java 检查片段是否存在并重用它
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Check if a fragment exists and reuse it
提问by Usi Usi
I'm using the following code to create a fragment everytime the user click on an item in a list view. But in this way the fragment is created at every user click. What I want is to reuse the old fragment (if it exists) and only reload its content (don't create a new one).
每次用户单击列表视图中的项目时，我都使用以下代码创建一个片段。但是通过这种方式，在每次用户点击时都会创建片段。我想要的是重用旧片段（如果存在）并且只重新加载其内容（不要创建新片段）。
MagazineViewFragment fragment = new MagazineViewFragment();
fragment.openStream(itemSelected);
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, fragment)
.commit();
How can I do?
我能怎么做？
回答by reVerse
There're multiple ways, probably the most easy one is to check if the current Fragment in your containeris an instance of FragmentXYZ (in your case MagazineViewFragment).
有多种方法，可能最简单的方法是检查您当前的 Fragment 是否是 FragmentXYZcontainer的实例（在您的情况下MagazineViewFragment）。
Example
例子
Fragment mFragment = getFragmentManager().findFragmentById(R.id.container);
if (mFragment instanceof MagazineViewFragment)
return;
回答by Thomas R.
Something like this might help:
像这样的事情可能会有所帮助：
getFragmentManager().findFragmentById(fragmentId);
Do not forget the null check.
不要忘记空检查。
回答by QArea
Add tag when you call your fragment from activity:
从活动调用片段时添加标签：
FragmentManager fm = getFragmentManager();
Fragment fragment = fm.findFragmentByTag( MagazineViewFragment.TAG);
if (fragment == null) {
MagazineViewFragment fragment = new MagazineViewFragment();
fragment.openStream(itemSelected);
getFragmentManager()
.beginTransaction()
.add(R.id.container, fragment, MagazineViewFragment.TAG)
.commit();
}
If you need only to update itemSelected - see broadcasts or listeners.
如果您只需要更新 itemSelected - 请参阅广播或侦听器。
