java - 我在按钮单击侦听器中收到错误（Android Studio）

Question

我制作了一个应用程序来单独发送邮件，我试图在另一个应用程序中实现它，它给了我这个错误尝试调用虚拟方法

空对象引用上的“void android.widget.Button.setOnClickListener (android.view.View $ OnClickListener)”

我有我知道的 id 以及放置按钮和点击侦听器的方式都很好。错误能给出什么？

这是我的代码

public class ContactFragment extends Fragment  {

//public EditText mEmail;
public EditText mSubject;
public EditText mMessage;
private Button buttonSend_contact;


private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";


private String mParam1;
private String mParam2;

public ContactFragment() {

}



public static ContactFragment newInstance(String param1, String param2) {
ContactFragment fragment = new ContactFragment();
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_videos, container, false);

mMessage = view.findViewById(R.id.messageID);
mSubject = view.findViewById(R.id.subjectID);

buttonSend_contact =  view.findViewById(R.id.buttonSendMail);

buttonSend_contact.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        sendMail();
    }
});




return view;
}
private void sendMail() {

String mail = "[e-mail]";
String message = mMessage.getText().toString();
String subject = mSubject.getText().toString().trim();

//Send Mail
JavaMailAPI javaMailAPI = new JavaMailAPI(getActivity(),mail,subject,message);

javaMailAPI.execute();

}

这是我的xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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"
tools:context=".ContactFragment">

<!-- <EditText
android:id="@+id/mailID"
android:layout_margin="10dp"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="Email"/> -->

<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<EditText
    android:id="@+id/subjectID"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="10dp"
    android:hint="Subject" />

<EditText
    android:id="@+id/messageID"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="10dp"
    android:hint="Message" />

<Button
    android:id="@+id/buttonSendMail"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Button" />
</LinearLayout>


</FrameLayout>

标签： javaandroid-studiobuttonnullpointerexceptionnullreferenceexception