如何选择我们在操作栏中选择的上一个标签？

Question

这里我的问题不好解释。首先选择第一个选项卡，然后如果我点击第二个选项卡，它的工作正常，但再次单击第一个选项卡我的应用程序将被关闭。你可以建议我吗？ 这是我的代码。

public class MainActivity extends Activity {
    public static Context appContext;


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    appContext = getApplicationContext();


    ActionBar actionbar = getActionBar();
    actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    ActionBar.Tab connectionTab = actionbar.newTab().setText("Connection");
    ActionBar.Tab masterDataTab = actionbar.newTab().setText("Master Data");

    Fragment connection = new AFragment();
    Fragment masterData = new BFragment();

    connectionTab.setTabListener(new MyTabsListener(connection));
    masterDataTab.setTabListener(new MyTabsListener(masterData));

    actionbar.addTab(connectionTab);
    actionbar.addTab(masterDataTab);
}

@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()) {
            }
            return false;
    }

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt("tab", getActionBar().getSelectedNavigationIndex());
}

}


 class MyTabsListener implements ActionBar.TabListener {
    public Fragment fragment;

    public MyTabsListener(Fragment fragment) {
            this.fragment = fragment;
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
            Toast.makeText(MainActivity.appContext, "Reselected!", Toast.LENGTH_LONG).show();
   //ft.replace(R.id.fragment_container, fragment);
    }

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

        ft.replace(R.id.fragment_container, fragment);  

    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        ft.remove(fragment);
    }

 }