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
你也可以很容易地在logcat中使用URL，它将重定向到当前片段源代码的源代码。首先，你需要在主机活动中添加一个OnBackStackChangedListener，比如-
activity.getChildFragmentManager().addOnBackStackChangedListener(backStackListener);
OnBackStackChangedListener的实现是-
public FragmentManager.OnBackStackChangedListener backStackListener = () -> {
String simpleName = "";
String stackName = getStackTopName().trim();
if (Validator.isValid(stackName) && stackName.length() > 0) {
simpleName = stackName.substring(Objects.requireNonNull(stackName).lastIndexOf('.') + 1).trim();
List<Fragment >
fragmentList = getChildFragmentManager().getFragments();
Fragment myCurrentFragment;
for (int i = 0; i < fragmentList.size(); i++) {
myCurrentFragment= fragmentList.get(i);
if (myCurrentFragment.getClass().getSimpleName().equals(simpleName)) {
//Now you get the current displaying fragment assigned in myCurrentFragment.
break;
}
myFragment = null;
}
}
//The code below is for the source code redirectable logcat which would be optional for you.
StackTraceElement stackTraceElement = new StackTraceElement(simpleName, "", simpleName + ".java", 50);
String fileName = stackTraceElement.getFileName();
if (fileName == null) fileName = "";
final String info = "Current Fragment is:" + "(" + fileName + ":" +
stackTraceElement.getLineNumber() + ")";
Log.d("now", info + "\n\n");
};
getStackTopName()方法是-
public String getStackTopName() {
FragmentManager.BackStackEntry backEntry = null;
FragmentManager fragmentManager = getChildFragmentManager();
if (fragmentManager != null) {
if (getChildFragmentManager().getBackStackEntryCount() > 0)
backEntry = getChildFragmentManager().getBackStackEntryAt(
getChildFragmentManager().getBackStackEntryCount() - 1
);
}
return backEntry != null ? backEntry.getName() : null;
}
其他回答
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
}
如果您使用支持库v13，则此问题已修复，您应该简单地覆盖:
@Override
public void setUserVisibleHint(boolean isVisibleToUser)
{
// TODO Auto-generated method stub
super.setUserVisibleHint(isVisibleToUser);
}
问题是，你不能将两者混合，因为fragment与版本4的fragment类不兼容。
如果不是，并且您正在使用V4支持库，则将setPrimaryItem方法覆盖到FragmentStatePagerAdapter。
我用这个在大列表中更新Actionbat标题。
getSupportFragmentManager().findFragmentById(R.id.content_frame).getClass().getSimpleName();
我想这是对这个问题最直接的回答。 我希望这能有所帮助。
这样比暴露在这里更安全
supportFragmentManager.fragments.lastOrNull()?.let { currentFragment ->
//Do something here
}
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.
