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
下面是一个Kotlin解决方案:
if ( this.getSupportFragmentManager().getBackStackEntryCount()>0 ) {
var fgmt = this.getSupportFragmentManager().fragments[this.getSupportFragmentManager().getBackStackEntryCount()-1]
if( fgmt is FgmtClassName ) {
(fgmt as FgmtClassName).doSth()
}
}
简化的方法:
with ( this.getSupportFragmentManager() ) {
if ( getBackStackEntryCount()>0 ) {
var fgmt = fragments[getBackStackEntryCount()-1]
if ( fgmt is FgmtClassName ) {
(fgmt as FgmtClassName).doSth()
}
}
}
其他回答
如果getFragmentManager()不工作，然后尝试与getSupportFragmentManager()，并在加载片段时添加一个标签。
public void onBackPressed(){
Fragment fragment=getSupportFragmentManager().findFragmentByTag(/*enter your tag*/);
if(fragment!=null && fragment.isVisible())
{
//do your code here
}
else
{
//do your code here
}
}
这是最好的方法:
android.app.Fragment currentFragment=getFragmentManager().findFragmentById(R.id.main_container);
if(currentFragment!=null)
{
String[] currentFragmentName = currentFragment.toString().split("\\{");
if (currentFragmentName[0].toString().equalsIgnoreCase("HomeSubjectFragment"))
{
fragment = new HomeStagesFragment();
tx = getSupportFragmentManager().beginTransaction();
tx.replace(R.id.main_container, fragment);
tx.addToBackStack(null);
tx.commit();
}
else if(currentFragmentName[0].toString().equalsIgnoreCase("HomeStagesFragment"))
{
new AlertDialog.Builder(this)
.setMessage("Are you sure you want to exit?")
.setCancelable(false)
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
finish();
}
})
.setNegativeButton("No", null)
.show();
}
}
不要忘记在header中定义这个:
private Fragment fragment;
FragmentTransaction tx;
也许最简单的方法是:
public MyFragment getVisibleFragment(){
FragmentManager fragmentManager = MainActivity.this.getSupportFragmentManager();
List<Fragment> fragments = fragmentManager.getFragments();
for(Fragment fragment : fragments){
if(fragment != null && fragment.getUserVisibleHint())
return (MyFragment)fragment;
}
return null;
}
这对我很有效
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。
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.
