实验 用fragment实现底部导航条 界面如下图所示，底部有4个导航图标分别为提醒、消息、收藏和我的，点击底部4分图标，在屏幕主区加载相应的Fragment,界面标题、图标颜色和背景也相应改变。实现滑屏（左右滑动，底部图标跟着移动）功能

好的，这里提供一下实现的思路：

1.创建4个Fragment分别对应4个导航图标，每个Fragment对应一个布局文件。

2.在主界面中添加一个FrameLayout作为Fragment的容器，用于加载Fragment。

3.创建一个底部导航栏布局，在布局中添加4个ImageView作为导航图标。

4.监听底部导航栏的点击事件，根据点击的位置加载对应的Fragment，并改变标题、图标颜色和背景。

5.通过ViewPager和FragmentPagerAdapter实现滑屏功能，底部导航栏随着滑动位置改变。

下面是示例代码：

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private ImageView ivRemind, ivMessage, ivFavorite, ivMine;
    private TextView tvTitle;
    private FrameLayout flContainer;
    private ViewPager viewPager;
    private List<Fragment> fragmentList;
    private int[] iconNormal = {R.drawable.icon_remind_normal, R.drawable.icon_message_normal, R.drawable.icon_favorite_normal, R.drawable.icon_mine_normal};
    private int[] iconSelected = {R.drawable.icon_remind_selected, R.drawable.icon_message_selected, R.drawable.icon_favorite_selected, R.drawable.icon_mine_selected};

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

        initView();
        initData();
        initListener();
    }

    private void initView() {
        ivRemind = findViewById(R.id.iv_remind);
        ivMessage = findViewById(R.id.iv_message);
        ivFavorite = findViewById(R.id.iv_favorite);
        ivMine = findViewById(R.id.iv_mine);
        tvTitle = findViewById(R.id.tv_title);
        flContainer = findViewById(R.id.fl_container);
        viewPager = findViewById(R.id.view_pager);
    }

    private void initData() {
        fragmentList = new ArrayList<>();
        fragmentList.add(new RemindFragment());
        fragmentList.add(new MessageFragment());
        fragmentList.add(new FavoriteFragment());
        fragmentList.add(new MineFragment());

        viewPager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
        viewPager.setOffscreenPageLimit(4);
        viewPager.setCurrentItem(0);

        setSelected(0);
    }

    private void initListener() {
        ivRemind.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                viewPager.setCurrentItem(0);
                setSelected(0);
            }
        });

        ivMessage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                viewPager.setCurrentItem(1);
                setSelected(1);
            }
        });

        ivFavorite.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                viewPager.setCurrentItem(2);
                setSelected(2);
            }
        });

        ivMine.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                viewPager.setCurrentItem(3);
                setSelected(3);
            }
        });

        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                setSelected(position);
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
    }

    private void setSelected(int position) {
        ivRemind.setImageResource(iconNormal[0]);
        ivMessage.setImageResource(iconNormal[1]);
        ivFavorite.setImageResource(iconNormal[2]);
        ivMine.setImageResource(iconNormal[3]);

        switch (position) {
            case 0:
                ivRemind.setImageResource(iconSelected[0]);
                tvTitle.setText("提醒");
                break;
            case 1:
                ivMessage.setImageResource(iconSelected[1]);
                tvTitle.setText("消息");
                break;
            case 2:
                ivFavorite.setImageResource(iconSelected[2]);
                tvTitle.setText("收藏");
                break;
            case 3:
                ivMine.setImageResource(iconSelected[3]);
                tvTitle.setText("我的");
                break;
        }
    }

    private class MyPagerAdapter extends FragmentPagerAdapter {

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

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

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

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <FrameLayout
        android:id="@+id/fl_container"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_above="@+id/bottom_layout"
        android:layout_weight="1" />

    <LinearLayout
        android:id="@+id/bottom_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:background="#FFFFFF"
        android:orientation="horizontal">

        <ImageView
            android:id="@+id/iv_remind"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:src="@drawable/icon_remind_normal" />

        <ImageView
            android:id="@+id/iv_message"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:src="@drawable/icon_message_normal" />

        <ImageView
            android:id="@+id/iv_favorite"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:src="@drawable/icon_favorite_normal" />

        <ImageView
            android:id="@+id/iv_mine"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:src="@drawable/icon_mine_normal" />
    </LinearLayout>

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:layout_above="@+id/bottom_layout"
        android:background="#2196F3"
        android:gravity="center"
        android:text="提醒"
        android:textColor="#FFFFFF"
        android:textSize="20sp" />

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_above="@+id/bottom_layout"
        android:layout_weight="1" />
</RelativeLayout>

RemindFragment.java

public class RemindFragment extends Fragment {

    public RemindFragment() {
    }

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

fragment_remind.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="提醒页面"/>

</LinearLayout>

其他Fragment和布局文件类似，这里就不赘述了。