63

以下是我选择的底部导航视图项的代码

bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {  
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    Fragment fragment = null;
    switch (item.getItemId()) {
        case R.id.action_one:
            // Switch to page one
            fragment = FragmentA.newInstance();
            break;
        case R.id.action_two:
            // Switch to page two
            fragment = FragmentB.newInstance();
            break;
        case R.id.action_three:
            // Switch to page three
            fragment = FragmentC.newInstance();
            break;
    }
    getSupportFragmentManager().beginTransaction().replace(R.id.container,fragment,"TAG").commit();
    return true;
}
});

现在我的问题是每次重新创建片段并且不希望每次我也尝试添加 addToBackStack(null) 时都重新创建片段，但是这种情况下按下后退按钮会不断从堆栈中弹出我不想要的片段。

有没有办法在选择的底部导航栏上显示片段而不重新创建片段

4

16 回答 16

26

使用支持库 v26，您可以做到这一点

FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();

Fragment curFrag = mFragmentManager.getPrimaryNavigationFragment();
if (curFrag != null) {
    fragmentTransaction.detach(curFrag);
}

Fragment fragment = mFragmentManager.findFragmentByTag(tag);
if (fragment == null) {
    fragment = new YourFragment();
    fragmentTransaction.add(container.getId(), fragment, tag);
} else {
    fragmentTransaction.attach(fragment);
}

fragmentTransaction.setPrimaryNavigationFragment(fragment);
fragmentTransaction.setReorderingAllowed(true);
fragmentTransaction.commitNowAllowingStateLoss();
于 2017-07-25T10:48:18.003 回答
16

我遇到了同样的问题，最后我找到了解决方案，你可以试试这个代码。这对我有用。

import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.widget.FrameLayout;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
public BottomNavigationView bv;
public home_fragment home;
public account_fragment afrag;
public other_fragment other;
public FrameLayout fr;
android.support.v4.app.Fragment current;
//public FragmentTransaction frt;
    public static int temp=0;
    final Fragment fragment11 = new account_fragment();
    final Fragment fragment22 = new home_fragment();
    final Fragment fragment33 = new other_fragment();
    final FragmentManager fm = getSupportFragmentManager();
    Fragment active = fragment11;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bv=(BottomNavigationView) findViewById(R.id.navigationView);


        fm.beginTransaction().add(R.id.main_frame, fragment33, "3").hide(fragment33).commit();
        fm.beginTransaction().add(R.id.main_frame, fragment22, "2").hide(fragment22).commit();
        fm.beginTransaction().add(R.id.main_frame,fragment11, "1").commit();
bv.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {

            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.account:
                        fm.beginTransaction().hide(active).show(fragment11).commit();
                        active = fragment11;
                        return true;

                    case R.id.home1:
                        fm.beginTransaction().hide(active).show(fragment22).commit();
                        active = fragment22;
                        return true;

                    case R.id.other:
                        fm.beginTransaction().hide(active).show(fragment33).commit();
                        active = fragment33;
                        return true;
                }
                return false;
            }
        });
      bv.setOnNavigationItemReselectedListener(new BottomNavigationView.OnNavigationItemReselectedListener() {
          @Override
          public void onNavigationItemReselected(@NonNull MenuItem item) {
              Toast.makeText(MainActivity.this, "Reselected", Toast.LENGTH_SHORT).show();

          }
      });


    }

}
于 2018-09-06T22:56:58.233 回答
15

这似乎对我很有效。我没有附加和分离，而是使用显示或隐藏来维护片段状态。

    public void changeFragment(Fragment fragment, String tagFragmentName) {

        FragmentManager mFragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();

        Fragment currentFragment = mFragmentManager.getPrimaryNavigationFragment();
        if (currentFragment != null) {
            fragmentTransaction.hide(currentFragment);
        }

        Fragment fragmentTemp = mFragmentManager.findFragmentByTag(tagFragmentName);
        if (fragmentTemp == null) {
            fragmentTemp = fragment;
            fragmentTransaction.add(R.id.frame_layout, fragmentTemp, tagFragmentName);
        } else {
            fragmentTransaction.show(fragmentTemp);
        }

        fragmentTransaction.setPrimaryNavigationFragment(fragmentTemp);
        fragmentTransaction.setReorderingAllowed(true);
        fragmentTransaction.commitNowAllowingStateLoss();
    }

这就是我使用它的方式

     private void initViews() {
        BottomNavigationView bottomNavigationView = findViewById(R.id.navigation);
        bottomNavigationView.setOnNavigationItemSelectedListener
                (new BottomNavigationView.OnNavigationItemSelectedListener() {
                    @Override
                    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                        Fragment selectedFragment = null;
                        switch (item.getItemId()) {
                            case R.id.explore:
                                changeFragment(new ExploreFragment(), ExploreFragment.class
                                        .getSimpleName());
                                toggleViews(true, "");
                                break;
                            case R.id.favorite:
                                changeFragment(new FavoriteFragment(), FavoriteFragment.class
                                        .getSimpleName());
                                toggleViews(false, "Favorites");
                                break;
                            case R.id.venue:
                                changeFragment(new VenueFragment(), VenueFragment.class.getSimpleName());
                                toggleViews(false, "Venues");
                                break;
                            case R.id.profile:
                                changeFragment(new ProfileFragment(), ProfileFragment.class
                                        .getSimpleName());
                                toggleViews(false, "Profile");
                                break;
                        }
                        return true;
                    }
                });

        //Manually displaying the first fragment - one time only
        changeFragment(new ExploreFragment(), ExploreFragment.class
                .getSimpleName());

    }
于 2018-11-08T08:20:51.740 回答
12

当再次单击当前选定的导航按钮时，此解决方案会阻止重新创建片段。但是，每次用户单击不同的导航按钮时，都会创建一个新片段。

Fragment只需添加此行以避免重新创建BottomNavigationView

 bottomNavigation.setOnNavigationItemReselectedListener(new BottomNavigationView.OnNavigationItemReselectedListener() {
            @Override
            public void onNavigationItemReselected(@NonNull MenuItem item) {
             // do nothing here   
            }
        });

或者使用 lambda：

bottomNavigation.setOnNavigationItemReselectedListener(item -> { });
于 2020-03-02T06:42:56.193 回答
8

使用时要小心replace。即使提供已经存在于内存中的片段，replace也会重新启动片段的生命周期。为避免重新启动，事务对象的方法包括add、show和hide，可用于显示正确的片段而无需重新启动它。

private fun switchFragment(selectedTabIndex: Int) {
    val previousTabIndex = this.currentTabIndex
    this.currentTabIndex = selectedTabIndex

    val transaction = supportFragmentManager.beginTransaction()
    val tag = fragments[this.currentTabIndex].tag

    // if the fragment has not yet been added to the container, add it first
    if (supportFragmentManager.findFragmentByTag(tag) == null) {
        transaction.add(R.id.container, fragments[this.currentTabIndex], tag)
    }

    transaction.hide(fragments[previousTabIndex])
    transaction.show(fragments[this.currentTabIndex])
    transaction.commit()
}
于 2017-08-09T15:35:18.757 回答
7

尝试这个 ：

bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
                @Override
                public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                    Fragment fragment = null;
                    Fragment currentFragment = getSupportFragmentManager().findFragmentById(R.id.container);
                    switch (item.getItemId()) {
                        case R.id.action_one:
                            // Switch to page one
                            if (!(currentFragment instanceof FragmentA)) {
                                fragment = FragmentA.newInstance();
                            }
                            break;
                        case R.id.action_two:
                            // Switch to page two
                            if (!(currentFragment instanceof FragmentB)) {
                                fragment = FragmentB.newInstance();
                            }
                            break;
                        case R.id.action_three:
                            // Switch to page three
                            if (!(currentFragment instanceof FragmentC)) {
                                fragment = FragmentC.newInstance();
                            }
                            break;
                    }
                    getSupportFragmentManager().beginTransaction().replace(R.id.container, fragment, "TAG").commit();
                    return true;
                }
            });

这将获得当前片段，container如果您再次单击该片段，则不会重新添加该片段。

于 2017-02-21T10:35:54.117 回答
7

setOnNavigationItemReselectedListener 将是一个更好的解决方案

于 2017-06-02T10:44:23.647 回答
4

像这样使用 setOnNavigationItemReselectedListener：

private BottomNavigationView.OnNavigationItemReselectedListener onNavigationItemReselectedListener
            = new BottomNavigationView.OnNavigationItemReselectedListener() {

        @Override
        public void onNavigationItemReselected(@NonNull MenuItem item) {
            Toast.makeText(MainActivity.this, "Reselected", Toast.LENGTH_SHORT).show();
        }
    };

并使用以下方法调用它：

navigation.setOnNavigationItemReselectedListener(onNavigationItemReselectedListener);
于 2017-12-03T16:55:33.873 回答
2

我发现最好的方法。

private void replace_fragment(Fragment fragment) {

        String tag = fragment.getClass().getSimpleName();
        FragmentTransaction tr = getSupportFragmentManager().beginTransaction();

        Fragment curFrag = getSupportFragmentManager().getPrimaryNavigationFragment();
        Fragment cacheFrag = getSupportFragmentManager().findFragmentByTag(tag);

        if (curFrag != null)
            tr.hide(curFrag);

        if (cacheFrag == null) {
            tr.add(R.id.main_frame, fragment, tag);
        } else {
            tr.show(cacheFrag);
            fragment = cacheFrag;
        }

        tr.setPrimaryNavigationFragment(fragment);
        tr.commit();

    }

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {

            switch (item.getItemId()) {
                case R.id.nav_posts:
                    replace_fragment(new PostsFragment());
                    return true;
                case R.id.nav_stores:
                    replace_fragment(new StoresFragment());
                    return true;
                case R.id.nav_chats:
                    replace_fragment(new DiscussionsFragment());
                    return true;
                case R.id.nav_account:
                    replace_fragment(new ProfileFragment());
                    return true;
            }
            return false;
        }
    };
于 2019-12-20T10:48:31.333 回答
1

我通过添加一个ViewPager我将所有导航片段委托给它来解决这个问题。当FragmentPagerAdapter用户浏览BotoomNavigationView.

为此，您必须完成 5 个简单的步骤：

  1. ViewPager在您的布局中添加一个；

  2. 实现它的适配器：

    class YourNavigationViewPagerAdapter(fm: FragmentManager,
                                     private val param1: Int,
                                     private val param2: Int)

    : FragmentPagerAdapter(fm) {

    override fun getItem(p0: Int) = when(p0) {
        0 -> NavigationFragment1.newInstance(param1, param2)
        1 -> NavigationFragment2.newInstance(param1, param2)
        2 -> NavigationFragment3.newInstance(param1, param2)
        else -> null
    }

    override fun getCount() = 3
}

  3. 不要忘记设置新的适配器：

    yourViewPager.adapter = YourNavigationViewPagerAdapter(supportFragmentManager, param1, param2)

  4. 将 a 设置OnNavigationItemSelectedListener为您BottomNavigationView的以下内容：

    yourBottomNavigationView.setOnNavigationItemSelectedListener {

    when(it.itemId) {

        R.id.yourFirstFragmentMenuItem -> {
            yourViewPager.currentItem = 0
            true
        }

        R.id.yourSecondFragmentMenuItem -> {
            yourViewPager.currentItem = 1
            true
        }

        R.id.yourThirdFragmentMenuItem -> {
            yourViewPager.currentItem = 2
            true
        }


        else -> false
    }
}

  5. 将 a 设置OnPageChangeListener为您ViewPager的以下内容：

    yourViewPager.addOnPageChangeListener(object : 
ViewPager.OnPageChangeListener {
    override fun onPageScrollStateChanged(p0: Int) {

    }

    override fun onPageScrolled(p0: Int, p1: Float, p2: Int) {

    }

    override fun onPageSelected(p0: Int) {
        yourBottomNavigationView.menu.getItem(p0).isChecked = true
    }

})

  6. 请享用 ：）

于 2018-11-03T16:13:34.343 回答
1

我改进了@Viven 的答案并用 Kotlin 编写。我的版本仅第一次实例化片段，隐藏/显示。我是 Kotlin 的新手，所以请告诉我是否可以改进。

我们需要持有一个 id 来标记地图：

private val fragmentTags = hashMapOf(
        R.id.action_home to "home_fragment",
        R.id.action_profile to "profile_fragment"
)

监听器代码：

bottomNavigation.run {
    setOnNavigationItemSelectedListener { menuItem ->
        supportFragmentManager.beginTransaction()
                .let { transaction ->
                    // hide current fragment
                    supportFragmentManager.primaryNavigationFragment?.let {
                        // if selected fragment's tag is same, do nothing.
                        if (it.tag == fragmentTags[menuItem.itemId]) {
                            return@setOnNavigationItemSelectedListener true
                        }

                        transaction.hide(it)
                    }

                    var fragment  = supportFragmentManager.findFragmentByTag(fragmentTags[menuItem.itemId])

                    if (fragment == null) {
                        // instantiate fragment for the first time
                        fragment = when(menuItem.itemId) {
                            R.id.action_home -> HomeFragment()
                            R.id.action_profile -> ProfileFragment()
                            else -> null
                        }?.also {
                            // and add it 
                            transaction.add(R.id.frame, it, fragmentTags[menuItem.itemId])
                        }
                    } else {
                        // if it's found show it 
                        transaction.show(fragment)
                    }


                    transaction
                            .setPrimaryNavigationFragment(fragment)
                            .setReorderingAllowed(true)
                }.commitNowAllowingStateLoss()

        return@setOnNavigationItemSelectedListener true
    }

    //bottomNavigation things
    itemIconTintList = null
    selectedItemId = R.id.action_home
}
于 2018-09-22T17:48:41.390 回答
1

为此，我在 Kotlin 中编写了一个扩展函数。

fun FragmentManager.switch(containerId: Int, newFrag: Fragment, tag: String) {

var current = findFragmentByTag(tag)
beginTransaction()
    .apply {

        //Hide the current fragment
        primaryNavigationFragment?.let { hide(it) }

        //Check if current fragment exists in fragmentManager
        if (current == null) {
            current = newFrag
            add(containerId, current!!, tag)
        } else {
            show(current!!)
        }
    }
    .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
    .setPrimaryNavigationFragment(current)
    .setReorderingAllowed(true)
    .commitNowAllowingStateLoss()
}
于 2019-05-14T06:05:48.320 回答
0

使用 Cicerone 库轻松处理导航。

https://github.com/terrakok/Cicerone

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
    switch (menuItem.getItemId()) {
        case R.id.save: {
            router.replaceScreen("your fragment1");
            menuItem.setChecked(true);
            break;
        }
        case R.id.search_lessons: {
            router.replaceScreen("your fragment2");
            menuItem.setChecked(true);
            break;
        }
        case R.id.profile_student: {
            router.replaceScreen("your fragment3");
            menuItem.setChecked(true);
            break;
        }

    }
    return false;
}
于 2019-11-08T05:52:27.750 回答
0

如何使用 BottomNavigationView 在片段已经可见时停止重新创建片段

步骤1 - 

     @Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    Fragment fragment = null;
    String valuestring;      
    **if (item.getItemId() == lastSelectedItemId) { // added this
        Log.e( "both id is same","LULL" );
        return true;
    }**
    switch (item.getItemId()) {
       case R.id.navigation_category:
      SetActioBarText( getString( R.string.label_actionbar_categories ) );
            fragment = new CategoryFragment();
            valuestring = "category";
            break;
        case R.id.navigation_favourite:
     SetActioBarText( getString( R.string.label_actionbar_favourites ) );
            fragment = new FavouriteFragment();
            valuestring = "favourites";
            break;
        default:
            throw new IllegalStateException( "Unexpected value: " +                  menuItem.getItemId() );
    }
    return loadFragment( fragment, valuestring ,menuItem);
}

现在第2步---

    private boolean loadFragment(Fragment fragment, String argument,MenuItem item) {
  
    if (fragment != null) {
       
        transaction = fragmentManager.beginTransaction();
        transaction.addToBackStack( argument );
        transaction.setTransition( FragmentTransaction.TRANSIT_FRAGMENT_FADE );
        transaction.replace( R.id.frame_container, fragment,                         "demofragment").commitAllowingStateLoss();

     lastSelectedItemId= item.getItemId();
    
        return true;
    }
    return false;
}
于 2020-09-07T10:20:33.127 回答
0

正确导航涉及几个测试用例，我粘贴我的代码并检查所有测试用例。

FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        switch (item.getItemId()) {
            case R.id.dashboard:
                Fragment fragment;
                fragment = fragmentManager.findFragmentByTag(DashboardFragment.TAG);

                if (fragment == null) {
                    fragment = new DashboardFragment();
                    fragmentTransaction.add(R.id.frame, fragment, DashboardFragment.TAG);
                } else {
                    fragmentTransaction.detach(fragmentManager.getPrimaryNavigationFragment());
                    fragmentTransaction.attach(fragment);
                }
                fragmentTransaction.setPrimaryNavigationFragment(fragment);
                fragmentTransaction.commitNow();
                return true;
            case R.id.expenses:
                fragment = fragmentManager.findFragmentByTag(ExpenseFragment.TAG);
                if (fragment == null) {
                    fragment = new ExpenseFragment();
                    fragmentTransaction.add(R.id.frame, fragment, ExpenseFragment.TAG);
                } else {
                    fragmentTransaction.detach(fragmentManager.getPrimaryNavigationFragment());
                    fragmentTransaction.attach(fragment);
                }
                fragmentTransaction.setPrimaryNavigationFragment(fragment);
                fragmentTransaction.commitNow();
                return true;
            case R.id.vehicle_parts:
                Bundle bundle = new Bundle();
                bundle.putInt("odometer", vehicle.getOdometer());
                bundle.putString("vehicle_id", vehicle.get_id());
                fragment = fragmentManager.findFragmentByTag(PartsFragment.TAG);
                if (fragment == null) {
                    fragment = new PartsFragment();
                    fragment.setArguments(bundle);
                    fragmentTransaction.add(R.id.frame, fragment, PartsFragment.TAG);

                } else {
                    fragmentTransaction.detach(fragmentManager.getPrimaryNavigationFragment());
                    fragmentTransaction.attach(fragment);
                }
                fragmentTransaction.setPrimaryNavigationFragment(fragment);
                fragmentTransaction.commitNow();
                return true;
            case R.id.blog:
                fragment = fragmentManager.findFragmentByTag(BlogFragment.TAG);

                if (fragment == null) {
                    fragment = new BlogFragment();
                    fragmentTransaction.add(R.id.frame, fragment, BlogFragment.TAG);

                } else {
                    fragmentTransaction.detach(fragmentManager.getPrimaryNavigationFragment());
                    fragmentTransaction.attach(fragment);
                }
                fragmentTransaction.setPrimaryNavigationFragment(fragment);
                fragmentTransaction.commitNow();
                return true;
        }
        return false;
于 2018-06-06T06:34:08.173 回答
-1

不需要做这个答案。实际上，您真正需要的是在特定片段中保存视图。

 private   View view;
if(view == null){
    view = inflater.inflate(R.layout.call_fragment_edited, container, false);

}

所以任何时候当你创建新片段时，你都会看到当前状态

于 2020-12-13T08:55:43.377 回答