片段工具栏中的后退按钮

Question

我有一个选项卡式布局下的片段活动。这是我的应用程序层次结构=> MainActivity.class> FragmentExplore.class> FragmentOne.class或FragmentTwo.class或FragmentTheree.class。

我想在主要活动的工具栏中设置后退按钮。我试图在这些活动和片段的所有xml和java文件中插入工具栏的java和xml代码。但是，后退按钮不起作用。

这是该工具栏的后退按钮的Java和xml代码：

 <com.google.android.material.appbar.AppBarLayout
        ...>
        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/colorPrimary"
            />
</com.google.android.material.appbar.AppBarLayout>

        Toolbar toolbar = view.findViewById(R.id.toolbar);
        toolbar.setNavigationIcon(R.drawable.ic_rating);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
        Toast.makeText(getActivity(), "back pressed", Toast.LENGTH_SHORT).show();
            }
        });

类似地，这是MainActivity.class：

public class MainActivity extends AppCompatActivity {
    private final static String COLLAPSING_TOOLBAR_FRAGMENT_TAG = "collapsing_toolbar";
    private final static String SELECTED_TAG = "selected_index";
    private final static int COLLAPSING_TOOLBAR = 0;

    private static int selectedIndex;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        selectedIndex = COLLAPSING_TOOLBAR;
        getSupportFragmentManager().beginTransaction().add(R.id.fragment_container,
                new FragmentExplore(), COLLAPSING_TOOLBAR_FRAGMENT_TAG).commit();
    }
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt(SELECTED_TAG, selectedIndex);
    }
    }
}

FragmentExplore：

public class FragmentExplore extends Fragment {
    public FragmentExplore() {
    }
    @Override
    public void onAttach(Context activity) {
        super.onAttach(activity);
        mainActivity = (MainActivity) activity;
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.tab_layout, container, false);

        AppBarLayout appBarLayout = view.findViewById(R.id.tab_appbar_layout);
        ((CoordinatorLayout.LayoutParams) appBarLayout.getLayoutParams()).setBehavior(new AppBarLayoutBehavior());

        tabLayout = view.findViewById(R.id.tabs);
        tabLayout.setTabMode(TabLayout.MODE_SCROLLABLE);
        tabLayout.setTabGravity(TabLayout.GRAVITY_CENTER);

        viewPager = view.findViewById(R.id.viewpager);
        viewPager.setOffscreenPageLimit(tab_count);

        toolbar = view.findViewById(R.id.toolbar);
        setupToolbar();

        viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));

        tabLayout.post(new Runnable() {
            @Override
            public void run() {
                tabLayout.setupWithViewPager(viewPager);
                viewPager.setCurrentItem(1);
            }
        });
        return view;
    }

    public class MyAdapter extends FragmentPagerAdapter {
        private MyAdapter(FragmentManager fm) {
            super(fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
        }
        @Override
        public Fragment getItem(int position) {...}

        @Override
        public int getCount() {
            return tab_count;
        }

        @Override
        public CharSequence getPageTitle(int position) {...}
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
    }

    private void setupToolbar() {
        toolbar.setTitle(getString(R.string.app_name));
        mainActivity.setSupportActionBar(toolbar);
    }

}

和FragmentOne.class：

public class FragmentOne extends Fragment {

    View view;

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.activity_frag_one, container, false);
        return view;
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        inflater.inflate(R.menu.menuo, menu);
        super.onCreateOptionsMenu(menu, inflater);
    }

    }
}

我试图将那些工具栏的xml和java代码放在不同的位置，但无法解决此问题。提前非常感谢。

Answer 1

您应在致电setSupportActionBar之后进行设置，然后尝试此操作

    private void setupToolbar() {
        toolbar.setTitle(getString(R.string.app_name));
        mainActivity.setSupportActionBar(toolbar);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
        Toast.makeText(getActivity(), "back pressed", Toast.LENGTH_SHORT).show();
            }
        });
    }