如何正确实现导航抽屉中顶部的后退按钮？

How to properly implement the top back button in navigation drawer?(如何正确实现导航抽屉中顶部的后退按钮？)

问题描述

我目前正试图在我的天气应用程序中添加导航抽屉，所以我看了一个YouTube 教程，并且能够以我想要的方式实现它，直到我意识到 我看的教程没有介绍如何实现向上/顶部后退 按钮，所以事实上，我现在不能回到 打开任何导航选项卡后的默认片段。我搜索了几个 网站和YouTube视频寻找如何实现顶部Back的教程 按钮，但没看到/找不到。我也搜索了这个网站，仍然 在这里没有发现有类似问题的人。请问有谁能帮忙吗？ 以下是我的应用程序当前状态的屏幕截图：https://i.stack.imgur.com/SeSjV.png但如果我打开任何导航栏选项(即设置)并单击"上一步"，我将无法返回到显示天气的默认片段。它也没有"上-后"按钮。

当前，单击"上一步"仅退出应用程序。

这是我尝试过的唯一代码，但不起作用：

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    if (item.getItemId() == android.R.id.home) {
        int backStackCount = fragmentManager.getBackStackEntryCount();//check currently how many frags loaded
        if (backStackCount > 0) {
            fragmentManager.popBackStack(); //go back to previously loaded fragment
        }   
    }

    return super.onOptionsItemSelected(item);
}

它出现以下错误：

错误：找不到符号 int backStackCount=fragmentManager.getBackStackEntryCount()；//check当前有多少 加载的碎片

这是我的活动代码：

public class HomeActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
    private DrawerLayout drawer;
    // Last update time, click sound, search button, search panel.
    TextView timeField;
    MediaPlayer player;
    ImageView Search;
    EditText textfield;
    // For scheduling background image change(using constraint layout, start counting from dubai, down to statue of liberty.
    ConstraintLayout constraintLayout;
    public static int count = 0;
    int[] drawable = new int[]{R.drawable.dubai, R.drawable.norway, R.drawable.eiffel_tower, R.drawable.hong_kong, R.drawable.statue_of_liberty,
            R.drawable.beijing, R.drawable.chicago, R.drawable.colombia, R.drawable.vienna,R.drawable.tokyo};
    Timer _t;

    private WeatherDataViewModel viewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        // use home activity layout.

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        // Allow activity to make use of the toolbar

        drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        viewModel = new ViewModelProvider(this).get(WeatherDataViewModel.class);

        // Trigger action to open & close nevigation drawer
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar
                , R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        timeField = findViewById(R.id.textView9);
        Search = findViewById(R.id.imageView4);
        textfield = findViewById(R.id.textfield);
        //  find the id's of specific variables.

        BottomNavigationView bottomNavigationView = findViewById(R.id.bottomNavigationView);
        // host 3 fragments along with bottom navigation.
        final NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment);
        assert navHostFragment != null;
        final NavController navController = navHostFragment.getNavController();
        NavigationUI.setupWithNavController(bottomNavigationView, navController);

        // Make hourly & daily tab unusable
        bottomNavigationView.setOnNavigationItemSelectedListener(item -> {

            if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
                getSupportFragmentManager().popBackStack();
            }
            return false;
        });

        navController.addOnDestinationChangedListener((controller, destination, arguments) -> navController.popBackStack(destination.getId(), false));

        // For scheduling background image change
        constraintLayout = findViewById(R.id.layout);
        constraintLayout.setBackgroundResource(R.drawable.dubai);
        _t = new Timer();
        _t.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                // run on ui thread
                runOnUiThread(() -> {
                    if (count < drawable.length) {

                        constraintLayout.setBackgroundResource(drawable[count]);
                        count = (count + 1) % drawable.length;
                    }
                });
            }
        }, 5000, 5000);

        Search.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // make click sound when search button is clicked.
                player = MediaPlayer.create(HomeActivity.this, R.raw.click);
                player.start();

                getWeatherData(textfield.getText().toString().trim());
                // make use of some fragment's data

                Fragment currentFragment = navHostFragment.getChildFragmentManager().getFragments().get(0);
                if (currentFragment instanceof FirstFragment) {
                    FirstFragment firstFragment = (FirstFragment) currentFragment;
                    firstFragment.getWeatherData(textfield.getText().toString().trim());
                } else if (currentFragment instanceof SecondFragment) {
                    SecondFragment secondFragment = (SecondFragment) currentFragment;
                    secondFragment.getWeatherData(textfield.getText().toString().trim());
                } else if (currentFragment instanceof ThirdFragment) {
                    ThirdFragment thirdFragment = (ThirdFragment) currentFragment;
                    thirdFragment.getWeatherData(textfield.getText().toString().trim());
                }
            }

            private void getWeatherData(String name) {

                ApiInterface apiInterface = ApiClient.getClient().create(ApiInterface.class);

                Call<Example> call = apiInterface.getWeatherData(name);

                call.enqueue(new Callback<Example>() {
                    @Override
                    public void onResponse(@NonNull Call<Example> call, @NonNull Response<Example> response) {

                        try {
                            assert response.body() != null;
                            timeField.setVisibility(View.VISIBLE);
                            timeField.setText("First Updated:" + " " + response.body().getDt());
                        } catch (Exception e) {
                            timeField.setVisibility(View.GONE);
                            timeField.setText("First Updated: Unknown");
                            Log.e("TAG", "No City found");
                            Toast.makeText(HomeActivity.this, "No City found", Toast.LENGTH_SHORT).show();
                        }
                    }

                    @Override
                    public void onFailure(@NotNull Call<Example> call, @NotNull Throwable t) {
                        t.printStackTrace();
                    }

                });
            }

        });
    }

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.settings_id:
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment,
                        new Settings()).commit();
                break;
            case R.id.ads_upgrade_id:
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment,
                        new Upgrade()).commit();
                break;
            case R.id.privacy_policy_id:
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment,
                        new Privacy_Policy()).commit();
                break;
        }
        drawer.closeDrawer(GravityCompat.START);

        return true;
    }

    @Override
    public void onBackPressed() {
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
            // Open/close drawer animation
        }
    }

推荐答案

if (item.getItemId() == android.R.id.home) {
    int backStackCount = fragmentManager.getBackStackEntryCount();//check currently how many frags loaded
    if (backStackCount > 0) {
        fragmentManager.popBackStack(); //go back to previously loaded fragment
    }   
}

当前，单击"上一步"仅退出应用程序。

使用popBackStack()将弹出使您的应用程序存在的后栈，但您只需返回到默认片段。

要解决此问题，您需要更改抽屉汉堡按钮的行为，以便有时可以使用它打开抽屉的navView布局，有时可以使用它返回到默认片段；后者是在您要添加顶部的后退按钮时使用的。

如何实现导航抽屉的上/上后退按钮

这需要访问使您能够将侦听器添加到汉堡点击的setToolbarNavigationClickListener方法。

在这种情况下，您需要在onCreate()方法Add：

中根据需要返回到Home片段

toggle.setToolbarNavigationClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        // Enable the functionality of opening the side drawer, when the burger icon is clicked
        toggle.setDrawerIndicatorEnabled(true); // Show the burger icon & enable the drawer funcionality
        navController.navigate(R.id.home); // Back to default fragment (replace home with your default fragment id in the navGraph)
    }
});

剩下的部分是在您想要转到某个片段时显示后退按钮

并使用toggle.setDrawerIndicatorEnabled()启用/禁用单击主页/汉堡图标时打开/关闭抽屉的功能

navController.addOnDestinationChangedListener(new NavController.OnDestinationChangedListener() {
    @Override
    public void onDestinationChanged(@NonNull NavController controller, @NonNull NavDestination destination, @Nullable Bundle arguments) {

        // Repeat this condition for all the Fragments that you want to show the back button
        if (destination.getId() == R.id.settings_id) { // replace `settings_id` with your fragment id in the navGraph that you want to show the back button
            // Disable the functionality of opening the side drawer, when the burger icon is clicked & show the UP button instead
            toggle.setDrawerIndicatorEnabled(false);

        } 

    }
});

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