Question

我创建了一个更新类变量的类。我正在创建该类的新实例，然后尝试调用get方法。但我得到一个'无法解决方法错误，我不明白为什么。

public static class DatePickerFragment extends DialogFragment
    implements DatePickerDialog.OnDateSetListener {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        // Use the current date as the default date in the picker
        final Calendar c = Calendar.getInstance();
        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);
    }
    int selectedDate;
    public void onDateSet(DatePicker view, int year, int month, int day) {
        // Do something with the date chosen by the user
        selectedDate = day+month+year;
    }
    public int getSelectedDate() {
        return selectedDate;
    }

}
public void showDatePickerDialog(View view) {
    DialogFragment newFragment = new DatePickerFragment();
    newFragment.show(getFragmentManager(), "datePicker");
    int output = newFragment.getSelectedDate();
}

Answer 1

错误在这里：

public void showDatePickerDialog(View view) {
   DialogFragment newFragment = new DatePickerFragment();
   newFragment.show(getFragmentManager(), "datePicker");
   int output = newFragment.getSelectedDate();
}

您的变量newFragment是DialogFragment。因此，您必须强制转换变量或更改声明：

DatePickerFragment newFragment = new DatePickerFragment();

或

int output = ((DatePickerFragment)newFragment).getSelectedDate();

编辑：要获取所选日期，您必须使用Listener而不是同步方法。所以你必须改变你的代码：

public static class DatePickerFragment extends DialogFragment
implements DatePickerDialog.OnDateSetListener {
private MyListener listener;
public DatePickerFragment(MyListener listener){
   this.listener = listener;
}

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    // Use the current date as the default date in the picker
    final Calendar c = Calendar.getInstance();
    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);
}
int selectedDate;
public void onDateSet(DatePicker view, int year, int month, int day) {
    // Do something with the date chosen by the user
    selectedDate = day+month+year;
    if(listener!=null){
        listener.theDateHasChanged(selectedDate);
    }
}
public int getSelectedDate() {
    return selectedDate;
}

然后您的活动必须实施MyListener界面并实施theDateHasChanged，最后您必须从fragment实例化activity所以：

DatePickerFragment newFragment = new DatePickerFragment(this);

Answer 2

也许那是因为你的班级是静态的。在java中，您无法创建定义为static的类的实例。对于静态类，可以使用直接调用方法。（）;

DatePickerFragment.show(getFragmentManager(),"datePicker");

希望这会有所帮助。：）

无法从类实例Android调用方法

2 个答案: