java - Android - fragment 中的 java.lang.NullPointerException

Question

我是新人，我想开发一个连接到服务器的应用程序，然后显示底部栏。 为此，我使用一个 fragment (因为接下来我将有更多 fragment )，当我单击按钮时，将连接并设置底部栏可见。 我可以连接到服务器，并获得响应，但我无法显示底部栏，我有此错误:

java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“void com.roughike.bottombar.BottomBar.setVisibility(int)”

我知道它在这条线上:menu.Connecté(c.getString("id"));但我不知道如何解决它..

你能帮我吗？谢谢
这是我的代码:

public class FragmentConnexion extends Fragment {

    String ip = "http://MYIP/php";
    MainActivity menu = new MainActivity();
    TextView identifient,motdepasse;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View myView = inflater.inflate(R.layout.connexion, container, false);
        identifient = (TextView) myView.findViewById(identifiant);
        motdepasse = (TextView) myView.findViewById(mdp);

        Button connecte = (Button) myView.findViewById(button);
        connecte.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Connexion();
            }
        });
        return myView;
    }

    public void Connexion(){
        final String mPseudo= identifient.getText().toString();
        final String mMdp = motdepasse.getText().toString();
        final HttpGetRequest requete = new HttpGetRequest();

        new Thread(new Runnable() {
            @RequiresApi(api = Build.VERSION_CODES.KITKAT)
            @Override
            public void run() {
                requete.execute(ip+"/utilisateur/affichage_id.php?pseudo="+mPseudo+"&mdp="+mMdp);
                try {
                    if(requete.get() != null){
                        JSONObject jsonObj = new JSONObject(requete.get());
                        JSONArray jSon = jsonObj.getJSONArray("valeurs");
                        for (int i = 0; i < jSon.length(); i++) {
                            JSONObject c = jSon.getJSONObject(i);
                            if (!Objects.equals(c.getString("id"), "null")){
                                Log.i("ID",c.getString("id"));
                                menu.Connecté(c.getString("id"));
                            }
                        }
                    }
                }
                catch (InterruptedException | ExecutionException | JSONException e) {
                    e.printStackTrace();
                }
            }
        }).start();

    }
}

主要 Activity :

public class MainActivity extends AppCompatActivity {

String identifiant;
BottomBar bottombar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);


    BottomBar bottombar = (BottomBar) findViewById(R.id.bottomBar);
    bottombar.setVisibility(View.INVISIBLE);
    bottombar.setOnTabSelectListener(new OnTabSelectListener() {
        @Override
        public void onTabSelected(@IdRes int tabId) {
            if (tabId == R.id.tab_reveil) {

                Log.i("Reveil","Selectionné");
            }

            if (tabId == R.id.tab_whiz) {
                Log.i("Whiz","Selectionné");
            }

            if (tabId == R.id.tab_param) {
                Log.i("Paramètre","Selectionné");
            }
        }
    });


}

public void Connecté(String id){
    identifiant = id;
    bottombar.setVisibility(View.VISIBLE);
}

Answer 1

您应该使用((MainActivity)getActivity).Connect(c.getString("id"))
并将 BottomBar Bottombar = (BottomBar) findViewById(R.id.bottomBar); 更改为 bottombar = (BottomBar) findViewById(R.id.bottomBar);

fragment 中的菜单是一个new MainActivity()，因此bottombar为null