定向改变后片段无法正常工作

Question

我遇到问题Fragments和方向改变.

我有一个应用程序,MainActivity它Fragments通过选项卡式操作栏处理切换.以下是选项卡式操作栏的代码以及选择选项卡的时间.

private class MyTabListener <T extends android.support.v4.app.Fragment> implements ActionBar.TabListener {
    private android.support.v4.app.Fragment mFragment;
    private final Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;

    public MyTabListener(SherlockFragmentActivity activity, String tag, Class<T> clz) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
    }

    @Override
    public void onTabSelected(Tab tab, android.support.v4.app.FragmentTransaction ft) {
        if (mFragment == null){ // check to see if the fragment has already been initialised. If not create a new one.
            mFragment = android.support.v4.app.Fragment.instantiate(mActivity, mClass.getName());
            ft.add(android.R.id.content,mFragment,mTag);
        } else {
            ft.attach(mFragment); // if the fragment has been initialised attach it to the current activity
        }
    }

    @Override
    public void onTabUnselected(Tab tab, android.support.v4.app.FragmentTransaction ft) {
        if (mFragment != null){
            ft.detach(mFragment); // when a fragment is no longer needed, detach it from the activity but dont destroy it
        }
    }

    @Override
    public void onTabReselected(Tab tab, android.support.v4.app.FragmentTransaction ft) {

    }

我看到的方式是,当应用程序首次以纵向模式加载时,一切正常.当我旋转时,由于某种原因Fragment1添加了另一个实例,然后在选择另一个选项卡时不会分离.当我然后旋转回肖像时也是这种情况.

我已经尝试使用setRetainInstance(true);我的Fragments,但是,这并不工作.

是否有一种方法我需要Fragments在旋转之前覆盖或做一些事情？

提前致谢.

编辑我现在已经看到在重新创建活动时再次调用onTabSelected.这可能是我的问题的原因,片段连接不止一次？

这是我的活动onCreate方法.

super.onCreate(savedInstanceState);

        if (savedInstanceState == null) {
           //setContentView(R.layout.main);

        }
     // Create the Action Bar with tabs
        ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        actionBar.setDisplayShowTitleEnabled(false);
        //create the tab for track and add it to the action bar.
        Tab tab = actionBar.newTab()
                            .setText("Track")
                            .setTabListener(new MyTabListener<TrackingFragment>(this,"track",TrackingFragment.class));
        actionBar.addTab(tab);

        //create the tab for ski tracks and add it to the action bar.
        tab = actionBar.newTab()
                        .setText("Something Tracks")
                        .setTabListener(new MyTabListener<TrackListFragment>(this,"somethingtracks",TrackListFragment.class));
        actionBar.addTab(tab);

        //create the tab for photos and add it to the action bar.
        tab = actionBar.newTab()
                        .setText("Photos")
                        .setTabListener(new MyTabListener<PhotoFragment>(this,"photos",PhotoFragment.class));
        actionBar.addTab(tab);

Answer 1

简短修复:

在该onTabSelected方法中,在使用之前,if (mFragment == null)您需要尝试获取片段(使用mFragment = getSupportFragmentManager().findFragmentByTag(mTag)).你也可以从外面设置这个,但我不认为你这样做.

检查if(savedInstanceState == null)上onCreate也可以解决这个问题,我认为这是一个更好的办法,但!:)

Answer 2

听起来你的onCreate方法中没有包含a的东西if(savedInstanceState == null),所以除了从savedInstanceState包中恢复的片段外,你还要创建另一个片段.

编辑

仔细查看你的代码,我认为我对onCreate有误,你的onTabSelected应该处理它.我认为你if (mFragment == null)的总是空的,因为你没有尝试找到片段.将该代码部分更改为:

@Override 
public void onTabSelected(Tab tab, android.support.v4.app.FragmentTransaction ft) { 

    mFragment = mActivity.getSupportFragmentManager().findFragmentByTag(mTag);   // add this

    if (mFragment == null){ // check to see if the fragment has already been initialised. If not create a new one. 
        mFragment = android.support.v4.app.Fragment.instantiate(mActivity, mClass.getName()); 
        ft.add(android.R.id.content,mFragment,mTag); 
    } else { 
        ft.attach(mFragment); // if the fragment has been initialised attach it to the current activity 
    } 
}