使用 android studio 导航抽屉模板在当前片段变化上方查看其他片段

Question

感谢您花时间解答我的问题。在我的应用程序中，我使用 android 工作室导航抽屉模板。但问题是，当我旋转 phone 时，前一个片段的布局显示在当前片段的上方。

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        Fragment fragment = null;
        Class fragmentClass = null;


       /* if (savedInstanceState == null){
            try{
                fragment = (Fragment) fragmentClass.newInstance();
            }catch (Exception e){
                e.printStackTrace();
            }
        }*/
        fragment = new Login();
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.add(R.id.fragment, fragment);
        fragmentTransaction.commit();




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

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

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {

        // Handle navigation view item clicks here.
        int id = item.getItemId();
        Fragment fragment =null ;
        Class fragmentClas = null;

        if (id == R.id.nav_camera) {
            // Handle the camera action
            fragment = new Attendance();
            FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment, fragment);
            fragmentTransaction.commit();
        } else if (id == R.id.nav_gallery) {

            fragment = new AddStudent();
            FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment, fragment);
            fragmentTransaction.commit();
        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_manage) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

       /* FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();*/

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

}

Answer 1

当您旋转设备时，activity 会保存其当前状态并保留当前片段，然后将其销毁并重新创建，即再次调用 onCreate()。在它被销毁之前你有一个片段，现在它在对 onCreate() 的新调用中添加了另一个片段，这就是你有 2 个片段的原因。要解决此问题，您应该首先检查 onCreate() 中的 savedInstanceState 参数是否为空，即它是 activity 的第一次创建，而不仅仅是由于旋转变化或其他原因而重新启动，然后决定添加每当 activity 调用 onCreate()

时，是否片段而不是添加到

if(savedInstanceState == null) {
    // Add the fragment because it's normal creation
    fragment = new Login();
    FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.add(R.id.fragment, fragment);
    fragmentTransaction.commit();
}

使用 android studio 导航抽屉模板在当前片段变化上方查看其他片段

Other Fragment is viewed above the current fragment changes on rotation with android studio navigation drawer template

android

navigation-drawer

android-studio-2.0