Android Fragment 的使用小结

public class MyFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // 膨胀 fragment 的布局
        return inflater.inflate(R.layout.fragment_my, container, false);
    }
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        // 在这里初始化视图和逻辑
    }
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello Fragment!" />
</LinearLayout>

<!-- activity_main.xml -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <fragment
        android:id="@+id/myFragment"
        android:name="com.example.MyFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // 检查是否已经添加了Fragment（防止旋转时重复添加）
        if (savedInstanceState == null) {
            // 创建Fragment实例
            MyFragment fragment = new MyFragment();
            // 开始Fragment事务
            getSupportFragmentManager().beginTransaction()
                .add(R.id.fragment_container, fragment) // 添加到容器
                .commit();
        }
    }
}

<FrameLayout
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

// 替换Fragment
getSupportFragmentManager().beginTransaction()
    .replace(R.id.fragment_container, new AnotherFragment())
    .addToBackStack(null) // 允许用户按返回键返回上一个Fragment
    .commit();

// 在Fragment中
if (getActivity() instanceof MyActivityInterface) {
    ((MyActivityInterface) getActivity()).doSomething();
}
// Activity实现接口
public interface MyActivityInterface {
    void doSomething();
}

MyFragment fragment = (MyFragment) getSupportFragmentManager()
    .findFragmentById(R.id.my_fragment);
if (fragment != null) {
    fragment.doSomethingInFragment();
}

// 创建共享ViewModel
public class SharedViewModel extends ViewModel {
    private final MutableLiveData<String> selected = new MutableLiveData<>();
    public void select(String item) {
        selected.setValue(item);
    }
    public LiveData<String> getSelected() {
        return selected;
    }
}
// 在Activity或Fragment中获取
SharedViewModel model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
model.getSelected().observe(this, item -> {
    // 更新UI
});

// 创建Fragment时传递参数
public static MyFragment newInstance(String param) {
    MyFragment fragment = new MyFragment();
    Bundle args = new Bundle();
    args.putString("key", param);
    fragment.setArguments(args);
    return fragment;
}
// 在Fragment中获取参数
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        String param = getArguments().getString("key");
    }
}

// 在build.gradle中添加依赖
implementation "androidx.navigation:navigation-fragment:2.3.5"
// 使用NavController导航
NavController navController = Navigation.findNavController(view);
navController.navigate(R.id.action_to_next_fragment);