我正在学习如何使用片段。我Fragment
在类的顶部初始化了三个实例。我将片段添加到这样的活动中:
声明和初始化:
Fragment A = new AFragment();
Fragment B = new BFragment();
Fragment C = new CFragment();
替换/添加:
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, A);
ft.addToBackStack(null);
ft.commit();
这些片段工作正常。每个片段都附加到活动中,并毫无问题地保存到后台堆栈。
所以当我启动A
, C
, 然后B
时,堆栈看起来像这样:
| |
|B|
|C|
|A|
___
当我按下“后退”按钮时,B
会被破坏并C
恢复。
但是,当我第二次启动片段A
时,它不是从后台堆栈恢复,而是添加到后台堆栈的顶部
| |
|A|
|C|
|A|
___
但我想恢复A
并销毁它上面的所有碎片(如果有的话)。实际上,我只是喜欢默认的回栈行为。
我该如何做到这一点?
预期:(A
应该恢复并且应该销毁顶部片段)
| |
| |
| |
|A|
___
编辑:(由 A--C 建议)
这是我的尝试代码:
private void selectItem(int position) {
Fragment problemSearch = null, problemStatistics = null;
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
String backStateName = null;
Fragment fragmentName = null;
boolean fragmentPopped = false;
switch (position) {
case 0:
fragmentName = profile;
break;
case 1:
fragmentName = submissionStatistics;
break;
case 2:
fragmentName = solvedProblemLevel;
break;
case 3:
fragmentName = latestSubmissions;
break;
case 4:
fragmentName = CPExercise;
break;
case 5:
Bundle bundle = new Bundle();
bundle.putInt("problem_no", problemNo);
problemSearch = new ProblemWebView();
problemSearch.setArguments(bundle);
fragmentName = problemSearch;
break;
case 6:
fragmentName = rankList;
break;
case 7:
fragmentName = liveSubmissions;
break;
case 8:
Bundle bundles = new Bundle();
bundles.putInt("problem_no", problemNo);
problemStatistics = new ProblemStatistics();
problemStatistics.setArguments(bundles);
fragmentName = problemStatistics;
default:
break;
}
backStateName = fragmentName.getClass().getName();
fragmentPopped = manager.popBackStackImmediate(backStateName, 0);
if (!fragmentPopped) {
ft.replace(R.id.content_frame, fragmentName);
}
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(backStateName);
ft.commit();
// I am using drawer layout
mDrawerList.setItemChecked(position, true);
setTitle(title[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
问题是,当我启动A
然后B
按“返回”时,B
将被删除并A
恢复。并再次按“返回”应退出应用程序。但它显示一个空白窗口,我必须第三次按下才能关闭它。
另外,当我启动时A
,然后B
,然后C
,然后B
再...
预期的:
| |
| |
|B|
|A|
___
实际的:
| |
|B|
|B|
|A|
___
我应该用任何自定义覆盖onBackPressed()
还是我错过了什么?