = (ViewPager)findViewById(R.id.pager);
mViewPager.setOffscreenPageLimit(limit);         /* limit is a fixed integer*/

3. 使用 FragmentPagerAdapter作为 ViewPager 的一部分。

如果我没记错的话，第二种选择更有希望。但我强烈建议您尝试所有这三种方法，看看它们中的哪一种有效。