java - 我在 OnResume() 而不是 OnCreate() 中有必要的代码，但是当我转到不同的 Activity 然后返回时，ListView 中的数组数据仍然消失

Question

正如标题所示，当我离开 Activity 然后返回时，我的 ListView 消失。我搜索了其他问题，发现我遇到了问题，因为一切都在 OnCreate() 中。我将其移至 OnResume()，但我的应用程序绝对没有任何变化。

我删除了一些不相关的东西，因为它说我的代码太多了，所以如果一些括号搞乱了，那就是原因。我在 AndroidStudio 中没有收到任何括号错误。

这是我的代码:

public class Income extends MainActivity {

    EditText enterIncomeEditText;
    EditText enterIncomeNamesEditText;
    Button addIncomeButton;
    ListView incomeAmountListView;
    ListView incomeNameListView;

    // new String Array for listview
    private String[] incomeArray;
    //create getter
    public String[] getIncomeArray() {
        return  incomeArray;
    }

    //new string array for listview names
    private String[] incomeNames;


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

        //initialize new String array
        incomeArray = new String[]{
                ""
        };

        //initialize new String Array for listview
        incomeNames = new String[]{
                ""
        };

        //connect EditTexts
        enterIncomeEditText = findViewById(R.id.enter_income_edit_text);
        enterIncomeNamesEditText = findViewById(R.id.enter_income_names_edit_text);
        addIncomeButton = findViewById(R.id.add_income_button);
        incomeAmountListView = findViewById(R.id.income_amount_list_view);
        incomeNameListView = findViewById(R.id.income_name_list_view);
    }

    //override onResume so things don't get deleted each time the activity changes
    @Override
    protected void onResume() {
        super.onResume();

        // Create a List from String Array elements
        final List<String> income_list = new ArrayList<>(Arrays.asList(incomeArray));

        // Create an ArrayAdapter from List
        final ArrayAdapter<String> arrayAdapter = new ArrayAdapter<>
                (this, android.R.layout.simple_list_item_1, income_list);

        //Bind ListView with ArrayAdapter items
        incomeAmountListView.setAdapter(arrayAdapter);


        // Create a List from String Array elements
        final List<String> income_names_list = new ArrayList<>(Arrays.asList(incomeNames));

        // Create an ArrayAdapter from List
        final ArrayAdapter<String> arrayAdapterNames = new ArrayAdapter<>
                (this, android.R.layout.simple_list_item_1, income_names_list);

        //Bind ListView with ArrayAdapter items
        incomeNameListView.setAdapter(arrayAdapterNames);

        //add everything for navigation drawer
        mDrawerLayout = findViewById(R.id.drawer_layout);

        addIncomeButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                if (TextUtils.isEmpty(enterIncomeEditText.getText()) ||
                        TextUtils.isEmpty(enterIncomeNamesEditText.getText())) {
                    Toast.makeText(Income.this, "Income Name or Amount Empty", Toast.LENGTH_SHORT).show();
                } else {
                    String income = enterIncomeEditText.getText().toString() + "\n";
                    String incomeName = enterIncomeNamesEditText.getText().toString() + "\n";
                    //add new expenses to list and notify data set changed
                    income_list.add(income);
                    income_names_list.add(incomeName);

                    arrayAdapter.notifyDataSetChanged();
                    arrayAdapterNames.notifyDataSetChanged();
                }
                enterIncomeNamesEditText.setText("");
                enterIncomeEditText.setText("");
        });
    }
}

Answer 1

要在处理其他 Activity 时保留当前 Activity 的数据，您需要覆盖

public void onSaveInstanceState(Bundle outState)

您的 Activity 中的方法，将所有数据保存在 bundle 中。这样，如果您转到另一个 Activity ，您的数据会保留在 bundle 中，当您按返回时，您可以使用另一种方法检索数据

public void onRestoreInstanceState(Bundle savedInstanceState) 

然后，您可以从此 bundle 中取回数据，并将其显示在您的 Activity 中。

希望这对您有帮助。