Android 使用Navigation重复创建fragment，引起EventBus多次响应

移动开发 2023-05-05 05:23:32 阅读次数: 0

场景：MainActivity中有多个页面，并且每次EventBus会响应两次。经过多次尝试，有两个地方需要注意：

一、

EventBus增加注册和取消的判断，避免重复注册。

二、官方文档中将EventBus的注册和取消分别放在onCreate()和onDestroy方法中。经过多次测试发现，当onDestroy方法未调用时，新页面重新注册EventBus，会引起多次响应。

现在修改如下：

 @Override
    public void onStart() {
        super.onStart();
        if (!EventBus.getDefault().isRegistered(this)) {//加上判断
            EventBus.getDefault().register(this);
        }
    }

    @Override
    public void onStop() {
        super.onStop();
        if (EventBus.getDefault().isRegistered(this)) {
            EventBus.getDefault().unregister(this);
        }
    }

本以为问题得到解决，运行发现首页Fragment中onMessageEvent依旧会响应两次，但是其他页面并没有出现这种情况。

初步猜测：首页Fragment经过多次创建，导致多次触发onMessageEvent。

主页面采用Navigation管理fragment，并且自定义FragmentNavigator后，只有第一次打开主页面创建fragment，并没有重复创建fragment。

分别在HomeFragment和MeFragment的onCreate()方法中打印Log，灵异的事情发生了。

 没错，HomeFragment竟然创建两次。点击切换MeFragment……

 发现MeFragment创建一次。那么可以肯定，问题出现在HomeFragment身上，经过排查却没有任何发现，于是将目光再次转移到自定义FragmentNavigator。

自定义Navigation

@Navigator.Name("fixFragment") //这是新的Navigator得名称,千万别忘了加
public class FixFragmentNavigator extends FragmentNavigator {
    private final String TAG = "ReLoadFragmentNavictor";
    private final Context mContext;
    private final FragmentManager mFragmentManager;
    private final int mContainerId;
  

    public FixFragmentNavigator(@NonNull Context context, @NonNull FragmentManager manager, int containerId) {
        super(context, manager, containerId);
        mContext = context;
        mFragmentManager = manager;
        mContainerId = containerId;
    }

    @Nullable
    @Override
    public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args, @Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {

        if (mFragmentManager.isStateSaved()) {
            Log.i(TAG, "Ignoring navigate() call: FragmentManager has already"
                    + " saved its state");
            return null;
        }
        String className = destination.getClassName();
        if (className.charAt(0) == '.') {
            className = mContext.getPackageName() + className;
        }
        final FragmentTransaction ft = mFragmentManager.beginTransaction();


        int enterAnim = navOptions != null ? navOptions.getEnterAnim() : -1;
        int exitAnim = navOptions != null ? navOptions.getExitAnim() : -1;
        int popEnterAnim = navOptions != null ? navOptions.getPopEnterAnim() : -1;
        int popExitAnim = navOptions != null ? navOptions.getPopExitAnim() : -1;
        if (enterAnim != -1 || exitAnim != -1 || popEnterAnim != -1 || popExitAnim != -1) {
            enterAnim = enterAnim != -1 ? enterAnim : 0;
            exitAnim = exitAnim != -1 ? exitAnim : 0;
            popEnterAnim = popEnterAnim != -1 ? popEnterAnim : 0;
            popExitAnim = popExitAnim != -1 ? popExitAnim : 0;
            ft.setCustomAnimations(enterAnim, exitAnim, popEnterAnim, popExitAnim);
        }

        Fragment fragment = mFragmentManager.getPrimaryNavigationFragment();

        if (fragment != null) {
            ft.hide(fragment);
        }
        Fragment frag = null;
        String tag = String.valueOf(destination.getId());
        frag = mFragmentManager.findFragmentByTag(tag);
        Log.e("TAG_frag",className+"====="+(null == frag));

        if (frag != null) {
            ft.show(frag);
        } else {
            
            frag = instantiateFragment(mContext, mFragmentManager,
                        className, args);
            frag.setArguments(args);
            ft.add(mContainerId, frag, tag);
           
        }
        ft.setPrimaryNavigationFragment(frag);

        final @IdRes int destId = destination.getId();

        //通过反射获取mBackStack
        ArrayDeque<Integer> mBackStack;
        try {
            Field field = FragmentNavigator.class.getDeclaredField("mBackStack");
            field.setAccessible(true);
            mBackStack = (ArrayDeque<Integer>) field.get(this);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }

        final boolean initialNavigation = mBackStack.isEmpty();
        final boolean isSingleTopReplacement = navOptions != null && !initialNavigation
                && navOptions.shouldLaunchSingleTop()
                && mBackStack.peekLast() == destId;

        boolean isAdded;
        if (initialNavigation) {
            isAdded = true;
        } else if (isSingleTopReplacement) {
            if (mBackStack.size() > 1) {
                mFragmentManager.popBackStack(
                        generateBackStackName(mBackStack.size(), mBackStack.peekLast()),
                        FragmentManager.POP_BACK_STACK_INCLUSIVE);
                ft.addToBackStack(generateBackStackName(mBackStack.size(), destId));
            }
            isAdded = false;
        } else {
            ft.addToBackStack(generateBackStackName(mBackStack.size() + 1, destId));
            isAdded = true;
        }
        if (navigatorExtras instanceof Extras) {
            Extras extras = (Extras) navigatorExtras;
            for (Map.Entry<View, String> sharedElement : extras.getSharedElements().entrySet()) {
                ft.addSharedElement(sharedElement.getKey(), sharedElement.getValue());
            }
        }
        ft.setReorderingAllowed(true);
        ft.commit();
        if (isAdded) {
            mBackStack.add(destId);
            return destination;
        } else {
            return null;
        }
    }
    //navigate需要打方法重复类直接复制过来就可以
    @NonNull
    private String generateBackStackName(int backStackIndex, int destId) {
        return backStackIndex + "-" + destId;
    }
}

打印日志发现，

frag = mFragmentManager.findFragmentByTag(tag);

获取tag为空，导致HomeFragment被创建两次，这就很奇怪了。

 经过多方验证，

ft.commit();提交后，并未立即生效。如果短时间内重新创建fragment，并不会获取到tag。

既然知道问题出在哪儿，事情就好办了。最简单的方法——增加临时标志oldClassName。

 if (frag != null) {
            ft.show(frag);
        } else {
            if (!className.equals(oldClassName)){
                oldClassName = className;
                frag = instantiateFragment(mContext, mFragmentManager,
                        className, args);
                frag.setArguments(args);
                ft.add(mContainerId, frag, tag);
            }

        }

——————————————问题解决，附带其他代码————————————————

第二部，设置NavController:

  Fragment fragmentById = getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
        //fragment的重复加载问题和NavController有关
        navController = NavHostFragment.findNavController(fragmentById);

        NavigatorProvider provider = navController.getNavigatorProvider();
        //设置自定义的navigator
        FixFragmentNavigator fixFragmentNavictor = new FixFragmentNavigator(this, fragmentById.getChildFragmentManager(), fragmentById.getId());
        provider.addNavigator(fixFragmentNavictor);

        NavGraph navDestinations = initNavGraph(provider, fixFragmentNavictor);
        navController.setGraph(navDestinations);

第三步，去除xml容器中navGraph属性:app:navGraph="@navigation/navigation" 

  <androidx.fragment.app.FragmentContainerView
            android:id="@+id/nav_host_fragment"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            app:defaultNavHost="false"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:navGraph="@navigation/navigation" ///这一行去除
            />

第四步，创建新navGraph

private NavGraph initNavGraph(NavigatorProvider provider, FixFragmentNavigator fragmentNavigator) {
        NavGraph navGraph = new NavGraph(new NavGraphNavigator(provider));

        //用自定义的导航器来创建目的地
        FragmentNavigator.Destination destination1 = fragmentNavigator.createDestination();
        destination1.setId(R.id.nav_message);
        destination1.setClassName(MessagesFragment.class.getCanonicalName());
        navGraph.addDestination(destination1);


        FragmentNavigator.Destination destination2 = fragmentNavigator.createDestination();
        destination2.setId(R.id.nav_work);
        destination2.setClassName(WorkFragment.class.getCanonicalName());
        navGraph.addDestination(destination2);

        FragmentNavigator.Destination destination3 = fragmentNavigator.createDestination();
        destination3.setId(R.id.nav_contacts);
        destination3.setClassName(ContactsFragment.class.getCanonicalName());
        navGraph.addDestination(destination3);

        FragmentNavigator.Destination destination4 = fragmentNavigator.createDestination();
        destination4.setId(R.id.nav_me);
        destination4.setClassName(MeFragment.class.getCanonicalName());
        navGraph.addDestination(destination4);

        FragmentNavigator.Destination destination5 = fragmentNavigator.createDestination();
        destination5.setId(R.id.nav_usersmessages);
        destination5.setClassName(UsersMessagesFragment.class.getCanonicalName());
        navGraph.addDestination(destination5);

        navGraph.setStartDestination(destination1.getId());

        return navGraph;
    }

第五步，关联点击事件
       NavigationUI.setupWithNavController(activityIndexBinding.navBottom,navController);
        //正确的关联方式o(￣▽￣)ｄ
        activityIndexBinding.navBottom.setOnNavigationItemSelectedListener(item -> {

            //切换布局关键代码
            navController.navigate(item.getItemId());
            return true;
        });

我没有使用NavigationUI，而是自定义的选项卡。

public class MainTabIndicator extends LinearLayout {

    private int i = 0;

    public MainTabIndicator(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public void addTab(View tabView) {

        tabView.setTag(i++);
        tabView.setOnClickListener(mClickListener);
        addView(tabView, new LayoutParams(0, MATCH_PARENT, 1));
    }
    private View mTabView;
    private OnClickListener mClickListener = new OnClickListener() {
        @Override
        public void onClick(View v) {
            if (v == null){
                return;
            }
            Object tag = v.getTag();
            if (tag instanceof Integer){
                int index = (int) tag;
                if (lisener != null ){
                    lisener.onTabSelected(index);
                    if (mTabView != null) {
                        if (mTabView.equals(v))
                            return;
                        mTabView.setSelected(false);
                    }
                    v.setSelected(true);
                    mTabView = v;
                }
            }

        }
    };

    public void setCurrentTab(int index) {
        mClickListener.onClick(getChildAt(index));
    }

    OnChangeLisener lisener;
    public void setOnChangeLisener( OnChangeLisener lisener){
        this.lisener = lisener;
    }
    public interface OnChangeLisener {
        public void onTabSelected(int position);
    }
}

使用方式，修改为自定义view包名

 <com.xxx.view.MainTabIndicator
        android:id="@+id/bottom_navigation_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/white" />

实例化后，可以根据需求添加图文和文字，或者单图。

tabPageIndicator.addTab(getIndicator(R.drawable.icon_tab_home, R.string.below_button_home));
tabPageIndicator.addView(getIndicator(R.mipmap.call_phone), new LinearLayout.LayoutParams(0, MATCH_PARENT, 1));
tabPageIndicator.addTab(getIndicator(R.drawable.icon_tab_me, R.string.below_button_me));

增加监听和默认选中

 tabPageIndicator.setOnChangeLisener(this);
 tabPageIndicator.setCurrentTab(0);

以下为全部代码

 private void initTabBar() {
        tabPageIndicator = (MainTabIndicator) findViewById(R.id.bottom_navigation_bar);
        tabPageIndicator.removeAllViews();
        tabPageIndicator.addTab(getIndicator(R.drawable.icon_tab_home, R.string.below_button_home));
        tabPageIndicator.addView(getIndicator(R.mipmap.call_phone), new LinearLayout.LayoutParams(0, MATCH_PARENT, 1));
        tabPageIndicator.addTab(getIndicator(R.drawable.icon_tab_me, R.string.below_button_me));

        tabPageIndicator.setOnChangeLisener(this);
        tabPageIndicator.setCurrentTab(0);

    }

——————————————撒花庆祝————————————————

补充：偶然间发现，MainActivity使用Navigation，切换到权限管理，更改权限后【联系人权限、悬浮窗权限】，会引起闪退【不同权限都尝试一下，有的权限更改并不会引起闪退】。

androidx.navigation.fragment.NavHostFragment did not create a view.

修改代码：

@Navigator.Name("fixFragment") //这是新的Navigator得名称,千万别忘了加
public class FixFragmentNavigator extends FragmentNavigator {
    private final String TAG = "ReLoadFragmentNavictor";
    private final Context mContext;
    private final FragmentManager mFragmentManager;
    private final int mContainerId;
    String oldClassName = null;

    public FixFragmentNavigator(@NonNull Context context, @NonNull FragmentManager manager, int containerId) {
        super(context, manager, containerId);
        mContext = context;
        mFragmentManager = manager;
        mContainerId = containerId;
    }

    @Nullable
    @Override
    public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args, @Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {

        if (mFragmentManager.isStateSaved()) {
            Log.i(TAG, "Ignoring navigate() call: FragmentManager has already"
                    + " saved its state");
            return null;
        }
        String className = destination.getClassName();
        if (className.equals(oldClassName)){
            return null;
        }
        oldClassName = className;
        if (className.charAt(0) == '.') {
            className = mContext.getPackageName() + className;
        }
        Fragment frag = mFragmentManager.findFragmentByTag(className);
        if (null == frag) {
            //不存在，则创建
            frag = instantiateFragment(mContext, mFragmentManager, className, args);

        }

        frag.setArguments(args);
        final FragmentTransaction ft = mFragmentManager.beginTransaction();

        int enterAnim = navOptions != null ? navOptions.getEnterAnim() : -1;
        int exitAnim = navOptions != null ? navOptions.getExitAnim() : -1;
        int popEnterAnim = navOptions != null ? navOptions.getPopEnterAnim() : -1;
        int popExitAnim = navOptions != null ? navOptions.getPopExitAnim() : -1;
        if (enterAnim != -1 || exitAnim != -1 || popEnterAnim != -1 || popExitAnim != -1) {
            enterAnim = enterAnim != -1 ? enterAnim : 0;
            exitAnim = exitAnim != -1 ? exitAnim : 0;
            popEnterAnim = popEnterAnim != -1 ? popEnterAnim : 0;
            popExitAnim = popExitAnim != -1 ? popExitAnim : 0;
            ft.setCustomAnimations(enterAnim, exitAnim, popEnterAnim, popExitAnim);
        }

//        ft.replace(mContainerId, frag);
        List<Fragment> fragments = mFragmentManager.getFragments();
        for (Fragment fragment : fragments) {
            ft.hide(fragment);
        }
        if (!frag.isAdded()) {
            ft.add(mContainerId, frag, className);
        }

        ft.show(frag);
        ft.setPrimaryNavigationFragment(frag);

        final @IdRes int destId = destination.getId();

        //通过反射获取mBackStack
        ArrayDeque<Integer> mBackStack;
        try {
            Field field = FragmentNavigator.class.getDeclaredField("mBackStack");
            field.setAccessible(true);
            mBackStack = (ArrayDeque<Integer>) field.get(this);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }

        final boolean initialNavigation = mBackStack.isEmpty();
        final boolean isSingleTopReplacement = navOptions != null && !initialNavigation
                && navOptions.shouldLaunchSingleTop()
                && mBackStack.peekLast() == destId;

        boolean isAdded;
        if (initialNavigation) {
            isAdded = true;
        } else if (isSingleTopReplacement) {
            if (mBackStack.size() > 1) {
                mFragmentManager.popBackStack(
                        generateBackStackName(mBackStack.size(), mBackStack.peekLast()),
                        FragmentManager.POP_BACK_STACK_INCLUSIVE);
                ft.addToBackStack(generateBackStackName(mBackStack.size(), destId));
            }
            isAdded = false;
        } else {
            ft.addToBackStack(generateBackStackName(mBackStack.size() + 1, destId));
            isAdded = true;
        }
        if (navigatorExtras instanceof Extras) {
            Extras extras = (Extras) navigatorExtras;
            for (Map.Entry<View, String> sharedElement : extras.getSharedElements().entrySet()) {
                ft.addSharedElement(sharedElement.getKey(), sharedElement.getValue());
            }
        }
        ft.setReorderingAllowed(true);
        ft.commit();
        if (isAdded) {
            mBackStack.add(destId);
            return destination;
        } else {
            return null;
        }
    }
    //navigate需要打方法重复类直接复制过来就可以
    @NonNull
    private String generateBackStackName(int backStackIndex, int destId) {
        return backStackIndex + "-" + destId;
    }
}

——————————————再次撒花庆祝————————————————

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