5장. Fragment

1. SampleFragment

1-1. fragment_main.xml

<?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=".MainFragment" >

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="메인 프래그먼트"
        android:textSize="30sp" />

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

 

1-2. fragment_menu.xml

<?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:background="@android:color/holo_orange_light"
    android:orientation="vertical"
    tools:context=".MainFragment">

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="메뉴 프래그먼트"
        android:textSize="30sp" />

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

 

1-3. MainActivity.java

public class MainActivity extends AppCompatActivity {
    MainFragment mainFragment;
    MenuFragment menuFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mainFragment = (MainFragment) getSupportFragmentManager().findFragmentById(R.id.mainFragment);
        menuFragment = new MenuFragment();
    }

    public void onFragmentChanged(int index) {
        if (index == 0) {
            getSupportFragmentManager().beginTransaction().replace(R.id.container, menuFragment).commit();
        } else if (index == 1) {
            getSupportFragmentManager().beginTransaction().replace(R.id.container, mainFragment).commit();
        }
    }
}

 

1-4. MainFragment.java

public class MainFragment extends Fragment {

    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.fragment_main, container, false);

        Button button = rootView.findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                MainActivity activity = (MainActivity) getContext();
                activity.onFragmentChanged(0);
            }
        });
        return rootView;
    }
}

 

1-5. MenuFragment.java

public class MenuFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.fragment_menu, container, false);

        Button button = rootView.findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                MainActivity activity = (MainActivity) getContext();
                activity.onFragmentChanged(1);
            }
        });
        return rootView;
    }
}

 

---

2. SampleTap

2-1. fragment1.xml (2, 3도 마찬가지)

<?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:background="@android:color/holo_blue_bright"
    android:orientation="vertical"
    tools:context=".Fragment1">

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

 

2-2. activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.coordinatorlayout.widget.CoordinatorLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.google.android.material.appbar.AppBarLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

            <androidx.appcompat.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:background="?colorPrimaryDark"
                android:elevation="1dp"
                android:theme="@style/ThemeOverlay.AppCompat.Dark">

                <TextView
                    android:id="@+id/titleText"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="타이틀"
                    android:textAppearance="@style/Base.TextAppearance.Widget.AppCompat.Toolbar.Title" />

            </androidx.appcompat.widget.Toolbar>

            <com.google.android.material.tabs.TabLayout
                android:id="@+id/tabs"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:background="@android:color/background_light"
                android:elevation="1dp"
                app:tabGravity="fill"
                app:tabMode="fixed"
                app:tabSelectedTextColor="?colorAccent"
                app:tabTextColor="?colorPrimary" />
        </com.google.android.material.appbar.AppBarLayout>

        <FrameLayout
            android:id="@+id/container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">

        </FrameLayout>
    </androidx.coordinatorlayout.widget.CoordinatorLayout>
</RelativeLayout>

 

2-3. Fragment1.java (2, 3도 마찬가지)

public class Fragment1 extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment1, container, false);
    }
}

 

2-4. MainActivity.java

public class MainActivity extends AppCompatActivity {

    Toolbar toolbar;
    Fragment1 fragment1;
    Fragment2 fragment2;
    Fragment3 fragment3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        ActionBar actionBar = getSupportActionBar();
        actionBar.setDisplayShowTitleEnabled(false);

        fragment1 = new Fragment1();
        fragment2 = new Fragment2();
        fragment3 = new Fragment3();

        getSupportFragmentManager().beginTransaction().replace(R.id.container, fragment1).commit();

        TabLayout tabs = findViewById(R.id.tabs);
        tabs.addTab(tabs.newTab().setText("통화기록"));
        tabs.addTab(tabs.newTab().setText("스팸기록"));
        tabs.addTab(tabs.newTab().setText("연락처"));
        tabs.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                int position = tab.getPosition();
                Log.d("MainActivity", "선택된 탭 : " + position);

                Fragment selected = null;
                if (position == 0) {
                    selected = fragment1;
                } else if (position == 1) {
                    selected = fragment2;
                } else if (position == 2) {
                    selected = fragment3;
                }
                getSupportFragmentManager().beginTransaction()
                        .replace(R.id.container, selected).commit();
            }
            @Override
            public void onTabUnselected(TabLayout.Tab tab) {}

            @Override
            public void onTabReselected(TabLayout.Tab tab) {}
        });
    }
}

 

---

3. SamplePager (뷰 페이저)

3-1. fragment1.xml (2, 3도 마찬가지)

<?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:background="@android:color/holo_blue_bright"
    android:orientation="vertical"
    tools:context=".Fragment1">

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

 

3-2. activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="두번째 화면 보여주기" />

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.viewpager.widget.PagerTitleStrip
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="top"
            android:background="#55cedf"
            android:textColor="#FFFFFF"
            android:paddingTop="5dp"
            android:paddingBottom="5dp">
        </androidx.viewpager.widget.PagerTitleStrip>

    </androidx.viewpager.widget.ViewPager>
</LinearLayout>

 

3-3. Fragment1.java

public class Fragment1 extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment1, container, false);
    }
}

 

3-4. MainActivity.java

public class MainActivity extends AppCompatActivity {
    ViewPager pager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        pager = findViewById(R.id.pager);
        pager.setOffscreenPageLimit(3);

        MyPagerAdapter adapter = new MyPagerAdapter(getSupportFragmentManager());

        Fragment1 fragment1 = new Fragment1();
        adapter.addItem(fragment1);

        Fragment2 fragment2 = new Fragment2();
        adapter.addItem(fragment2);

        Fragment3 fragment3 = new Fragment3();
        adapter.addItem(fragment3);

        pager.setAdapter(adapter);

        Button button = findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                pager.setCurrentItem(1);
            }
        });
    }

    class MyPagerAdapter extends FragmentStatePagerAdapter {
        ArrayList<Fragment> items = new ArrayList<Fragment>();

        public MyPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        public void addItem(Fragment item) {
            items.add(item);
        }

        @Override
        public Fragment getItem(int position) {
            return items.get(position);
        }

        @Override
        public int getCount() {
            return items.size();
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return "페이지 " + position;
        }
    }
}

 

 

---

4. NavigationDrawer (SampleDrawer)

4-1. fragment1.xml (2, 3도 마찬가지)

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/holo_blue_bright">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:text="첫번째"
        android:textSize="40dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

 

4-2. nav_header_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="@dimen/nav_header_height"
    android:background="@drawable/side_nav_bar"
    android:gravity="bottom"
    android:orientation="vertical"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:theme="@style/ThemeOverlay.AppCompat.Dark">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentDescription="@string/nav_header_desc"
        android:paddingTop="@dimen/nav_header_vertical_spacing"
        app:srcCompat="@mipmap/ic_launcher_round" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/nav_header_vertical_spacing"
        android:text="@string/nav_header_title"
        android:textAppearance="@style/TextAppearance.AppCompat.Body1" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/nav_header_subtitle" />

</LinearLayout>

 

4-3. activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

    <androidx.coordinatorlayout.widget.CoordinatorLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <com.google.android.material.appbar.AppBarLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:theme="@style/Theme.SampleDrawer.AppBarOverlay">

            <androidx.appcompat.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:background="?attr/colorPrimary"
                app:popupTheme="@style/Theme.SampleDrawer.PopupOverlay" />

        </com.google.android.material.appbar.AppBarLayout>

        <FrameLayout
            android:id="@+id/container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">
        </FrameLayout>

    </androidx.coordinatorlayout.widget.CoordinatorLayout>

    <com.google.android.material.navigation.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header_main"
        app:menu="@menu/activity_main_drawer" />

</androidx.drawerlayout.widget.DrawerLayout>

 

4-4. Fragment1.java

public class Fragment1 extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.fragment1, container, false);

        return rootView;
    }
}

 

 

4-5. FragmentCallback.java

public interface FragmentCallback {

    public void onFragmentSelected(int position, Bundle bundle);
}

 

4-6. MainActivity.java

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener, FragmentCallback {

    Fragment1 fragment1;
    Fragment2 fragment2;
    Fragment3 fragment3;

    DrawerLayout drawer;
    Toolbar toolbar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        drawer = findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        fragment1 = new Fragment1();
        fragment2 = new Fragment2();
        fragment3 = new Fragment3();

        getSupportFragmentManager().beginTransaction().add(R.id.container, fragment1).commit();
    }

    @Override
    public void onBackPressed() {
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.menu1) {
            Toast.makeText(this, "첫번째 메뉴 선택됨.", Toast.LENGTH_LONG).show();
            onFragmentSelected(0, null);
        } else if (id == R.id.menu2) {
            Toast.makeText(this, "두번째 메뉴 선택됨.", Toast.LENGTH_LONG).show();
            onFragmentSelected(1, null);
        } else if (id == R.id.menu3) {
            Toast.makeText(this, "세번째 메뉴 선택됨.", Toast.LENGTH_LONG).show();
            onFragmentSelected(2, null);
        }

        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    @Override
    public void onFragmentSelected(int position, Bundle bundle) {
        Fragment curFragment = null;

        if (position == 0) {
            curFragment = fragment1;
            toolbar.setTitle("첫번째 화면");
        } else if (position == 1) {
            curFragment = fragment2;
            toolbar.setTitle("두번째 화면");
        } else if (position == 2) {
            curFragment = fragment3;
            toolbar.setTitle("세번째 화면");
        }
        getSupportFragmentManager().beginTransaction().replace(R.id.container, curFragment).commit();
    }
}

 

 

---

5. [LAB] Fragment들을 사용하여 이미지 변환

5-1. fragment_viewer.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    
    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:srcCompat="@drawable/dream01" />
</LinearLayout>

 

5-2. fragment_list.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="첫 번째 이미지" />

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="두 번째 이미지" />

    <Button
        android:id="@+id/button3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="세 번째 이미지" />
</LinearLayout>

 

5-3. activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <fragment
        android:id="@+id/listFragment"
        android:name="com.example.myapplication.ListFragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />

    <fragment
        android:id="@+id/viewerFragment"
        android:name="com.example.myapplication.ViewerFragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />
</LinearLayout>

 

5-4. ListFragment.java

// Fragment 클래스를 상속한 ListFragment 생성
public class ListFragment extends Fragment {

    // MainActivity.java에서 사용할 인터페이스, 콜백에 사용할 것임
    public static interface ImageSelectionCallback {
        public void onImageSelected(int position);
    }

    // 콜백 인스턴스 담을 변수 생성
    public ImageSelectionCallback callback;

    // Fragment 클래스의 onAttach 메소드 오버라이딩 : 콜백 인스턴스에 context를 지정하여 액티비티 참조(이곳의 context는 얘를 호출하는 녀석, 즉 MainActivity가 될 것임)
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);

        if (context instanceof ImageSelectionCallback) {
            callback = (ImageSelectionCallback) context;
        }
    }

    // Fragment 클래스의 onCreateView 메소드 오버라이딩 : 해당 뷰 내부요소 구성은 여기서 지정 (MainActivity의 onCreate()와 유사)
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        // 레이아웃을 화면 일부에 표시해주는 LayoutInflater를 포함하여 뷰그룹 지정
        ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.fragment_list, container, false);
        
        // 3개의 버튼 클릭 시의 동작 : 콜백 함수를 통해 onImageSelected(num) 전달
        // 버튼 지정 시에 뷰그룹 내에서 찾아야 함, 따라서 rootView.findViewById(...) 로 지정
        // 버튼 기능 구현 : callback이 존재한다면(즉 not null), callback에게 어떠한 함수를 요청한다.
        // Hint : callback 의 타입은 ImageSelectionCallback 이다. 해당 인터페이스의 선언문으로 가보자.
        // Hint 2 : 이 파일 상단에 있다.
        Button button = rootView.findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (callback != null) {
                    callback.onImageSelected(1);
                }
            }
        });

        Button button2 = rootView.findViewById(R.id.button2);
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (callback != null) {
                    callback.onImageSelected(2);
                }
            }
        });

        Button button3 = rootView.findViewById(R.id.button3);
        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (callback != null) {
                    callback.onImageSelected(3);
                }
            }
        });
        return rootView;
    }
}

 

5-5. ViewerFragment.java

// 이미지를 표시해주는 Fragment
public class ViewerFragment extends Fragment {
    ImageView imageView;

    // 뷰가 생성될 때의 동작(MainActivity의 onCreate()와 유사)
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.fragment_viewer, container, false);
        imageView = rootView.findViewById(R.id.imageView);

        return rootView;
    }
    
    // 이미지 세팅해주는 알맹이 함수
    public void setImage(int resId) {
        imageView.setImageResource(resId);
    }
}

 

5-6. MainActivity.java

// MainActivity는 ListFragment.ImageSelectionCallback 인터페이스를 implement한다.
public class MainActivity extends AppCompatActivity implements ListFragment.ImageSelectionCallback {
    // 리스트 Fragment 담는 변수
    ListFragment listFragment;
    
    // 이미지 Fragment 담는 변수
    ViewerFragment viewerFragment;
    
    // MainActivity에서 image들을 받아다가 여기서 인자로 넘길 때 사용
    int[] images = {R.drawable.dream01, R.drawable.dream02, R.drawable.dream03};
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        // FragmentManager 변수를 통해 Fragment 관리
        FragmentManager manager = getSupportFragmentManager();
        // id를 집어넣어서 변수에 인스턴스를 추가합시다
        listFragment = (ListFragment) manager.findFragmentById(R.id.listFragment);
        viewerFragment = (ViewerFragment) manager.findFragmentById(R.id.viewerFragment);
    }

    // ListFragment.ImageSelectionCallback 인터페이스 implement에 의해 선언된 오버라이드 메소드
    // Hint : ListFragment.java 파일에서 버튼 동작을 작성했다면, 여기서 그 구체적인 행동을 지정하는 것
    // Hint 2 : 어느 이미지를 고를지를 ListFragment에서 position 인자로 넘겼으니, 그걸 설정하는 Fragment는 누굴까? 그녀석의 메소드를 불러올 필요가 있을 것이다.
    @Override
    public void onImageSelected(int position) {
        if (position == 1) {
            viewerFragment.setImage(images[0]);
        } else if (position == 2) {
            viewerFragment.setImage(images[1]);
        } else if (position == 3) {
            viewerFragment.setImage(images[2]);
        }
    }
}