错误:此片段应提供默认构造函数(不带参数的公共构造函数)

Question

我的课程扩展DialogFragment如下:

public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener {

    EditText editDate;
    private Calendar dateTime = Calendar.getInstance();
    private SimpleDateFormat dateFormatter = new SimpleDateFormat("dd MMMM yyyy");

    public DatePickerFragment(EditText editText) {
        editDate = editText;
    }

@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);

}

@Override
public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
        dateTime.set(year, monthOfYear, dayOfMonth);
        editDate.setText(dateFormatter
                .format(dateTime.getTime()));
    }

}

这就是我在Activity中使用它的方式:

public void showDatePickerDialog(View v) {
        new DatePickerFragment((EditText) v).show(getSupportFragmentManager(), "datePicker");
    }

并且这样打电话:

    <EditText
        android:id="@+id/editDate"
        android:onClick="showDatePickerDialog" />

但我总是得到:

Error: This fragment should provide a default constructor (a public constructor with no arguments)

Answer 1

较新版本的Android SDK会强制您获得一个空的无参数构造函数.这是一个很好的做法.这允许您将实例状态保存到bundle中,Android将重新创建调用默认构造函数的片段.

在这种情况下,您有以下解决方案:

首先,创建默认构造函数:

public DatePickerFragment() {}

创建实例并通过setter方法设置EditText:

DatePickerFragment fragment = new DatePickerFragment();
fragment.setEditText(v); // create this setter
fragment.show();

由于EditText是parcelable,您还可以设置为参数:

DatePickerFragment fragment = new DatePickerFragment();
Bundle bundle = new Bundle();
bundle.putExtra("EditText", v); 
fragment.setArguments(bundle); // setArguments is a method that already exists in fragments.
fragment.show(getSupportFragmentManager(), "DatePicker");

[编辑] 根据建议,尝试忽略这样的错误配置build.gradle:

lintOptions { 
  abortOnError false 
  checkReleaseBuilds false 
} 

这不会通过在片段中使用非默认构造函数来停止应用程序的构建.

Answer 2

你需要删除这个构造函数

public DatePickerFragment(EditText editText) {
    editDate = editText;
}

您不应该将 View 引用传递给 Fragment。如果您想更新 Activity 或其他地方的 EditText，请使用侦听器。