返回上一个片段无法正常工作

Question

我正在使用导航抽屉，当我选择一个项目时，它会正确地将前一个片段替换为我选择的片段，但是如果我打开另一个片段，然后单击后退按钮，它会转到上一个活动之前的片段，它这样做有什么问题？

private void selectItem(int position) {
    Fragment newFragment;
    FragmentTransaction transaction = getFragmentManager().beginTransaction();
    switch (position){
        case 0:
            //Update
            newFragment = new UpdateFragment();
            transaction.replace(R.id.content_frame, newFragment);
            transaction.addToBackStack(null);
            transaction.commit();
            listView.setItemChecked(position, true);
            setTitle(navigationDrawerItems[position]);
            break;
        case 1:
            //Maps
            newFragment = new TimetableFragment();
            transaction.replace(R.id.content_frame, newFragment);
            transaction.addToBackStack(null);
            transaction.commit();
            listView.setItemChecked(position, true);
            setTitle(navigationDrawerItems[position]);
            break;
        case 2:
            //Timetables
            newFragment = new TimetableFragment();
            transaction.replace(R.id.content_frame, newFragment);
            transaction.addToBackStack(null);
            transaction.commit();
            listView.setItemChecked(position, true);
            setTitle(navigationDrawerItems[position]);
            break;
        case 3:
            //Notes
            newFragment = new TimetableFragment();
            transaction.replace(R.id.content_frame, newFragment);
            transaction.addToBackStack(null);
            transaction.commit();
            listView.setItemChecked(position, true);
            setTitle(navigationDrawerItems[position]);
            break;
        case 4:
            //About
            newFragment = new AboutFragment();
            transaction.replace(R.id.content_frame, newFragment);
            transaction.addToBackStack(null);
            transaction.commit();
            listView.setItemChecked(position, true);
            setTitle(navigationDrawerItems[position]);
            break;
        case 5:
            //Settings
            newFragment = new SettingsFragment();
            transaction.replace(R.id.content_frame, newFragment);
            transaction.addToBackStack(null);
            transaction.commit();
            listView.setItemChecked(position, true);
            setTitle(navigationDrawerItems[position]);
            break;
    }
    //listView.setItemChecked(position, true);
    //setTitle(navigationDrawerItems[position]);
    drawerLayout.closeDrawer(listView);
}

Answer 1

您可以在onBackPressed 中使用getFragmentManager().popBackStack() 方法：

@Override
public void onBackPressed() {
    if (getFragmentManager().getBackStackEntryCount() > 0) {
         getFragmentManager().popBackStack();
         getFragmentManager().beginTransaction().commit();
    }
    else {
        super.onBackPressed();
    }
}

不要忘记在 BackStack 中添加片段，例如：

transaction.addToBackStack(null);

编辑：

要在操作栏中显示当前片段名称，您可以在 FragmentActivity 的onResume 上获取它：

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();

    FragmentManager fragManager = this.getSupportFragmentManager();
    int count = this.getSupportFragmentManager().getBackStackEntryCount();

    // Fetch last fragment
    Fragment fragment = fragManager.getFragments().get(count>0?count-1:count);

    // Check with your possible Fragment class
    if( fragment instanceof OneFragment)
    {
        setTitle("OneFragment");
    }
    else if(fragment instanceof TwoFragment)
    {
        setTitle("TwoFragment");
    }
}

希望对你有所帮助ツ

Answer 2

您正在将 null 添加到后台堆栈 -

transaction.addToBackStack(null);

用你的片段的标签名称替换这个空值。

它会起作用的。