Don't get discouraged if you miss a lot of the details in converting the code. The authors pretty much throw you into the deep end with this exercise. Be sure to study the solution on pp. 330-331 and make sure you understand why each change is necessary.

The summary of converting Activities to Fragments is:

• Change the class name to {whatever}Fragment and change the parent class to Fragment.
• Make all lifecycle methods public.
• Define an onCreateView method in which you inflate the layout.
• Remove any cruft from the lifecycle methods.
• Be very careful about when/where/how Views are accessed (esp. anything that relies on the parent's layout) and refactor the code as needed.

The last item above is often the most challenging.

StopwatchFragment.java

package com.hfad.workout;
 
import android.os.Bundle;
import android.os.Handler;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
 
public class StopwatchFragment extends Fragment {
    //Number of seconds displayed on the stopwatch.
    private int seconds = 0;
    //Is the stopwatch running?
    private boolean running;
    private boolean wasRunning;
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (savedInstanceState != null) {
            seconds = savedInstanceState.getInt("seconds");
            running = savedInstanceState.getBoolean("running");
            wasRunning = savedInstanceState.getBoolean("wasRunning");
            if (wasRunning) {
                running = true;
            }
        }
    }
 
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View layout = inflater.inflate(R.layout.fragment_stopwatch, container, false);
        runTimer(layout);
        return layout;
    }
 
    @Override
    public void onPause() {
        super.onPause();
        wasRunning = running;
        running = false;
    }
 
    @Override
    public void onResume() {
        super.onResume();
        if (wasRunning) {
            running = true;
        }
    }
 
    @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
        savedInstanceState.putInt("seconds", seconds);
        savedInstanceState.putBoolean("running", running);
        savedInstanceState.putBoolean("wasRunning", wasRunning);
    }
 
    public void onClickStart(View view) {
        running = true;
    }
 
    public void onClickStop(View view) {
        running = false;
    }
 
    public void onClickReset(View view) {
        running = false;
        seconds = 0;
    }
 
    private void runTimer(View view) {
        final TextView timeView = (TextView) view.findViewById(R.id.time_view);
        final Handler handler = new Handler();
        handler.post(new Runnable() {
            @Override
            public void run() {
                int hours = seconds / 3600;
                int minutes = (seconds % 3600) / 60;
                int secs = seconds % 60;
                String time = String.format("%d:%02d:%02d",
                        hours, minutes, secs);
                timeView.setText(time);
                if (running) {
                    seconds++;
                }
                handler.postDelayed(this, 1000);
            }
        });
    }
}

fragment_stopwatch.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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">
 
    <TextView
        android:id="@+id/time_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="0dp"
        android:text=""
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:textSize="92sp" />
 
    <Button
        android:id="@+id/start_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/time_view"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp"
        android:onClick="onClickStart"
        android:text="@string/start" />
 
    <Button
        android:id="@+id/stop_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/start_button"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="10dp"
        android:onClick="onClickStop"
        android:text="@string/stop" />
 
    <Button
        android:id="@+id/reset_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/stop_button"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="10dp"
        android:onClick="onClickReset"
        android:text="@string/reset" />
</RelativeLayout>