嵌套片段中的 findViewById

Question

我试图在片段 (R.layout.fragment_2_ble) 中显示 Activity 处理的结果，而不是 activity 主布局 (R.layout .activity_main).

因此，当我试图找到 fragment_2_ble 而不是 activity_main 中的 (R.id.devicelist) 时遇到问题。

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;
}

BLEFragment.java:

public class BLEFragment extends Fragment {

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    //returning our layout file
    return inflater.inflate(R.layout.fragment_2_ble, container, false);
}

知道如何解决这个问题吗？

Answer 1

在你的片段中onCreateView()你会有这样的东西：

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

在您的片段中，您可以创建这样的方法：

public ListView getListView(){
    return YOURLISTVIEW;
}

然后在 main 中你会有一个片段的实例。

您可以从片段中访问 ListView。

myFragment.getListView();

我要补充一点，如果这个 activity 是片段的父级，那么 findViewById(R.id.fragmentITEM) 应该可以。

Answer 2

默认情况下您无法实现这种结构。您无法在创建时在 activity 中找到片段 UI 元素。

在 activity 中创建 onCreate 视图时未创建 Becoz 片段 UI 元素。

您可以在 link 中找到简短的答案：Is it possible to access fragment's UI elements from activitiy's onCreate

Answer 3

我认为您缺少有关片段的概念。如果 listView 在片段中，则应在片段中创建 findViewById 并设置 OnClickListener。就像这样：

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;
    }
}

嵌套片段中的 findViewById

findViewById in nested Fragment

java

android

android-fragments

android-activity

android-fragmentactivity