bottomnavigationview 中间凸起

要在 BottomNavigationView 中间凸起，可以使用第三方库来实现，比如使用 AHBottomNavigation 库。步骤如下：

1. 在 build.gradle 文件中添加依赖：

dependencies {
    implementation 'com.aurelhubert:ahbottomnavigation:2.1.0'
}

2. 在布局文件中添加 AHBottomNavigation 控件：

<com.aurelhubert.ahbottomnavigation.AHBottomNavigation
    android:id="@+id/bottom_navigation"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:ah_bottom_navigation_background_color="@color/colorPrimary"
    app:ah_bottom_navigation_title_text_color="@color/white"
    app:ah_bottom_navigation_active_item_color="@android:color/white"
    app:ah_bottom_navigation_inactive_item_color="@color/white"
    app:ah_bottom_navigation_shadow="false"
    app:ah_bottom_navigation_use_theme_colors="false"
    app:ah_bottom_navigation_default_background_color="@color/colorPrimary"
    app:ah_bottom_navigation_item_margin_top="8dp"
    app:ah_bottom_navigation_selected_item="1"
    app:ah_bottom_navigation_notification_background_color="@color/colorAccent"
    app:ah_bottom_navigation_notification_margin_left="4dp"
    app:ah_bottom_navigation_notification_margin_top="4dp"
    app:ah_bottom_navigation_notification_text_size="10sp" />

3. 在代码中设置 BottomNavigationView：

AHBottomNavigation bottomNavigationView = (AHBottomNavigation) findViewById(R.id.bottom_navigation);

// 添加导航项
AHBottomNavigationItem item1 = new AHBottomNavigationItem(R.string.tab_1, R.drawable.ic_home, R.color.color_tab_1);
AHBottomNavigationItem item2 = new AHBottomNavigationItem(R.string.tab_2, R.drawable.ic_search, R.color.color_tab_2);
AHBottomNavigationItem item3 = new AHBottomNavigationItem(R.string.tab_3, R.drawable.ic_profile, R.color.color_tab_3);
bottomNavigationView.addItem(item1);
bottomNavigationView.addItem(item2);
bottomNavigationView.addItem(item3);

// 设置中间凸起
bottomNavigationView.setBehaviorTranslationEnabled(false);
AHBottomNavigationItem item = new AHBottomNavigationItem("", R.drawable.ic_add, R.color.color_tab_add);
bottomNavigationView.addItem(item);
bottomNavigationView.setTitleState(AHBottomNavigation.TitleState.ALWAYS_SHOW);

注意，AHBottomNavigation 库中的 BottomNavigationView 并非是 Android 原生的 BottomNavigationView，因此在使用时需要注意一些细节。