如何通过背压完美地处理底部导航

Question

我正在使用底部导航栏,但我没有得到完美的底部导航栏.

我的MainActivity班级:

public class MainActivity extends AppCompatActivity {

    private static final String SELECTED_ITEM = "selected_item";

    private BottomNavigationView bottomNavigationView;
    private Toolbar toolbar;
    private MenuItem menuItemSelected;
    private int mMenuItemSelected;


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

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        bottomNavigationView = (BottomNavigationView) findViewById(R.id.bottom_navigation);
        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                selectFragment(item);
                return true;
            }
        });

        //Always load first fragment as default
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.frameLayout, new AnnouncementFragment());
        fragmentTransaction.commit();

        if (savedInstanceState != null) {
            mMenuItemSelected = savedInstanceState.getInt(SELECTED_ITEM, 0);
            menuItemSelected = bottomNavigationView.getMenu().findItem(mMenuItemSelected);
        } else {
            menuItemSelected = bottomNavigationView.getMenu().getItem(0);
        }

        selectFragment(menuItemSelected);
    }

    private void selectFragment(MenuItem item) {
        Fragment fragment = null;
        Class fragmentClass;
        switch (item.getItemId()) {
            case R.id.action_announcement:
                fragmentClass = AnnouncementFragment.class;
                break;
            case R.id.action_menu:
                fragmentClass = MenuFragment.class;
                break;
            case R.id.action_menu_reports:
                fragmentClass = ReportFragment.class;
                break;
            case R.id.action_setting:
                fragmentClass = SettingFragment.class;
                break;

            default:
                fragmentClass = AnnouncementFragment.class;
        }

        try {
            fragment = (Fragment) fragmentClass.newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.frameLayout, fragment).commit();
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putInt(SELECTED_ITEM, mMenuItemSelected);
        super.onSaveInstanceState(outState);
    }

我的背部压力也不正常:

 @Override
    public void onBackPressed() {
        MenuItem homeItem = bottomNavigationView.getMenu().getItem(0);
        if (mMenuItemSelected != homeItem.getItemId()) {
            selectFragment(homeItem);
        } else {
            super.onBackPressed();
        }
    }

我应该怎么做,因为底部菜单栏上的分布不均匀.如何正确维护菜单空间而不分布不均匀.

在这里,我附上了我在AVD上获得的结果

Answer 1

根据材料设计指南

在Android上,"后退"按钮不会在底部导航栏视图之间导航.

编辑:材料设计链接不再提及后退按钮行为.

按后退按钮可以退出应用程序,这是默认行为,例如在Google Photo中...

FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.content, fragment);
// note: there is NOT a addToBackStack call
fragmentTransaction.commit();

......或者将用户带到家庭区域,如果再次按下,则在出口处.

就个人而言,我发现这最后的模式要好得多.

要在没有覆盖的情况下获取它,onBackPressed您需要识别主片段并将其与所有其他片段区分开来

navigation = (BottomNavigationView) findViewById(R.id.navigation);
navigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_home:
                viewFragment(new HomeFragment(), FRAGMENT_HOME);
                return true;
            case R.id.navigation_page_1:
                viewFragment(new OneFragment(), FRAGMENT_OTHER);
                return true;
            case R.id.navigation_page_2:
                viewFragment(new TwoFragment(), FRAGMENT_OTHER);
                return true;
        }
        return false;
    }
});

你现在要做的是写下必须的viewfragment方法:

1. 知道有多少片段中有叠前的commit

2. 如果片段不是 "home type",请将其保存到堆栈之前commit

3. OnBackStackChangedListener当堆栈减少时(即当我按下时)添加一个,删除所有 不是 "home type"(POP_BACK_STACK_INCLUSIVE)的片段,将我们带到home片段

下面带有注释的完整方法

private void viewFragment(Fragment fragment, String name){
    final FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.content, fragment);
    // 1. Know how many fragments there are in the stack
    final int count = fragmentManager.getBackStackEntryCount();
    // 2. If the fragment is **not** "home type", save it to the stack
    if( name.equals( FRAGMENT_OTHER) ) {
        fragmentTransaction.addToBackStack(name);
    }
    // Commit !
    fragmentTransaction.commit();
    // 3. After the commit, if the fragment is not an "home type" the back stack is changed, triggering the
    // OnBackStackChanged callback
    fragmentManager.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
        @Override
        public void onBackStackChanged() {
            // If the stack decreases it means I clicked the back button
            if( fragmentManager.getBackStackEntryCount() <= count){
                // pop all the fragment and remove the listener
                fragmentManager.popBackStack(FRAGMENT_OTHER, POP_BACK_STACK_INCLUSIVE);
                fragmentManager.removeOnBackStackChangedListener(this);
                // set the home button selected
                navigation.getMenu().getItem(0).setChecked(true);
            }
        }
    });
}

Answer 2

试试这个

@Override
    public void onBackPressed() {
        BottomNavigationView bottomNavigationView = (BottomNavigationView) findViewById(R.id.navigation);
        int seletedItemId = bottomNavigationView.getSelectedItemId();
        if (R.id.home != seletedItemId) {
            setHomeItem(MainActivity.this);
        } else {
            super.onBackPressed();
        }
    }

public static void setHomeItem(Activity activity) {
    BottomNavigationView bottomNavigationView = (BottomNavigationView)
            activity.findViewById(R.id.navigation);
    bottomNavigationView.setSelectedItemId(R.id.home);
}

Answer 3

@Override
    public void onBackPressed() {
        BottomNavigationView mBottomNavigationView = findViewById(R.id.navigation);
        if (mBottomNavigationView.getSelectedItemId() == R.id.navigation_home)
        {
            super.onBackPressed();
            finish();
        }
        else
        {
            mBottomNavigationView.setSelectedItemId(R.id.navigation_home);
        }
    }

Answer 4

这也许有点晚了，但是我认为做到这一点的最好方法就是这么简单。

 @Override
public void onBackPressed() {
    if (mBottomNavigationView.getSelectedItemId() == R.id.action_home) {
        super.onBackPressed();
    } else {
        mBottomNavigationView.setSelectedItemId(R.id.action_home);
    }
}

希望对您有所帮助，并祝您编程愉快：)

Answer 5

onBackPressed不适用于我。所以我用了

 @Override
 protected void onResume() {
    super.onResume();
    bottomNavigationView.getMenu().getItem(0).setChecked(true);
 }