如何在Fragment中使用“findViewById”方法？

Question

我最近将我的项目从Eclipse迁移到了Android Studio。我试图让电子邮件功能工作，但是遇到了“findViewById”导致的错误。我还收到了由“Toast.makeText”导致的错误。请帮忙解决这两个问题。我的类中的代码如下：

package com.example.ishonours.witsbusapp;

import android.app.Activity;
import android.net.Uri;
import android.os.Bundle;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import android.content.Intent;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class ComplaintsFragment extends Fragment {

//I added
private EditText recipient;
private EditText subject;
private EditText body;


private OnFragmentInteractionListener mListener;
private static final String ARG_SECTION_NUMBER = "5";

public static ComplaintsFragment newInstance(int menuNumber) {
    ComplaintsFragment fragment = new ComplaintsFragment();
    Bundle args = new Bundle();
    args.putInt(ARG_SECTION_NUMBER, menuNumber);
    fragment.setArguments(args);
    return fragment;
}

public ComplaintsFragment() {
    // Required empty public constructor
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return  inflater.inflate(R.layout.fragment_complaints, container, false);

    //i added
    recipient = (EditText) findViewById(R.id.recipient);
    subject = (EditText) findViewById(R.id.subject);
    body = (EditText) findViewById(R.id.body);
    Button sendBtn = (Button) findViewById(R.id.sendEmail);
    sendBtn.setOnClickListener(new View.OnClickListener() {

        public void onClick(View view) {
            sendEmail();
            // after sending the email, clear the fields
            recipient.setText("");
            subject.setText("");
            body.setText("");
        }
    });


}

//i added
protected void sendEmail() {
    String[] recipients = {recipient.getText().toString()};
    Intent email = new Intent(Intent.ACTION_SEND, Uri.parse("mailto:"));
    // prompts email clients only
    email.setType("message/rfc822");
    email.putExtra(Intent.EXTRA_EMAIL, recipients);
    email.putExtra(Intent.EXTRA_SUBJECT, subject.getText().toString());
    email.putExtra(Intent.EXTRA_TEXT, body.getText().toString());
    try {
        // the user can choose the email client
        startActivity(Intent.createChooser(email, "Choose an email client from..."));
    } catch (android.content.ActivityNotFoundException ex) {
        Toast.makeText(ComplaintsFragment.this, "No email client installed.",
               Toast.LENGTH_LONG).show();
    }}




public void onButtonPressed(Uri uri) {
    if (mListener != null) {
        mListener.onFragmentInteraction(uri);
    }
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    ((MainActivity) activity).onSectionAttached(
            getArguments().getInt(ARG_SECTION_NUMBER));
}


@Override
public void onDetach() {
    super.onDetach();
    mListener = null;
}

public interface OnFragmentInteractionListener {
    // TODO: Update argument type and name
    public void onFragmentInteraction(Uri uri);
}

我的 XML 文件中的代码如下：

<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="com.example.ishonours.witsbusapp.ComplaintsFragment">

<TextView
    android:id="@+id/text1"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_marginBottom="20dp"
    android:gravity="center"
    android:text="Complete the fields to log a complaint"
    android:textAppearance="?android:attr/textAppearanceMedium" />

<EditText
    android:id="@+id/recipient"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:inputType="textEmailAddress"
    android:hint="Recipient" />
<EditText
    android:id="@+id/subject"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:hint="Subject" />
<EditText
    android:id="@+id/body"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:hint="Message body" />
<Button
    android:id="@+id/sendEmail"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="30dp"
    android:text="Compose an email" />

- Yusuf

---

可能是Fragment中的findViewById重复问题。 - Sufian

Answer 1

问题出在你的onCreateView方法中。

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
     // Inflate the layout for this fragment
     View v = inflater.inflate(R.layout.fragment_complaints, container, false);

     //i added
     recipient = (EditText) v.findViewById(R.id.recipient);

     [...]

     return v;
}

看到区别了吗？在处理Fragments时，您必须在实际的View对象上调用findViewById。

而您遇到的Toast问题是因为您将错误的对象作为第一个参数传递。您需要Context，但您传递了Fragment。虽然Fragment不是Context，但幸运的是Activity是Context，您必须像这样构造您的Toast：

Toast.makeText(ComplaintsFragment.this.getActivity(), "No email client installed.",
           Toast.LENGTH_LONG).show();

请注意getActivity()的调用。

- pelotasplus

---

我确实看到了区别。非常感谢大家！有没有想法为什么 "Toast.makeText" 没有起作用？ - Yusuf

你收到了什么错误信息？如果你喜欢这些答案，请点赞。 - pelotasplus

好的，我会做。无法解决方法'makeText(theprojectname.CompalintsFragment, .lang.String, int)'。 - Yusuf

只翻译文本内容：有关编程的内容，翻译成中文。感谢您的帮助。 - Yusuf

Answer 2

因此，你的onCreateView方法应该像这样：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.fragment_complaints, container, false);
recipient = (EditText) rootView.findViewById(R.id.recipient);
subject = (EditText) rootView.findViewById(R.id.subject);
body = (EditText) rootView.findViewById(R.id.body);
Button sendBtn = (Button) rootView.findViewById(R.id.sendEmail);
sendBtn.setOnClickListener(new View.OnClickListener() {

    public void onClick(View view) {
        sendEmail();
        // after sending the email, clear the fields
        recipient.setText("");
        subject.setText("");
        body.setText("");
    }
});
return rootView;
}

- Andre Classen