处理 Android 导航组件中的后退按钮

Question

我想知道如何使用导航控制器正确处理系统后退按钮操作。在我的应用程序中，我有两个片段（例如片段 1 和片段 2），我在片段 1 中有一个动作，目标是片段 2。除了一件事，一切都很好——当用户在 fragment2 中按下系统后退按钮时，我想显示一个对话框（例如使用 DialogFragment）来确认退出。实现此行为的最佳方法是什么？如果我在主机片段中使用 app:defaultNavHost="true"，那么它会自动返回并忽略我的规则。另外，这个组件是做什么用的？

我应该使用 "pop to" 吗？

Answer 1

这是一个应该做你想做的解决方案，但我认为这是一个糟糕的解决方案，因为它违背了 Android 导航组件的想法（让 android 处理导航）。

在您的 activity

中覆盖 "onBackPressed"

override fun onBackPressed() {
    when(NavHostFragment.findNavController(nav_host_fragment).currentDestination.id) {
        R.id.fragment2-> {
            val dialog=AlertDialog.Builder(this).setMessage("Hello").setPositiveButton("Ok", DialogInterface.OnClickListener { dialogInterface, i ->
                finish()
            }).show()
        }
        else -> {
            super.onBackPressed()
        }
    }
}

Answer 2

所以，我创建了一个界面

public interface OnBackPressedListener {
    void onBackPressed();
}

并由所有需要处理后退按钮的片段实现。在主要 activity 中，我重写了 onBackPressed() 方法：

@Override
public void onBackPressed() {
    final Fragment currentFragment = mNavHostFragment.getChildFragmentManager().getFragments().get(0);
    final NavController controller = Navigation.findNavController(this, R.id.nav_host_fragment);
    if (currentFragment instanceof OnBackPressedListener)
        ((OnBackPressedListener) currentFragment).onBackPressed();
    else if (!controller.popBackStack())
        finish();

}

因此，如果我的导航主机的顶部片段实现了 OnBackPressedListener 接口，我将调用它的 onBackPressed() 方法，在其他地方，如果返回堆栈为空，我只需弹出返回堆栈并关闭应用程序。

Answer 3

试试这个。我想这会对你有所帮助。

override fun onBackPressed() {
    when (mNavController.getCurrentDestination()!!.getId()) {

        R.id.loginFragment -> {
            onWarningAlertDialog(this, "Alert", "Do you want to close this application ?")
        }
        R.id.registerFragment -> {
            super.onBackPressed()
        }
    }
}



private fun onWarningAlertDialog(mainActivity: MainActivity, s: String, s1: String) {

        val dialogBuilder = AlertDialog.Builder(this)
        dialogBuilder.setMessage(/*""*/s1)
                .setCancelable(false)
                .setPositiveButton("Proceed", DialogInterface.OnClickListener { dialog, id ->
                    finish()
                })
                .setNegativeButton("Cancel", DialogInterface.OnClickListener { dialog, id ->
                    dialog.cancel()
                })

        // create dialog box
        val alert = dialogBuilder.create()
        // set title for alert dialog box
        alert.setTitle("AlertDialogExample")
        // show alert dialog
        alert.show()
    }

Answer 4

更新 21 年 4 月 22 日

我正在更新我的答案以展示推荐方法的示例，该方法也在上面。

class MyFragment : Fragment() {

    ...
    
    private val backPressedDispatcher = object : OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            // Redirect to our own function
            this@MyFragment.onBackPressed()
        }
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        ...

        setHasOptionsMenu(true) //Set this to true in order to trigger callbacks to Fragment#onOptionsItemSelected

        (requireActivity() as AppCompatActivity).apply {
            // Redirect system "Back" press to our dispatcher
            onBackPressedDispatcher.addCallback(viewLifecycleOwner, backPressedDispatcher)

            // Set toolbar if it is in Fragment's layout. If you have a global toolbar that lives in Activity layout, then you don't need this line.
            setSupportActionBar(view.findViewById(R.id.toolbar))

            // Setup action bar to work with NavController
            setupActionBarWithNavController(findNavController())
        }
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        return if (item.itemId == android.R.id.home) {
            // Redirect "Up/Home" button clicks to our own function
            this@MyFragment.onBackPressed()
            true
        } else {
            super.onOptionsItemSelected(item)
        }
    }

    private fun onBackPressed() {
        // Work your magic! Show dialog etc.
    }

    override fun onDestroyView() {
        // It is optional to remove since our dispatcher is lifecycle-aware. But it wouldn't hurt to just remove it to be on the safe side.
        backPressedDispatcher.remove() 
        super.onDestroyView()
    }

 }

原回答 2019 年 1 月 3 日

晚会有点晚了，但是有了最新版本的导航组件 1.0.0-alpha09，现在我们有了 AppBarConfiguration.OnNavigateUpListener。

有关详细信息，请参阅以下链接： https://developer.android.com/reference/androidx/navigation/ui/AppBarConfiguration.OnNavigateUpListener https://developer.android.com/jetpack/docs/release-notes

Answer 5

旧更新

UPD：2019 年 4 月 3 日

现在简化了。更多信息 here

示例：

requireActivity().getOnBackPressedDispatcher().addCallback(getViewLifecycleOwner(), this);

@Override
public boolean handleOnBackPressed() {
    //Do your job here
    //use next line if you just need navigate up
    //NavHostFragment.findNavController(this).navigateUp(); 
    //Log.e(getClass().getSimpleName(), "handleOnBackPressed");
    return true;
    }

已弃用（自版本 1.0.0-alpha06 2019 年 4 月 3 日）：

自从 this, it can be implemented just using JetPack 在您的片段中实施 OnBackPressedCallback 并将其添加到 activity： getActivity().addOnBackPressedCallback(getViewLifecycleOwner(),this);

您的片段应如下所示：

public MyFragment extends Fragment implements OnBackPressedCallback {

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        
        getActivity().addOnBackPressedCallback(getViewLifecycleOwner(),this);
}
    
    @Override
    public boolean handleOnBackPressed() {
        //Do your job here
        //use next line if you just need navigate up
        //NavHostFragment.findNavController(this).navigateUp(); 
        //Log.e(getClass().getSimpleName(), "handleOnBackPressed");
        return true;
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        getActivity().removeOnBackPressedCallback(this);
    }
}

更新： 您的 activity 应该扩展 AppCompatActivity 或 FragmentActivity 并且在 Gradle 文件中：

 implementation 'androidx.appcompat:appcompat:{lastVersion}'

Answer 6

这是我的解决方案

对包含 NavHostFragment 片段的 activity 使用 androidx.appcompat.app.AppCompatActivity。

定义如下接口并在所有导航目标片段中实现

interface InterceptionInterface {

    fun onNavigationUp(): Boolean
    fun onBackPressed(): Boolean
}

在你的 activity 覆盖 onSupportNavigateUp 和 onBackPressed:

override fun onSupportNavigateUp(): Boolean {
        return getCurrentNavDest().onNavigationUp() || navigation_host_fragment.findNavController().navigateUp()
}

override fun onBackPressed() {
        if (!getCurrentNavDest().onBackPressed()){
            super.onBackPressed()
        }
}

private fun getCurrentNavDest(): InterceptionInterface {
        val currentFragment = navigation_host_fragment.childFragmentManager.primaryNavigationFragment as InterceptionInterface
        return currentFragment
}

此解决方案的优势在于，导航目标片段无需担心在分离后立即注销其侦听器。

Answer 7

我尝试了 Jurij Pitulja 解决方案，但我就是找不到 getOnBackPressedDispatcher 或 addOnBackPressedCallback 同样使用 Kiryl Tkach 的解决方案无法找到当前片段，所以这是我的：

interface OnBackPressedListener {
    fun onBackPressed(): Boolean
}

override fun onBackPressed() {
    val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment)
    val currentFragment = navHostFragment?.childFragmentManager!!.fragments[0]
    if (currentFragment !is OnBackPressedListener || !(currentFragment as OnBackPressedListener).onBackPressed()) super.onBackPressed()

这样你可以在片断中决定 activity 是否应该控制后退。

或者，您的所有活动都有 BaseActivity，您可以这样实现

override fun onBackPressed() {
    val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment)
    if (navHostFragment != null){
        val currentFragment = navHostFragment.childFragmentManager.fragments[0]
        if (currentFragment !is AuthContract.OnBackPressedListener ||
                !(currentFragment as AuthContract.OnBackPressedListener).onBackPressed()) super.onBackPressed()
    } else {
        super.onBackPressed()
    }
}

Answer 8

recommended 方法是将 OnBackPressedCallback 添加到 activity 的 OnBackPressedDispatcher。

requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner) { 
    // handle back event
}

Answer 9

在2.1.0-alpha06

如果你只想在当前片段中处理 backpress

requireActivity().onBackPressedDispatcher.addCallback(this@LoginFragment) {
    // handle back event
}

整个Activity

requireActivity().onBackPressedDispatcher.addCallback() {
    // handle back event
}

Answer 10

对于寻找 Kotlin 实现的任何人，请参见下文。

请注意，OnBackPressedCallback 似乎只能为内置 software/hardware 后退按钮提供自定义后退行为，而不是 button/home 作为向上按钮的后退箭头 button/home =29=]。为了同时覆盖 actionbar/toolbar 后退按钮的行为，我提供了适合我的解决方案。如果这是一个错误，或者您知道针对该情况的更好解决方案，请发表评论。

build.gradle

...
implementation "androidx.appcompat:appcompat:1.1.0-rc01"
implementation "androidx.navigation:navigation-fragment-ktx:2.0.0"
implementation "androidx.navigation:navigation-ui-ktx:2.0.0"
...

MainActivity.kt

...
import androidx.appcompat.app.AppCompatActivity
...

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        setContentView(R.layout.activity_main)

        ...

        val navController = findNavController(R.id.nav_host_fragment)
        val appBarConfiguration = AppBarConfiguration(navController.graph)

        // This line is only necessary if using the default action bar.
        setupActionBarWithNavController(navController, appBarConfiguration)

        // This remaining block is only necessary if using a Toolbar from your layout.
        val toolbar = findViewById<Toolbar>(R.id.toolbar)
        toolbar.setupWithNavController(navController, appBarConfiguration)
        // This will handle back actions initiated by the the back arrow 
        // at the start of the toolbar.
        toolbar.setNavigationOnClickListener {
            // Handle the back button event and return to override 
            // the default behavior the same way as the OnBackPressedCallback.
            // TODO(reason: handle custom back behavior here if desired.)

            // If no custom behavior was handled perform the default action.
            navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
        }
    }

    /**
     * If using the default action bar this must be overridden.
     * This will handle back actions initiated by the the back arrow 
     * at the start of the action bar.
     */
    override fun onSupportNavigateUp(): Boolean {
        // Handle the back button event and return true to override 
        // the default behavior the same way as the OnBackPressedCallback.
        // TODO(reason: handle custom back behavior here if desired.)

        // If no custom behavior was handled perform the default action.
        val navController = findNavController(R.id.nav_host_fragment)
        return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
    }
}

MyFragment.kt

...
import androidx.activity.OnBackPressedCallback
import androidx.fragment.app.Fragment
...

class MyFragment : Fragment() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val onBackPressedCallback = object : OnBackPressedCallback(true) {
            override fun handleOnBackPressed() {
                // Handle the back button event
            }
        }
        requireActivity().getOnBackPressedDispatcher().addCallback(this, onBackPressedCallback)
    }
}

官方文档可以在https://developer.android.com/guide/navigation/navigation-custom-back

查看

Answer 11

如果您的应用程序使用 BaseFragment，则可以将 onBackPressedDispatcher 添加到您的基本片段。

//Make a BaseFragment for all your fragments
abstract class BaseFragment : Fragment() {

private lateinit var callback: OnBackPressedCallback

/**
 * SetBackButtonDispatcher in OnCreate
 */

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setBackButtonDispatcher()
}

/**
 * Adding BackButtonDispatcher callback to activity
 */
private fun setBackButtonDispatcher() {
    callback = object : OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            onBackPressed()
        }
    }
    requireActivity().onBackPressedDispatcher.addCallback(this, callback)
}

/**
 * Override this method into your fragment to handleBackButton
 */
  open fun onBackPressed() {
  }

}

通过扩展 basefragment

覆盖片段中的 onBackPressed()

//How to use this into your fragment
class MyFragment() : BaseFragment(){

private lateinit var mView: View

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    mView = inflater.inflate(R.layout.fragment_my, container, false)
    return mView.rootView
}

override fun onBackPressed() {
    //Write your code here on back pressed.
}

}

Answer 12

我在main里写的activity是这样的，

override fun onSupportNavigateUp(): Boolean {
        return findNavController(R.id.my_nav_host_fragment).navigateUp(appBarConfiguration)
    }

Answer 13

根据您的逻辑，如果您只想关闭当前片段，则必须传递viewLifecycleOwner，代码如下所示：

   requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, object : OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            requireActivity().finish()
        }
    })

但是，如果您想在 backPressed 上关闭应用程序，无论从哪个片段（可能您不希望这样！），请不要传递 viewLifecycleOwner。此外，如果您想禁用后退按钮，请不要在 handleOnBackPressed() 中执行任何操作，请参见下文：

 requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, object : OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            // do nothing it will disable the back button
        }
    })

Answer 14

这是 2 行代码，可以从片段中监听返回压力，[已测试并正在运行]

  requireActivity().getOnBackPressedDispatcher().addCallback(getViewLifecycleOwner(), new OnBackPressedCallback(true) {
        @Override
        public void handleOnBackPressed() {

            //setEnabled(false); // call this to disable listener
            //remove(); // call to remove listener
            //Toast.makeText(getContext(), "Listing for back press from this fragment", Toast.LENGTH_SHORT).show();
     }

Answer 15

推荐的方法对我有用，但在更新我的库后 implementation 'androidx.appcompat:appcompat:1.1.0'

执行如下

 val onBackPressedCallback = object : OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            // Handle the back button event
        }
    }
    requireActivity().onBackPressedDispatcher.addCallback(this, onBackPressedCallback)

使用 Kotlin

Answer 16

如果您使用导航组件，请在您的 onCreateView() 方法中遵循以下代码（在此示例中，我只想通过此片段关闭我的应用程序）

 OnBackPressedCallback backPressedCallback = new OnBackPressedCallback(true) {
        @Override
        public void handleOnBackPressed() {
            new AlertDialog.Builder(Objects.requireNonNull(getActivity()))
                    .setIcon(R.drawable.icon_01)
                    .setTitle(getResources().getString(R.string.close_app_title))
                    .setMessage(getResources().getString(R.string.close_app_message))
                    .setPositiveButton(R.string.yes, new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            getActivity().finish();
                        }
                    })
                    .setNegativeButton(R.string.no, null)
                    .show();
        }
    };
    requireActivity().getOnBackPressedDispatcher().addCallback(this, backPressedCallback);

Answer 17

您可以使用 OnBackPressedDispatcher 提供自定义后退导航

class MyFragment : Fragment() {

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    // This callback will only be called when MyFragment is at least Started.
    val callback = requireActivity().onBackPressedDispatcher.addCallback(this) {
        // Handle the back button event
// and if you want to need navigate up
//NavHostFragment.findNavController(this).navigateUp()
    }

    // The callback can be enabled or disabled here or in the lambda
}
}

更多解释见android官方指南：https://developer.android.com/guide/navigation/navigation-custom-back

Answer 18

如果您希望工具栏后退按钮也有相同的行为，只需将其添加到 activity:

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (item.getItemId() == android.R.id.home) {
        getOnBackPressedDispatcher().onBackPressed();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

Answer 19

我的意见 requireActivity().onBackPressed()

requireActivity().onBackPressed()

Answer 20

只需添加这些行

     override fun onBackPressed() {
            if(navController.popBackStack().not()) {
            //Last fragment: Do your operation here 
            finish()
   }

navController.popBackStack() 如果这不是您的最后一个片段，则只会弹出您的片段

Answer 21

如果您使用片段或将其添加到您的按钮点击侦听器中，请使用此选项。这对我有用。

requireActivity().onBackPressed()

当 activity 检测到用户按下后退键时调用。在调用 android.app.Activity#onBackPressed()} 的默认行为之前，getOnBackPressedDispatcher() OnBackPressedDispatcher} 将有机会处理后退按钮。

Answer 22

我搜索了很多话题，其中 none 个有效。终于找到一个：

MainActivity.java

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Toolbar mToolbar = findViewById(R.id.topAppBar);
    setSupportActionBar(mToolbar);
}

@Override
public boolean onSupportNavigateUp() {
    navController.navigateUp();
    return super.onSupportNavigateUp();
}

MyFragment.java

@Override
public void onViewCreated(@NonNull final View view, @Nullable Bundle savedInstanceState) {
    Toolbar mToolbar = (MainActivity) getActivity().findViewById(R.id.topAppBar);
    mToolbar.setNavigationOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // Do something when uses presses back button (showing modals, messages,...)
            // Note that this will override behaviour of back button
        }
    });
}

@Override
public void onStop() {
    // Reset back button to default behaviour when we leave this fragment
    Toolbar mToolbar = (MainActivity) getActivity().findViewById(R.id.topAppBar);
    mToolbar.setNavigationOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mainActivity.onBackPressed();
        }
    });

    super.onStop();
}

Answer 23

只需为片段创建一个扩展函数

fun Fragment.onBackPressedAction(action: () -> Boolean) {
    requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, object :
        OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            this.isEnabled = action()
            if (!this.isEnabled) {
                requireActivity().onBackPressed()
            }
        }
    })
}

然后在片段中将代码放入 onCreateView（操作必须 return false 才能调用 activity onBackPressed）

onBackPressedAction { //do something }

Answer 24

我需要同时支持真正的后退按钮和工具栏后退按钮，并且能够在这两种情况下覆盖“后退”单击（以显示对话框或其他内容）。我在 activity 中创建了一个附加方法，并在 fragments:

中创建了相应的布尔检查（在我的例子中为 'onBackPressed'）

// Process hardware Back button
override fun onBackPressed() {
    if (canCloseActivity()) {
        super.onBackPressed()
    }
}

// Process toobar Back and Menu button
override fun onSupportNavigateUp(): Boolean {
    if (canCloseActivity()) {
        return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
    }
    return false
}

// Do real check if has unfinished tasks, return false to override activity closing
private fun canCloseActivity(): Boolean {
    val currentFragment = navHostFragment.childFragmentManager.primaryNavigationFragment

    return when {
        currentFragment is MyFragment && currentFragment.onBackPressed() -> false

        drawerLayout.isOpen -> {
            drawerLayout.close()
            false
        }
        fullScreenPreviewLayout.visibility == View.VISIBLE -> {
            closeFullscreenPreview()
            false
        }
        else -> true
    }
}

Answer 25

简单地说，在 Fragment 的 onCreate() 方法中，在 super.onCreate(savedInstanceState) 之后使用此代码：

// This callback will only be called when MyFragment is at least Started.
val callback = requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner) {
            // Handle the back button event
}

Answer 26

如果您实际上正在尝试专门处理后退按钮，那么您可以使用@Jurij Pitulja 的回答。

但是，如果您想要弹出 SecondFragment（开始片段 FirstFragment）而不是 return 到 FirstFragment，然后你可以使用：

Navigation.findNavController(view).popBackStack()

来自 SecondFragment。这样，当您从 FirstFragment.

Answer 27

使用导航组件这对我有好处：

Navigation.findNavController(requireView()).popBackStack()

android documentation

Answer 28

ktx 版本：

fun Fragment.handleBackButtonEvent(
    onBackPressed: OnBackPressedCallback.() -> Unit
) {
    requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner) {
        onBackPressed()
    }
}

您可以简单地在 Fragmnet 中使用它。

Answer 29

FragmentExtenstions.kt

fun Fragment.onBackPressedCustomAction(action: () -> Unit) {
  requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, object : OnBackPressedCallback(true) {
    override
    fun handleOnBackPressed() {
      action()
    }
  })
}

YourPrettyFragment.kt

onBackPressedCustomAction {
  // Your custom action here
}

Answer 30

Kotlin 答案

使用popBackStack()示例：

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

    mButton.setOnClickListener {
        Navigation.findNavController(view).popBackStack() // You need this line.
    }
}

处理 Android 导航组件中的后退按钮

Handling back button in Android Navigation Component

navigation

android

fragment

android-jetpack

最新更新 - 2019 年 4 月 25 日

旧更新