Class Cast Exception 从子片段中检索选择的日期以显示在父片段中
Class Cast Exception retrieving Chosen date from childfragment to show in parent fragment
我有一个名为 Planning 的 parentfragment，我想在其中显示一个名为 DatePickerfragment 的 DialogFragment。DatePickerFragment 有一个 button 单击时，将为用户显示 datepicker。用户选择一个日期，该日期应传递给名为 'date'.
的文本视图中的 Parent Fragment
不幸的是，每次我点击 button 应用程序都会崩溃并出现以下错误：
java.lang.ClassCastException: com.example.android.meat_timealpha10.Activities.MainActivity cannot be cast to android.app.DatePickerDialog$OnDateSetListener
at com.example.android.meat_timealpha10.Fragments.DatePickerFragment.onCreateDialog(DatePickerFragment.java:29)
我知道错误在哪里，但我不知道如何解决。
它指的是 DatePickerDialogFragment:
中的这一行
return new DatePickerDialog(getActivity(), (DatePickerDialog.OnDateSetListener)getActivity(), year, month, day );
问题是我关注了一个 youtube 视频，那个人似乎没有任何问题。再说一次，他不像我一样使用 nested fragments 。
有谁知道如何修复该错误以便所选日期显示在 textview?
这是我的代码：
XML，共 parent fragment：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".Fragments.planning">
<Button
android:id="@+id/chooseDate"
style="@style/Widget.AppCompat.Button.Borderless.Colored"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginBottom="5dp"
android:elevation="0dp"
android:hint="touch here to select date"
android:textSize="20sp" />
<TextView
android:id="@+id/date"
android:layout_width="match_parent"
android:layout_height="30dp"
android:textColor="@color/blue" />
</LinearLayout>
以下是Child Fragment DatePickerFragment：
package com.example.android.meat_timealpha10.Fragments;
import android.app.DatePickerDialog;
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.DialogFragment;
import android.widget.DatePicker;
import android.widget.TextView;
import com.example.android.meat_timealpha10.R;
import org.w3c.dom.Text;
import java.text.DateFormat;
import java.util.Calendar;
public class DatePickerFragment extends DialogFragment {
public String dateHolder;
@NonNull
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
Calendar c = Calendar.getInstance();
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int day = c.get(Calendar.DAY_OF_MONTH);
return new DatePickerDialog(getActivity(), (DatePickerDialog.OnDateSetListener)getActivity(), year, month, day );
}
}
parent fragment 的代码（没有导入）
public class planning extends Fragment implements DatePickerDialog.OnDateSetListener{
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
public planning() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment planning.
*/
// TODO: Rename and change types and number of parameters
public static planning newInstance(String param1, String param2) {
planning fragment = new planning();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_planning,
container, false);
final Button chooseDate = (Button)view.findViewById(R.id.chooseDate);
chooseDate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
DialogFragment datePicker = new DatePickerFragment();
datePicker.show(getChildFragmentManager(), "date picker");
}
});
return view;
}
@Override
public void onDateSet(DatePicker view, int year, int month, int day) {
Calendar c = Calendar.getInstance();
c.set(Calendar.YEAR, year);
c.set(Calendar.MONTH, month);
c.set(Calendar.DAY_OF_MONTH, day);
String currentDateString = DateFormat.getDateInstance(DateFormat.FULL).format(c.getTime());
TextView date = (TextView)view.findViewById(R.id.date);
date.setText(currentDateString);
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
我在这方面还很陌生，所以在回答我的问题时请尽量让它足够容易理解。
在此先感谢大家！
正如它所建议的那样，你不能将activity转换为监听器，错误出现在这一行：(DatePickerDialog.OnDateSetListener)getActivity().
您需要在片段中实现 DatePickerDialog.OnDateSetListener 并覆盖 onDateSet 函数：
public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener {
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
...
return new DatePickerDialog(getActivity(), this, year, month, day);
}
@Override
public void onDateSet(DatePicker view, int year, int month, int day) {
...
}}
我有一个名为 Planning 的 parentfragment，我想在其中显示一个名为 DatePickerfragment 的 DialogFragment。DatePickerFragment 有一个 button 单击时，将为用户显示 datepicker。用户选择一个日期，该日期应传递给名为 'date'.
Parent Fragment
不幸的是，每次我点击 button 应用程序都会崩溃并出现以下错误：
java.lang.ClassCastException: com.example.android.meat_timealpha10.Activities.MainActivity cannot be cast to android.app.DatePickerDialog$OnDateSetListener
at com.example.android.meat_timealpha10.Fragments.DatePickerFragment.onCreateDialog(DatePickerFragment.java:29)
我知道错误在哪里，但我不知道如何解决。
它指的是 DatePickerDialogFragment:
return new DatePickerDialog(getActivity(), (DatePickerDialog.OnDateSetListener)getActivity(), year, month, day );
问题是我关注了一个 youtube 视频，那个人似乎没有任何问题。再说一次，他不像我一样使用 nested fragments 。
有谁知道如何修复该错误以便所选日期显示在 textview?
这是我的代码：
XML，共 parent fragment：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".Fragments.planning">
<Button
android:id="@+id/chooseDate"
style="@style/Widget.AppCompat.Button.Borderless.Colored"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginBottom="5dp"
android:elevation="0dp"
android:hint="touch here to select date"
android:textSize="20sp" />
<TextView
android:id="@+id/date"
android:layout_width="match_parent"
android:layout_height="30dp"
android:textColor="@color/blue" />
</LinearLayout>
以下是Child Fragment DatePickerFragment：
package com.example.android.meat_timealpha10.Fragments;
import android.app.DatePickerDialog;
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.DialogFragment;
import android.widget.DatePicker;
import android.widget.TextView;
import com.example.android.meat_timealpha10.R;
import org.w3c.dom.Text;
import java.text.DateFormat;
import java.util.Calendar;
public class DatePickerFragment extends DialogFragment {
public String dateHolder;
@NonNull
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
Calendar c = Calendar.getInstance();
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int day = c.get(Calendar.DAY_OF_MONTH);
return new DatePickerDialog(getActivity(), (DatePickerDialog.OnDateSetListener)getActivity(), year, month, day );
}
}
parent fragment 的代码（没有导入）
public class planning extends Fragment implements DatePickerDialog.OnDateSetListener{
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
public planning() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment planning.
*/
// TODO: Rename and change types and number of parameters
public static planning newInstance(String param1, String param2) {
planning fragment = new planning();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_planning,
container, false);
final Button chooseDate = (Button)view.findViewById(R.id.chooseDate);
chooseDate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
DialogFragment datePicker = new DatePickerFragment();
datePicker.show(getChildFragmentManager(), "date picker");
}
});
return view;
}
@Override
public void onDateSet(DatePicker view, int year, int month, int day) {
Calendar c = Calendar.getInstance();
c.set(Calendar.YEAR, year);
c.set(Calendar.MONTH, month);
c.set(Calendar.DAY_OF_MONTH, day);
String currentDateString = DateFormat.getDateInstance(DateFormat.FULL).format(c.getTime());
TextView date = (TextView)view.findViewById(R.id.date);
date.setText(currentDateString);
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
我在这方面还很陌生，所以在回答我的问题时请尽量让它足够容易理解。 在此先感谢大家！
正如它所建议的那样，你不能将activity转换为监听器，错误出现在这一行：(DatePickerDialog.OnDateSetListener)getActivity().
您需要在片段中实现 DatePickerDialog.OnDateSetListener 并覆盖 onDateSet 函数：
public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener {
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
...
return new DatePickerDialog(getActivity(), this, year, month, day);
}
@Override
public void onDateSet(DatePicker view, int year, int month, int day) {
...
}}