Question

感谢您花时间在我的身上。在我的应用程序中，我使用android studio导航抽屉模板。但问题是，当我旋转手机时，先前片段的布局显示在当前片段上方。

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，活动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onCreate()的新调用中添加了另一个片段，这就是为什么你有两个片段。要解决此问题，您应首先检查savedInstanceState中的onCreate()参数是否为空，即它是第一次创建活动，而不仅仅是因为轮换更改而重新启动，还是决定是否添加片段而不是每当活动调用onCreate()

时添加

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导航抽屉模板在旋转时当前片段更改上方查看其他片段

1 个答案: