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
In the main activity, the onAttachFragment(Fragment fragment) method is called when a new fragment is attached to the activity. In this method, you can get the instance of the current fragment. However, the onAttachFragment(Fragment fragment) method is not called when a fragment is popped off the back stack, ie, when the back button is pressed to get the top fragment on top of the stack. I am still looking for a callback method that is triggered in the main activity when a fragment becomes visible inside the activity.
其他回答
我的方法是基于try / catch，如下所示:
MyFragment viewer = null;
if(getFragmentManager().findFragmentByTag(MY_TAG_FRAGMENT) instanceOf MyFragment){
viewer = (MyFragment) getFragmentManager().findFragmentByTag(MY_TAG_FRAGMENT);
}
但也许有更好的办法……
反应式方式:
Observable.from(getSupportFragmentManager().getFragments())
.filter(fragment -> fragment.isVisible())
.subscribe(fragment1 -> {
// Do something with it
}, throwable1 -> {
//
});
如果您正在使用Jetpack导航库:
val currentFragment = defaultNavigator.currentDestination
有点晚了，但有兴趣的人 如果你知道你想要的片段在FragmentManager中的索引，只需获得它的引用并检查isMenuVisible()函数!在这里:
getSupportFragmentManager().getFragments().get(0).isMenuVisible()
如果为真，它对用户可见，等等!
在SupportFragmentManager中有一个叫做findFragmentById()的方法。我在活动容器中使用它，就像:
public Fragment currentFragment(){
return getSupportFragmentManager().findFragmentById(R.id.activity_newsfeed_frame);
}
这就是如何获得当前的碎片。如果你有自定义片段，需要检查它是什么片段，我通常使用instanceof:
if (currentFragment() instanceof MyFrag){
// Do something here
}
