Java 嵌套片段中的findViewById

我试图以片段（R.layout.fragment_2_ble）而不是主活动布局（R.layout.Activity_main）显示活动处理的结果

因此，当我试图查找（R.id.devicelist）时，我遇到了一个问题，它位于fragment_2_ble中，而不在activity_main中

MainActivity.java：

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


    //setButtonText();

    ble_device_list_adapter = new ListAdapter();

    ListView listView = (ListView) this.findViewById(R.id.deviceList);
    listView.setAdapter(ble_device_list_adapter);

    ble_scanner = new BLEScanner();

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {

            if (ble_scanning) {
                ble_scanner.stopScanning();
            }

            BluetoothDevice device = ble_device_list_adapter.getDevice(position);
            if (toast != null) {
                toast.cancel();
            }
            Intent intent = new Intent(MainActivity.this, PeripheralControlActivity.class);
            intent.putExtra(PeripheralControlActivity.EXTRA_NAME, device.getName());
            intent.putExtra(PeripheralControlActivity.EXTRA_ID, device.getAddress());
            startActivity(intent);

        }
    });


    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);

    displaySelectedScreen(R.id.nav_data);

    //ButterKnife.bind(this);
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
    boolean logged = prefs.getBoolean("logged", false);
    if (!logged) {
        //Launch login activity
        Intent intent = new Intent(this, LoginActivity.class);
        startActivity(intent);
    }
}

@Override
protected void onStart() {
    super.onStart();
}

private void displaySelectedScreen(int itemId) {

    //creating fragment object
    Fragment fragment = null;

    //initializing the fragment object which is selected
    switch (itemId) {
        case R.id.nav_data:
            fragment = new DataFragment();
            break;
        case R.id.nav_BLE:
            fragment = new BLEFragment();
            break;
        case R.id.nav_settings:
            fragment = new SettingsFragment();
            break;
    }

    //replacing the fragment
    if (fragment != null) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(R.id.content_frame, fragment);
        ft.commit();
    }

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


@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    displaySelectedScreen(item.getItemId());
    return true;
}

---

有没有关于如何修复此问题的想法？

在片段

onCreateView（）

中，您将看到如下内容：

YOURLISTVIEW = (ListView) view.findViewById(R.id.deviceList);

public ListView getListView(){
    return YOURLISTVIEW;
}

public class BLEFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        //returning our layout file
        View view = inflater.inflate(R.layout.fragment_2_ble, container, false);
        ListView list = (ListView) view.findViewById(R.id.your_id);
        list.setOnClickListenre(...);
        return view;
    }
}

在片段内部，您可以创建如下方法：

YOURLISTVIEW = (ListView) view.findViewById(R.id.deviceList);

public ListView getListView(){
    return YOURLISTVIEW;
}

public class BLEFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        //returning our layout file
        View view = inflater.inflate(R.layout.fragment_2_ble, container, false);
        ListView list = (ListView) view.findViewById(R.id.your_id);
        list.setOnClickListenre(...);
        return view;
    }
}

然后主要是你会有一个片段的实例

myFragment.getListView();

您可以从片段访问

列表视图

myFragment.getListView();

---

我要补充的是，如果此活动是片段的父级，那么

findViewById（R.id.fragmentITEM）

应该可以工作。

默认情况下，您无法实现这种结构。在创建时的活动中找不到片段UI元素

因为在“活动”中创建onCreate视图时未创建片段UI元素

---

您可以在这个链接中找到简短的答案：

我认为您缺少关于片段的概念。 如果listView在片段中，则应在片段中创建findViewById并设置OnClickListener。就这样,

YOURLISTVIEW = (ListView) view.findViewById(R.id.deviceList);

public ListView getListView(){
    return YOURLISTVIEW;
}

public class BLEFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        //returning our layout file
        View view = inflater.inflate(R.layout.fragment_2_ble, container, false);
        ListView list = (ListView) view.findViewById(R.id.your_id);
        list.setOnClickListenre(...);
        return view;
    }
}

---

为什么要在活动中使用ListView，而在片段中使用它？用碎片来处理它。