[英]Error:Error: This class should provide a default constructor (a public constructor with no arguments)
[英]Error: This fragment should provide a default constructor (a public constructor with no arguments)
我的课程像这样扩展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");
}
并像这样调用:
<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)
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,尝试忽略配置build.gradle
这些错误,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。
您需要删除此构造函数
public DatePickerFragment(EditText editText) {
editDate = editText;
}
您不应将视图引用传递给Fragment。 如果要在Activity或其他地方更新EditText,请使用侦听器。
public DatePickerFragment() {}
@Override
public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
dateTime.set(year, monthOfYear, dayOfMonth);
// editDate.setText(dateFormatter
// .format(dateTime.getTime()));
Intent intent = new Intent();
intent.setAction("CUSTOM_INTENT_FOR_SETTING_EDITTEXT");
Bundle bundle = new Bundle();
bundle.putString("my_data", dateTime.getTime.toString());
intent.putExtras(bundle);
sendBroadcast(intent);
}
public class SubmitFragment extends Fragment {
View view;
EditText editDate;
String strDate;
Button btnSubmit;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_submit, container, false);
editDate = (EditText) view.findViewById(R.id.editDate);
btnSend = (Button) view.findViewById(R.id.buttonSend);
btnSend.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
strDate = editDate.getText().toString();
Log.v("strDate..... >>>", strDate);
}
});
return view;
}
// Our handler for received Intents. This will be called whenever an Intent
// with an action named "CUSTOM_INTENT_FOR_SETTING_EDITTEXT" is broadcasted.
private BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
// Get extra data included in the Intent
String message = intent.getStringExtra("my_data");
Log.d("receiver", "message: " + message);
*****// Use this message to set Edittext here...*****
}
};
@Override
protected void onPause() {
// Unregister since the activity is about to be closed.
LocalBroadcastManager.getInstance(getactivity()).unregisterReceiver(mMessageReceiver);
super.onDestroy();
}
@Override
protected void onResume() {
// register the receiver here..
super.onResume(); LocalBroadcastManager.getInstance(getactivity()).registerReceiver(mMessageReceiver,
new IntentFilter("CUSTOM_INTENT_FOR_SETTING_EDITTEXT"));
}
}
希望这有帮助..我在这里做的正是使用localBroadcast来做必要的事情。另一种方法是使用settext的接口但是这个方法的一个错误的事情是,当应用程序在后台工作了这么久,它再次调用oncreateview时将返回null。
添加@SuppressLint(“ValidFragment”)
在你上课之前,
公共类DatePickerFragment扩展
我希望它对你有所帮助
看看官方文档:Fragment: https<\/a> : \/\/developer.android.com\/reference\/android\/app\/Fragment<\/a>
Fragment 的所有子类都必须包含一个公共的无参数构造函数。 框架通常会在需要时重新实例化一个片段类,特别是在状态恢复期间,并且需要能够找到这个构造函数来实例化它。 如果无参数构造函数不可用,在状态恢复过程中某些情况下会发生运行时异常。
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