我在Android中玩碎片。
我知道我可以通过使用以下代码更改一个片段:
FragmentManager fragMgr = getSupportFragmentManager();
FragmentTransaction fragTrans = fragMgr.beginTransaction();
MyFragment myFragment = new MyFragment(); //my custom fragment
fragTrans.replace(android.R.id.content, myFragment);
fragTrans.addToBackStack(null);
fragTrans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
fragTrans.commit();
我的问题是，在Java文件中，如何获得当前显示的片段实例?
当前回答
如果你有嵌套片段，如viewpagers内部viewpagers等 你想要得到所有嵌套的片段。
感谢Matt Mombrea的好意，回答一个稍微调整的版本。
private List<Fragment> getVisibleFragments(List<Fragment> searchFragments, List<Fragment> visibleFragments) {
if (searchFragments != null && searchFragments.size() > 0) {
for (Fragment fragment : searchFragments) {
List<Fragment> nestedFragments = new ArrayList<>();
List<Fragment> childFMFragments = fragment.getChildFragmentManager().getFragments();
List<Fragment> fmFragments = fragment.getFragmentManager().getFragments();
fmFragments.retainAll(childFMFragments);
nestedFragments.addAll(childFMFragments);
nestedFragments.addAll(fmFragments);
getVisibleFragments(nestedFragments, visibleFragments);
if (fragment != null && fragment.isVisible()) {
visibleFragments.add(fragment);
}
}
}
return visibleFragments;
}
用法如下:
List<Fragment> allVisibleFragments = getVisibleFragments(searchFragments, visibleFragments);
例如:
List<Fragment> visibleFragments = new ArrayList<>();
List<Fragment> searchFragments = MainActivity.this.getSupportFragmentManager().getFragments();
Toast.makeText(this, ""+getVisibleFragments(searchFragments, visibleFragments), Toast.LENGTH_LONG).show();
其他回答
如果你正在使用AndroidX导航:
val currentFragment = findNavController(R.id.your_navhost)?.currentDestination
有关此导航组件的更多信息: https://developer.android.com/guide/navigation/navigation-getting-started
这是获得当前片段的简单方法。
getFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
@Override public void onBackStackChanged() {
currentFragment = fragmentManager.findFragmentById(R.id.content);
if (currentFragment != null && (currentFragment instanceof LoginScreenFragment)) {
logout.setVisibility(View.GONE);
} else {
logout.setVisibility(View.VISIBLE);
}
}
});
1)
ft.replace(R.id.content_frame, fragment, **tag**).commit();
2)
FragmentManager fragmentManager = getSupportFragmentManager();
Fragment currentFragment = fragmentManager.findFragmentById(R.id.content_frame);
3)
if (currentFragment.getTag().equals(**"Fragment_Main"**))
{
//Do something
}
else
if (currentFragment.getTag().equals(**"Fragment_DM"**))
{
//Do something
}
如果你在使用Kotlin:
var fragment = supportFragmentManager.findFragmentById(R.id.fragment_container)
R.id.fragment_container是片段在其活动中呈现的id
或者如果你想要一个更好的解决方案:
supportFragmentManager.findFragmentById(R.id.content_main)?.let {
// the fragment exists
if (it is FooFragment) {
// The presented fragment is FooFragment type
}
}
我用什么来寻找当前显示片段是在下面的代码。这很简单，现在对我来说很有用。它运行在持有片段的活动中
FragmentManager fragManager = this.getSupportFragmentManager();
int count = this.getSupportFragmentManager().getBackStackEntryCount();
Fragment frag = fragManager.getFragments().get(count>0?count-1:count);
