java - 为什么 ListView 没有保存到内存中？

Question

我的应用程序有问题。有一个带有自定义对象的 ListView，我希望它保存在内存中，并能够在应用程序运行时在其中添加新的东西。问题是我不知道如何将我的 ListView 保存在内存中并显示它。你能帮忙吗？

public class MainActivity extends AppCompatActivity {


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

        String nume;
        String prenume;
        String email;
        String eticheta;
        int number;

        TextView addColegButton = findViewById(R.id.textView3);
        ListView nume_ListView = findViewById(R.id.ListView);

        String nou = getString(R.string.nou);
        String addClassmate = getString(R.string.AddClassmate);

        TextView buna = findViewById(R.id.bunaTextView);
        Calendar calendar = Calendar.getInstance();
        int hour = calendar.get(Calendar.HOUR_OF_DAY);


        if (hour >= 12 && hour <= 18) {
            buna.setText(R.string.bună);
            buna.setTextSize(43);
        }
        if (hour >= 18 && hour <= 24) {
            buna.setText(R.string.bunăSeara);
            buna.setTextSize(39);
        }
        if (hour >= 0 && hour <= 12) {
            buna.setText(R.string.bunăDimi);
            buna.setTextSize(36);
        }

        ArrayList<nume_list> colegi_list = DataHolder.getInstance().people;

        ColegListAdapter adapter1 = new ColegListAdapter(this, R.layout.list_item_layout, colegi_list);
        nume_ListView.setAdapter(adapter1);


        if (savedInstanceState == null) {
            Bundle extras = getIntent().getExtras();
            if (extras == null) {
                nume = null;
                prenume = null;
                eticheta=null;
                email=null;
                number= 0;
            } else {
                nume = extras.getString("NumeFam");
                prenume = extras.getString("Prenume");
                email = extras.getString("Email");
                number = extras.getInt("Number");
                eticheta = extras.getString("Eticheta");
                String nume_complet = prenume + " " + nume;

                nume_list colegNou = new nume_list(nume_complet, eticheta, email, number);
                nume_list colegNouv2 = new nume_list(prenume, eticheta, email, number);

                LayoutInflater inflater = getLayoutInflater();
                View layout = inflater.inflate(R.layout.toast_custom,
                        (ViewGroup) findViewById(R.id.custom_toast_container));

                TextView text = (TextView) layout.findViewById(R.id.textToast);

                Toast toast = new Toast(getApplicationContext());
                toast.setGravity(Gravity.TOP | Gravity.CENTER_HORIZONTAL,0,50);
                toast.setView(layout);

                if (prenume != null && nume != null && eticheta != null) {
                    colegi_list.add(colegNou);
                    text.setText(R.string.toast1);
                    toast.show();
                }

                else if (nume == null && eticheta != null && prenume != null) {
                    colegi_list.add(colegNouv2);
                    text.setText(R.string.toast1);
                    toast.show();
                }

                else{
                    text.setText(R.string.toast2);
                    toast.show();
                }

            }
        } else {
            SharedPreferences sharedPreferences = getApplicationContext().getSharedPreferences("Schoolbox", MODE_PRIVATE);

            nume = sharedPreferences.getString("NumeFam", "");
            prenume = sharedPreferences.getString("Prenume","");
            eticheta = sharedPreferences.getString("Eticheta","");
            email = sharedPreferences.getString("Email","");
            number =sharedPreferences.getInt("Number",0);

            String nume_complet = prenume + " " + nume;
            nume_list colegNou = new nume_list(nume_complet, eticheta, email, number);
            nume_list colegNouv2 = new nume_list(prenume, eticheta, email, number);

            LayoutInflater inflater = getLayoutInflater();
            View layout = inflater.inflate(R.layout.toast_custom,
                    (ViewGroup) findViewById(R.id.custom_toast_container));

            TextView text = (TextView) layout.findViewById(R.id.textToast);

            Toast toast = new Toast(getApplicationContext());
            toast.setGravity(Gravity.TOP | Gravity.CENTER_HORIZONTAL,0,50);
            toast.setView(layout);

            if (prenume != null && nume != null && eticheta != null) {
                colegi_list.add(colegNou);
                text.setText(R.string.toast1);
                toast.show();
            }

            else if (nume == null && eticheta != null && prenume != null) {
                colegi_list.add(colegNouv2);
                text.setText(R.string.toast1);
                toast.show();
            }

            else{
                text.setText(R.string.toast2);
                toast.show();
            }
        }

        addColegButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, ColegInfoActivity.class);
                startActivity(intent, ActivityOptions.makeSceneTransitionAnimation(MainActivity.this).toBundle());
            }
        });



        //TODO: Create the new classmate activity and set OnClickListener for the button to it.
    }
}

THE DETAILS ACTIVITY JAVA 代码（详细信息被添加到一个新对象，稍后在 ListView 中添加一个新项目）

Intent intent1 = new Intent(ColegInfoActivity.this, MainActivity.class);
                Bundle extras = new Bundle();
                extras.putString("Prenume", prenumeString);
                extras.putString("NumeFam", numeFamString);
                extras.putString("Eticheta",etichetaString);
                extras.putString("Email", emailString);
                extras.putInt("Number",number2);
                SharedPreferences sharedPreferences = getApplicationContext().getSharedPreferences("Schoolbox", MODE_PRIVATE);
                sharedPreferences.edit().putString("Prenume", prenumeString).apply();
                sharedPreferences.edit().putString("NumeFam", numeFamString).apply();
                sharedPreferences.edit().putString("Eticheta",etichetaString).apply();
                sharedPreferences.edit().putString("Email", emailString).apply();
                sharedPreferences.edit().putInt("Number",number2).apply();

标签： javaandroid