为DialogFragment扩展MaterialDatePicker

Question

我想从DatePickerDialog迁移到MaterialDatePicker.在从MaterialDatePicker调用getDialog时遇到了问题，对话框的结果总是为null。

这是一个错误，还是MaterialDatePicker不支持的特性？

DatePickerDialog

private static class BirthDateUpdater extends DialogFragment implements DatePickerDialog.OnDateSetListener {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        // create calendar instance
        final Calendar c = Calendar.getInstance();

        // set calendar to birthdate
        c.setTimeInMillis(getBirthDate().getTime());

        int year = c.get(Calendar.YEAR);
        int month = c.get(Calendar.MONTH);
        int day = c.get(Calendar.DAY_OF_MONTH);

        // Create a new instance of DatePickerDialog and return it
        return new DatePickerDialog(getActivity(), this, year, month, day);
    }

    public void onDateSet(DatePicker view, int year, int month, int day) {
        // process date selected in here
    }
}

这里的MaterialDatePicker问题- picker.getDialog()的结果总是null吗？

public static class BirthDateUpdater extends DialogFragment implements 
    MaterialPickerOnPositiveButtonClickListener<Long>, 
    DialogInterface.OnCancelListener {
    
    private Dialog dialog;

    public BirthDateUpdater() {
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        try {
            // builder
            MaterialDatePicker.Builder<Long> builder = MaterialDatePicker.Builder.datePicker();
            builder.setTitleText("Select Date");

            // set date to BirthDate
            builder.setSelection(getBirthDate().getTime());

            // picker
            MaterialDatePicker<Long> picker = builder.build();
            
            // add event
            picker.addOnPositiveButtonClickListener(this);
            picker.addOnCancelListener(this);

            // dialog
            dialog = picker.getDialog(); // error in here (dialog is null)?

        } catch (Exception ex) {
            ex.printStackTrace();
        }
        return dialog;
    }

    @Override
    public void onPositiveButtonClick(Long selection) {
        try {
            Calendar dateSelected = Calendar.getInstance();
            dateSelected.setTimeInMillis(selection);
            
            // process date selected in here
            
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    @Override
    public void onCancel(@NonNull DialogInterface dialog) {
        dialog.dismiss();
    }
}

Answer 1

MaterialDatePicker已经是DialogFragment了。在您的示例中，picker.getDialog()返回null，因为在掩码下，DialogFragment对DialogFragment.mDialog的写值(该字段的值返回picker.getDialog())来自生命周期回调onCreateDialog()，它将在调用对话框的显示方法后被调用异步，也就是说，当您调用picker.show(fragmentManager)时，您可以从getDialog()方法获得非空值。

在您的情况下，您不应该扩展DialogFragment或MaterialDatePicker (这是最终的)，而是可以创建像birthDateUpdater这样的方法

public DialogFragment birthDateUpdater() {
            MaterialDatePicker.Builder<Long> builder = MaterialDatePicker.Builder.datePicker();
            builder.setTitleText("Select Date");

            // set date to BirthDate
            builder.setSelection(getBirthDate().getTime());

            // picker
            MaterialDatePicker<Long> picker = builder.build();
            
            // add event
            picker.addOnPositiveButtonClickListener(selection -> {
              try {
              Calendar dateSelected = Calendar.getInstance();
              dateSelected.setTimeInMillis(selection);
            
               // process date selected in here
            
               } catch (Exception ex) {
                 ex.printStackTrace();
               }
            });
            picker.addOnCancelListener(dialog -> {
               dialog.dismiss();
            });
            return picker
}

或者创建类，工厂，任何封装这个逻辑的东西。