java - 错误 : This fragment should provide a default constructor (a public constructor with no arguments)

Question

我的类像这样扩展 DialogFragment:

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");
    }

然后这样调用:

    <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 强制您获得一个空的、无参数的构造函数。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 中，Android 将重新创建您的 fragment 并调用默认构造函数。

对于这种情况，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 是可打包的，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]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 fragment 中使用非默认构造函数来停止应用程序的构建。