如何在使用ViewPager时处理ActionBarActivity片段中的AsyncTask？

Question

我正在使用ActionBarActivity创建5个选项卡.我使用ViewPager在SectionsPagerAdapter中使用扩展FragmentPagerAdapter在5个选项卡之间滑动.每个选项卡都有一个带有asynctask的片段,在oncreateview方法中调用.当我在一个片段中时,正在调用其他片段中的asynctask.

我尝试在oncreateview方法中使用toast消息是每个片段而不是asynctask.但错误的片段中错误的吐司消息被触发了.

Oncreate方法代码:

        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());


        mViewPager = (ViewPager) findViewById(R.id.pager_exp); 
        mViewPager.setAdapter(mSectionsPagerAdapter);


        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
                    @Override
                    public void onPageSelected(int position) 
                    {
                        actionBar.setSelectedNavigationItem(position);
                        actionBar.setTitle(getHomePageTitle(position)); 
                    }
                });


        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()
                    .setIcon(getPagedrawable(i))
                    .setTabListener(this));

        }

//适配器类代码:

public class SectionsPagerAdapter extends FragmentPagerAdapter {

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

    @Override
    public Fragment getItem(int position) {


    switch (position) 
    {
        case 0:
            Fragment1 f1 = new Fragment1(); 
            return f1;

        case 1:
            Fragment2 f2 = new Fragment2(); 
            return f2;

        case 2:
            Fragment3 f3 = new Fragment3();  
            return f3;

        case 3: 
            Fragment4 f4 = new Fragment4();
            return f4;


        case 4: 
            Fragment5 f5 = new Fragment5();
            return f5;

        }

        return null;

    }

    @Override
    public int getCount() {
        // Show 5 total pages.
        return 5;  
    } 


}

Fragemnt类代码:

public class F1 extends Fragment 
{
@Override
public void onCreate(Bundle savedInstanceState)  
{
    super.onCreate(savedInstanceState);

}

 @SuppressLint("NewApi")
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) 
{ 
    View view       = inflater.inflate(R.layout.f1,container, false);

     Toast.makeText(getActivity(), "F1", Toast.LENGTH_SHORT).show();
    return view;  
}   
}

Answer 1

在FragmentPagerAdapter保持额外的片段,除了所示的一个,在恢复状态.解决方案是实现自定义OnPageChangeListener并为显示片段时创建新方法.

1)创建LifecycleManager接口接口将有两个方法,每个ViewPager’sFragment将实现它.这些方法如下:

public interface FragmentLifecycle {

    public void onPauseFragment();
    public void onResumeFragment();

}

2)让每个Fragment实现每个类声明的接口Add iplements语句:

public class FragmentBlue extends Fragment implements FragmentLifecycle
public class FragmentGreen extends Fragment implements FragmentLifecycle
public class FragmentPink extends Fragment implements FragmentLifecycle

3)在每个片段中实现接口方法为了检查它是否真的按预期工作,我将只记录方法调用并显示Toast:

@Override
public void onPauseFragment() {
    Log.i(TAG, "onPauseFragment()");
    Toast.makeText(getActivity(), "onPauseFragment():" + TAG, Toast.LENGTH_SHORT).show(); 
}

@Override
public void onResumeFragment() {
    Log.i(TAG, "onResumeFragment()");
    Toast.makeText(getActivity(), "onResumeFragment():" + TAG, Toast.LENGTH_SHORT).show(); 
}

4)在ViewPager页面上调用接口方法更改您可以在ViewPager上设置OnPageChangeListener,并在每次ViewPager显示另一个页面时获取回调:

pager.setOnPageChangeListener(pageChangeListener);

5)实现OnPageChangeListener以调用自定义生命周期方法

监听器知道新位置,并可以在PagerAdapter的帮助下调用新Fragment上的接口方法.我可以在这里调用onResumeFragment()来获取当前新片段和onPauseFragment().

我还需要存储当前片段的位置(最初当前位置等于0),因为我不知道用户是从左向右还是从右向左滚动.看看我在代码中的意思:

private OnPageChangeListener pageChangeListener = new OnPageChangeListener() {

    int currentPosition = 0;

    @Override
    public void onPageSelected(int newPosition) {

        FragmentLifecycle fragmentToShow = (FragmentLifecycle)pageAdapter.getItem(newPosition);
        fragmentToShow.onResumeFragment();

        FragmentLifecycle fragmentToHide = (FragmentLifecycle)pageAdapter.getItem(currentPosition);
        fragmentToHide.onPauseFragment();

        currentPosition = newPosition;
    }

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

    public void onPageScrollStateChanged(int arg0) { }
};

我没有写代码.完整的教程:http://looksok.wordpress.com/2013/11/02/viewpager-with-detailed-fragment-lifecycle-onresumefragment-including-source-code/