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

请尝试这种方法.....

private Fragment getCurrentFragment(){
    FragmentManager fragmentManager = getSupportFragmentManager();
    String fragmentTag = fragmentManager.getBackStackEntryAt(fragmentManager.getBackStackEntryCount() - 1).getName();
    Fragment currentFragment = getSupportFragmentManager()
.findFragmentByTag(fragmentTag);
    return currentFragment;
}

其他回答

我最近不得不这样做,这里没有一个答案真正适合这种情况。

如果你确信只有一个片段是可见的(全屏),那么真的要找到backstack顶部的内容。例如,作为Fragment的Kotlin:

import androidx.fragment.app.Fragment

fun Fragment.setVisibilityChangeListener(clazz: Class<out Fragment>, listener: (Boolean) -> Unit) {
    fragmentManager?.run {
        addOnBackStackChangedListener {
            val topFragmentTag = getBackStackEntryAt(backStackEntryCount - 1).name
            val topFragment = findFragmentByTag(topFragmentTag)
            listener(topFragment != null && topFragment::class.java == clazz)
        }
    }
}

像这样使用它:

class MyFragment: Fragment {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        setVisibilityChangeListener(this::class.java) { visible -> 
            // Do stuff
        }
    }
}

〇应该可以

val visibleFragment = supportFragmentManager.fragments.findLast { fgm -> fgm.isVisible }
Timber.d("backStackIterator: visibleFragment: $visibleFragment")

您可以使用以下代码获取当前片段

FragmentClass f = (FragmentClass)viewPager.getAdapter().instantiateItem(viewPager, viewPager.getCurrentItem());

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.

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;