无法从 activity 获取包值到片段

Question

请帮忙，我刚学会 android，我正在尝试使用 bundle 将数据从 Main Activity 发送到片段。这是 MainActivity

的代码

@Override
    public boolean onQueryTextChange(String newText) {

    if (newText.length()>0){
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        Bundle bundle = new Bundle();
        bundle.putString("query", newText);
        SearchMovieFragment searchMovieFragment = new SearchMovieFragment();
        searchMovieFragment.setArguments(bundle);
        transaction.replace(R.id.frame_container, searchMovieFragment);
        transaction.commit();
     }

这是我片段中的代码

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    String query = getArguments().getString("query");
    MoviesViewModel moviesViewModel = ViewModelProviders.of(this).get(MoviesViewModel.class);
    moviesViewModel.setSearchedMovie(query);
    moviesViewModel.getMovie().observe(this, getListMovies);

    return inflater.inflate(R.layout.fragment_movies, container, false);
}

这一行发生错误String query = getArguments().getString("query"); 错误是

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference

我该如何解决这个问题？

这是我的主要内容Activity

public class MainActivity extends AppCompatActivity {

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

    SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());
    ViewPager viewPager = findViewById(R.id.view_pager);
    viewPager.setAdapter(sectionsPagerAdapter);
    TabLayout tabs = findViewById(R.id.tabs);
    tabs.setupWithViewPager(viewPager);

    ActionBar actionBar = getSupportActionBar();
    if(actionBar != null){
        actionBar.setBackgroundDrawable(getResources().getDrawable(R.drawable.color_primary_gradient));
    }

    getSupportActionBar().setElevation(0);
}

protected void setStatusBarGradiant(Activity activity) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        Window window = activity.getWindow();
        Drawable background = activity.getResources().getDrawable(R.drawable.color_primary_gradient);
        window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
        window.setStatusBarColor(activity.getResources().getColor(android.R.color.transparent));
        window.setBackgroundDrawable(background);
    }
}

private void loadFragment(Fragment fragment) {
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.frame_container, fragment);
    transaction.commit();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main_menu, menu);

    if(menu instanceof MenuBuilder){
        MenuBuilder m = (MenuBuilder) menu;
        m.setOptionalIconsVisible(true);
    }

    final SearchManager searchManager = (SearchManager) getSystemService(Context.SEARCH_SERVICE);

    if (searchManager != null) {
        final SearchView searchView = (SearchView) (menu.findItem(R.id.search)).getActionView();
        searchView.setSearchableInfo(searchManager.getSearchableInfo(getComponentName()));

        searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {

            @Override
            public boolean onQueryTextSubmit(String query) {
                searchView.clearFocus();
                return true;
            }

            @Override
            public boolean onQueryTextChange(String newText) {

                if (newText.length()>0){
                    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
                    Bundle bundle = new Bundle();
                    bundle.putString("query", newText);
                    SearchMovieFragment searchMovieFragment = new SearchMovieFragment();
                    searchMovieFragment.setArguments(bundle);
                    getSupportFragmentManager().beginTransaction().replace(R.id.frame_container,searchMovieFragment).commit(); 
                }
                else {
                    loadFragment(new SearchMovieFragment());
                }
                return true;
            }
        });
    }
    return true;
}

}

和我的 SearchMovieFragment

public class SearchMovieFragment extends Fragment {
private RecyclerView rvMovies;
private ArrayList<Movie> list = new ArrayList<>();
private CardViewMovieAdapter adapter;
private ProgressBar progressBar;
private String query;

public SearchMovieFragment() {
    // Required empty public constructor
}

private Observer<ArrayList<Movie>> getListMovies = new Observer<ArrayList<Movie>>() {
    @Override
    public void onChanged(ArrayList<Movie> movies) {
        if (movies != null) {
            adapter.setData(movies);
        }
        else {
            Toast.makeText(getContext(), R.string.no_result, Toast.LENGTH_LONG).show();
        }
        showLoading(false);
    }
};

private static final String ARG_PARAM1 = "query";
public static SearchMovieFragment newInstance(String param1) {
    SearchMovieFragment fragment = new SearchMovieFragment();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    fragment.setArguments(args);
    return fragment;
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    query = getArguments().getString("query");
    return inflater.inflate(R.layout.fragment_movies, container, false);
}


public void onViewCreated(View view, Bundle savedInstanceState) {
    rvMovies = view.findViewById(R.id.rv_movies);
    rvMovies.setHasFixedSize(true);
    progressBar = view.findViewById(R.id.progressBar);

    MoviesViewModel moviesViewModel = ViewModelProviders.of(this).get(MoviesViewModel.class);
    moviesViewModel.setSearchedMovie(query);
    moviesViewModel.getMovie().observe(this, getListMovies);

    showLoading(true);
    showRecyclerCardView();
}

private void showRecyclerCardView() {
    rvMovies.setLayoutManager(new LinearLayoutManager(this.getContext()));
    adapter = new CardViewMovieAdapter(list);
    rvMovies.setAdapter(adapter);
}

}

Answer 1

来自Activity：

Bundle bundle = new Bundle();
bundle.putString("value", "values From Activity");
// set SearchMovieFragment Arguments
SearchMovieFragment searchMovieFragment = new SearchMovieFragment();
searchMovieFragment.setArguments(bundle);

并且在您的片段 onCreateView 中：

    @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    String strValue = getArguments().getString("value");    
    return inflater.inflate(R.layout.fragment, container, false);
}

Answer 2

activity

可以直接传newInstance(value)中的值

@Override
    public boolean onQueryTextChange(String newText) {

    if (newText.length()>0){
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        SearchMovieFragment searchMovieFragment = new SearchMovieFragment.newInstance(newText);
        transaction.replace(R.id.frame_container, searchMovieFragment);
        transaction.commit();
     } else {
         loadFragment(new SearchMovieFragment.newInstance(""));   // pass blank string to avoid null exception in fragment
     }

片段

在片段

中创建newInstance

private static final String ARG_PARAM1 = "query";
      public static SearchMovieFragment newInstance(String param1) {
        SearchMovieFragment fragment = new SearchMovieFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        fragment.setArguments(args);
        return fragment;
    }

      
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    String query = getArguments().getString(ARG_PARAM1);
    MoviesViewModel moviesViewModel = ViewModelProviders.of(this).get(MoviesViewModel.class);
    moviesViewModel.setSearchedMovie(query);
    moviesViewModel.getMovie().observe(this, getListMovies);

    return inflater.inflate(R.layout.fragment_movies, container, false);
}

Answer 3

你能试试删除这个吗？

private static final String ARG_PARAM1 = "query";
public static SearchMovieFragment newInstance(String param1) {
    SearchMovieFragment fragment = new SearchMovieFragment();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    fragment.setArguments(args);
    return fragment;
}

希望对你有用

Answer 4

好吧，我对您的 onQueryTextChange 方法进行了如下更改。我可以从您发布的内容中找出的唯一问题是 loadFragment(new SearchMovieFragment());，因为它会抛出 NPE，因为在这种情况下您没有向片段添加参数，因此 getArguments() 将为空。

public boolean onQueryTextChange(String newText) {
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    SearchMovieFragment searchMovieFragment = new SearchMovieFragment();
    Bundle bundle = new Bundle();
    if(newText.length()>0) {
        bundle.putString("query", newText);
    } else {
        bundle.putString("query", "");
    }
    searchMovieFragment.setArguments(bundle);
    transaction.replace(R.id.frame_container,searchMovieFragment);
    transaction.commit();
    return true;
}

检查这是否有任何帮助，否则请确保没有其他地方您在不添加参数的情况下创建了该片段的实例。

无法从 activity 获取包值到片段

Cant get bundle value from activity to fragment

java

android

bundle

android-fragments