片段扩展 ListFragment 无法在 MainActivity 中打开

Question

请告诉我如何打开 A Fragment extends ListFragment from MainActivity.java？

这是我的代码：

主活动：

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

   ImageView imageView1;

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

    ParseUser currentUser = ParseUser.getCurrentUser();
    //String currentUserId = currentUser.getObjectId().toString().trim();

    if (currentUser != null) {
        // do stuff with the user


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

    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);

       // final View headerLayout = navigationView.inflateHeaderView(R.layout.nav_header_main);
        final View header = navigationView.getHeaderView(0);
        TextView text = (TextView) header.findViewById(R.id.TxtUsernametitle);
        TextView Tmail = (TextView)header.findViewById(R.id.textmail);
        imageView1 = (ImageView)header.findViewById(R.id.profile_image2);


        String Tusern = currentUser.getUsername();
        String Tmails = currentUser.getEmail();
        text.setText(Tusern);
        Tmail.setText(Tmails);
        ParseQuery<ParseObject> query = ParseQuery.getQuery("Profile");
        String UsiD = currentUser.getObjectId();
        query.whereEqualTo("userID",UsiD);
        query.getFirstInBackground(new GetCallback<ParseObject>() {
            public void done(ParseObject object, ParseException e) {
                if (e == null) {
                    ParseFile fileObject = (ParseFile) object.get("picture");
                    if (object.get("picture") != null) {
                        String imgpath = fileObject.getUrl();
                        Toast.makeText(MainActivity.this, imgpath, Toast.LENGTH_LONG).show();

                        Glide.with(MainActivity.this).load(imgpath).into(imageView1);
                    } else {
                        imageView1.setImageResource(R.drawable.image);
                    }
                } else {
                    Toast.makeText(MainActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();
                }
            }
        });



   FragmentManager fm = getFragmentManager();
   fm.beginTransaction().replace(R.id.content_frame,new MainFragments()).commit();



    } else {
        // show the signup or login screen
        Intent takeUsertoLogin = new Intent(MainActivity.this, LoginActivity.class);
       startActivity(takeUsertoLogin);
    }
}

@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.
    FragmentManager fm2 =getFragmentManager();

    int id = item.getItemId();
switch (id){
    case R.id.Ads_page:
        fm2.beginTransaction().replace(R.id.content_frame,new UpdateFragment()).commit();
        break;

}
        return super.onOptionsItemSelected(item);
    }

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

    FragmentManager fm =getFragmentManager();

    int id = item.getItemId();

    if (id == R.id.nav_camara) {
        fm.beginTransaction().replace(R.id.content_frame,new ImportFragments()).commit();

    } else if (id == R.id.nav_gallery) {
        fm.beginTransaction().replace(R.id.content_frame,new MainFragments()).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) {

    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}
@Override
public void onDestroy() {
    super.onDestroy();
    ParseUser.logOut();
}
}

主要片段：

    public class MainFragments extends ListFragment {
    protected List<ParseObject> Ads;
Button btn_LogOut;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_main,container, false);

    ParseQuery<ParseObject> query = new ParseQuery<ParseObject>("Ads");
    query.findInBackground(new FindCallback<ParseObject>() {


        @Override
public void done(List<ParseObject> Adsobjects, ParseException e) {
    if(e==null){
        Ads=Adsobjects;
        AdsAdapter adapter =new AdsAdapter(getListView().getContext(),Ads);
        setListAdapter(adapter);
    }else{

    }

}
});



    btn_LogOut=(Button)rootView.findViewById(R.id.buttonlogout);

    btn_LogOut.setOnClickListener(new View.OnClickListener() {

           public void onClick(View v) {
            ParseUser.logOut();
            updateDetail();

        }
    });
    return rootView;


  }

public void updateDetail() {
    Intent intent = new Intent(getActivity(), MainActivity.class);
    startActivity(intent);
}
}

我想打开这个 MainFragment 到 MainActivity。

我试过这个：

FragmentManager fm = getFragmentManager(); fm.beginTransaction().replace(R.id.content_frame,new MainFragments()).commit();

如果 MainFragment 扩展了 Fragment 但我的 ListView 不起作用...

您的帮助将不胜感激！ 问候， 马旺

Answer 1

ListFragment 有两个版本。一个内置在框架中（android.app.ListFragment），一个是支持库的一部分（android.support.v4.app.ListFragment）。

使用支持库版本，您可以定位在引入 Fragments 之前的 Android 版本。你有两个选择：

如果您想继续使用支持库版本以获得最大兼容性，您需要更改您在 Activity 中使用的 FragmentManager，方法是：

FragmentManager fm = getSupportFragmentManager();

或者，如果您想使用框架版本，您只需将片段中的导入语句更改为：

import android.app.ListFragment;