实现ActionBar导航列表+ ListFragment

Question

应用程序应下载数据并将其输入listFragment obj，但仅对ActionBar下拉列表中的第一项“ Today”执行此操作。 当我选择第二项时，“很快”应用会因错误而崩溃。

03-21 14:53:05.272: E/AndroidRuntime(5289): FATAL EXCEPTION: main
03-21 14:53:05.272: E/AndroidRuntime(5289): java.lang.IllegalStateException: commit already called

我了解多次调用commit()会导致该错误，但是没有提交数据将不会显示在屏幕上。 请帮助我，我不知道如何解决。 任何帮助将不胜感激。

公共类MainActivity扩展了Activity {

    ParkFragment mFragment;
    ParkFragment mFragment2;
    FragmentTransaction transaction = getFragmentManager().beginTransaction();

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

        final String[] actions = new String[] {"Today","Soon"};
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getBaseContext(), android.R.layout.simple_spinner_dropdown_item, actions);

        ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);

        ActionBar.OnNavigationListener navigationListener = new OnNavigationListener() {

            @Override
            public boolean onNavigationItemSelected(int itemPosition, long itemId) {
                if (actions[itemPosition] == "Today"){
                    if (mFragment2 != null){transaction.detach(mFragment2);}
                    if (mFragment == null){
                        mFragment = new ParkFragment("url1",MainActivity.this);
                        transaction.add(android.R.id.content, mFragment);
                        transaction.commit();
                    }else{
                        transaction.attach(mFragment);
                        transaction.commit();
                    }
                   }
                   if (actions[itemPosition]== "Soon"){
                       if (mFragment != null){transaction.detach(mFragment);
                       System.out.println("Detached");}
                    if (mFragment2 == null){
                        mFragment2 = new ParkFragment("url2",MainActivity.this);
                        transaction.add(android.R.id.content, mFragment2);
                        transaction.commit();
                    }else{
                        transaction.attach(mFragment2);
                        transaction.commit();
                    }       
                }
                return true;
            }
        };

        actionBar.setListNavigationCallbacks(adapter, navigationListener);

        }

Answer 1

将FragmentTransaction设为局部变量，而不是成员变量。

PSUEDO：

if (...) {
   FragmentTransaction transaction = getFragmentManager().beginTransaction(); 
   //add.. do stuff
   transaction.commit();
} else {
   FragmentTransaction transaction = getFragmentManager().beginTransaction(); 
   //add.. do stuff
   transaction.commit();
}