如何仅在第一个片段上隐藏浮动操作按钮？

Question

请告诉我如何仅在 Android Studio 的第一个片段上隐藏浮动操作按钮？ 我使用导航抽屉，这是 MainActivity.java 中的代码，我在其中调用片段：

    public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    FirstFragment fragment1;
    SecondFragment fragment2;
    ThirdFragment fragment3;
    


    @SuppressLint("StaticFieldLeak")
    public static Context currentContext;

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

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

        FloatingActionButton fab = findViewById(R.id.fab);

        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });



        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

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

        fragment1 = new FirstFragment();
        fragment2 = new SecondFragment();
        fragment3 = new ThirdFragment();
        
        getSupportFragmentManager().beginTransaction().add(R.id.nav_host_fragment, fragment1).commit();
        if (savedInstanceState==null){
           }

       
    }


    @Override
    public void onBackPressed() {
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
       
        int id = item.getItemId();
        return super.onOptionsItemSelected(item);
    }





@Override
    public boolean onNavigationItemSelected(MenuItem item) {
        int id = item.getItemId();
        FragmentTransaction ftrans = getSupportFragmentManager().beginTransaction();
        String title = "App Name";

        switch (id) {
            case (R.id.nav_fr2):
                ftrans.replace(R.id.nav_host_fragment, fragment2);
                title="Fragment 2";
                break;

            case (R.id.nav_fr3):
                ftrans.replace(R.id.nav_host_fragment, fragment3);
                title="Fragment 3";
                break;

           
            default:
                ftrans.replace(R.id.nav_host_fragment, fragment1);
                break;
        }
        getSupportActionBar().setTitle(title);
        ftrans.commit();
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

这是我的主要活动的代码。 当我添加 fab.setVisibility(View.GONE); Android Studio 显示错误“无法解析符号工厂”。 当我在这个块中添加 FloatingActionButton fab = findViewById(R.id.fab); 晶圆厂未显示在所有片段中。

Answer 1

您可以使您的fab成为 class 级别变量而不是本地变量，然后根据您的需要更改可见性，示例如下：

    FirstFragment fragment1;
    SecondFragment fragment2;
    ThirdFragment fragment3;



    @SuppressLint("StaticFieldLeak")
    public static Context currentContext;

    // declare it here
    FloatingActionButton fab;


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

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        //assign here like this
        fab = findViewById(R.id.fab);

        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });



        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

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

        fragment1 = new FirstFragment();
        fragment2 = new SecondFragment();
        fragment3 = new ThirdFragment();

        getSupportFragmentManager().beginTransaction().add(R.id.nav_host_fragment, fragment1).commit();
        if (savedInstanceState==null){
        }


    }


    @Override
    public void onBackPressed() {
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        int id = item.getItemId();
        return super.onOptionsItemSelected(item);
    }





    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        int id = item.getItemId();
        FragmentTransaction ftrans = getSupportFragmentManager().beginTransaction();
        String title = "App Name";

        switch (id) {
            case (R.id.nav_fr2):
                // set this visible when fragment 2 selected
                fab.setVisibility(View.VISIBLE);
                ftrans.replace(R.id.nav_host_fragment, fragment2);
                title="Fragment 2";
                break;

            case (R.id.nav_fr3):
                // set this visible when fragment 3 selected
                fab.setVisibility(View.VISIBLE);
                ftrans.replace(R.id.nav_host_fragment, fragment3);
                title="Fragment 3";
                break;


            default:
                // hide when fragment 1 selected
                fab.setVisibility(View.GONE);
                ftrans.replace(R.id.nav_host_fragment, fragment1);
                break;
        }
        getSupportActionBar().setTitle(title);
        ftrans.commit();
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }