Question

我正在创建一个小应用，允许用户查看不同类别的大学图书。

到目前为止，在活动主抽屉中，我有几个不同的类别，应该使用listView加载布局，并在选中时从arrayAdapter填充此列表。我在其中一个布局上进行了设置和半工作，但是当我从导航抽屉更改为不同的类别时，问题出现了，listView仍然显示在屏幕上，我似乎无法弄清楚如何让它停下来。

我认为我需要使用endTransaction（），但如果我使用正确的东西，我还不确定。

我是Java和Android Studio的初学者，所以我希望我能够理解我所要求的内容。

如果需要更多代码或信息，我很乐意提供。

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.view.ViewGroup;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.Fragment;

import java.util.ArrayList;
import java.util.List;

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);

    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);

    FragmentManager fm = getSupportFragmentManager();
    fm.beginTransaction().replace(R.id.content_frame, new MainFragment()).commit();

    //loads the home screen when app launches
    displaySelectedScreen(R.id.nav_home);

}

@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);
}

private void displaySelectedScreen(int id) {

    Fragment fragment = null;

    //loads each layout inflator depending on what menu item has been clicked
    switch(id) {
        case R.id.nav_home:
            fragment = new Home();
            break;
        case R.id.nav_book:
            fragment = new All();
            break;
        case R.id.nav_sci_fi:
            fragment = new SciFi();
            break;
        case R.id.nav_fantasy:
            fragment = new Fantasy();
            break;
        case R.id.nav_dystopian:
            fragment = new Dystopian();
            break;
        case R.id.nav_about:
            fragment = new About();
            break;
        case R.id.nav_contact:
            fragment = new ContactUs();
            break;
    }

    if(fragment != null) {

        FragmentTransaction ft = getSupportFragmentManager(). beginTransaction();
        ft.replace(R.id.content_main, fragment);
        ft.commit();
    }

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

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.

    FragmentManager fm=getSupportFragmentManager();

    int id = item.getItemId();

    if (id == R.id.nav_book) {
        // Handle the camera action
    } else if (id == R.id.nav_sci_fi) {
        fm .beginTransaction().replace(R.id.content_frame, new BookFragment()).commit(); setTitle("Sci-Fi");
        //TODO: endTransaction 

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

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

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

    displaySelectedScreen(id);

    return true;
}
}

Answer 1

您的displaySelectedScreen（）函数正在使用FragmentTransaction而不是FragmentManager。尝试使用FragmentManager。

onNavigationItemSelected和beginTransaction（）遇到问题

1 个答案: