错误：此片段应该提供一个默认构造函数（一个没有参数的公共构造函数）

Question

我的类扩展DialogFragment，如下所示：

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()));
    }

}

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

像这样呼唤：

    <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

Android SDK的新版本迫使您获得一个空的、无args的构造函数。现在这样做是一个很好的做法。这允许您将实例状态保存到bundle，Android将调用默认构造函数重新创建您的片段。

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() {}

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

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");

[EDIT]按照建议，尝试忽略这些配置build.gradle的错误，如下所示：

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。