关于BottomNavigationView的使用姿势都在这里了

2023-10-28

一，基本用法

1，首先需要添加依赖：

implementation 'com.google.android.material:material:1.1.0'

2，布局文件中引入：

<com.google.android.material.bottomnavigation.BottomNavigationView
    android:id="@+id/nav_view"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginStart="0dp"
    android:layout_marginEnd="0dp"
    android:background="?android:attr/windowBackground"
    app:menu="@menu/bottom_nav_menu" />

3，常用属性：

app:itemTextColor 文字的颜色，可以通过selector来控制选中和未选中的颜色
app:itemIconTint 图标的颜色，可以通过selector来控制选中和未选中的颜色
app:itemIconSize 图标大小，默认24dp
app:iteamBackground 背景颜色，默认是主题的颜色
app:itemRippleColor 点击后的水波纹颜色
app:itemTextAppearanceActive 设置选中时文字样式
app:itemTextAppearanceInactive 设置默认的文字样式
app:itemHorizontalTranslationEnabled 在label visibility 模式为selected时item水平方向移动
app:elevation 控制控件顶部的阴影
app:labelVisibilityMode 文字的显示模式
app:menu 指定菜单xml文件（文字和图片都写在这个里面）

4，menu文件：

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/navigation_item1"
        android:icon="@drawable/ic_home_black_24dp"
        android:title="@string/title_size" />
    <item
        android:id="@+id/navigation_item2"
        android:icon="@drawable/ic_dashboard_black_24dp"
        android:title="@string/title_style" />
    <item
        android:id="@+id/navigation_item3"
        android:icon="@drawable/ic_notifications_black_24dp"
        android:title="@string/title_in_list" />
</menu>

在每个item中设置对应的icon和title即可。这里的icon可以是一个drawable，也可以是包含不同状态对应不同图片的selector。

设置了menu后一个基本的底部菜单栏就有了。
在这里插入图片描述

5，常用事件

主要用两个事件OnNavigationItemSelectedListener和OnNavigationItemReselectedListener

nav_view.setOnNavigationItemSelectedListener(
    BottomNavigationView.OnNavigationItemSelectedListener {
    when (it.itemId) {
        R.id.navigation_item1 -> {
            Log.e("bottomMenuView:", "home")
            return@OnNavigationItemSelectedListener true
        }
        R.id.navigation_item2 -> {
            Log.e("bottomMenuView:", "dashboard")
            return@OnNavigationItemSelectedListener true
        }
        R.id.navigation_item3 -> {
            Log.e("bottomMenuView:", "notification")
            return@OnNavigationItemSelectedListener true
        }
    }
    false
})

nav_view.setOnNavigationItemReselectedListener(
    BottomNavigationView.OnNavigationItemReselectedListener {
    Log.e("bottomMenuView:", it.itemId.toString())
})

两个事件的用法是一样的，区别在于：OnNavigationItemSelectedListener在item由未选中到选中状态时触发，而OnNavigationItemReselectedListener在item处于选中状态再次点击时触发。

6，最大Item数量

BottomNavigationView对显示的item数量做了显示，最多5个，超过就会抛出异常，源码如下：

public final class BottomNavigationMenu extends MenuBuilder {
  	public static final int MAX_ITEM_COUNT = 5;
	// ...
  	@Override
  	protected MenuItem addInternal(int group, int id, int categoryOrder, CharSequence title) {
    if (size() + 1 > MAX_ITEM_COUNT) {
      throw new IllegalArgumentException(
          "Maximum number of items supported by BottomNavigationView is "
              + MAX_ITEM_COUNT
              + ". Limit can be checked with BottomNavigationView#getMaxItemCount()");
    }
    // ...
    return item;
  }
}

google这么做的原因大概是一般不会有超过5个的需求，而且超过5个以后就会显得很拥挤，UI效果比较差。

二，配合fragment

单纯使用BottomNavigationView并没有什么卵用，一般都是配合fragment来使用。配合fragment使用时有三种方式：

1，FrameLayout + FragmentTransaction

比较古老的一种方式通过getSupportFragmentManager().beginTransaction()获取到FragmentTransaction，然后通过FragmentTransaction的add，show，hide等方法来控制fragment的显示，这种方式比较繁琐就不赘述了。

2，ViewPager

ViewPager一种比较流行的方式，当然你也可以用ViewPager2，用法差不多。需要在布局文件中添加ViewPager。

2.1，设置ViewPager的adapter，如下：

mFragments.add(Fragment1.newInstance())
mFragments.add(Fragment2.newInstance())
mFragments.add(Fragment3.newInstance())
val adapter = object :
    FragmentStatePagerAdapter(
        supportFragmentManager,
        BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT
    ) {
    override fun getItem(position: Int): Fragment {
        return mFragments[position]
    }
<span class="token keyword">override</span> <span class="token keyword">fun</span> <span class="token function">getCount</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">:</span> Int <span class="token punctuation">{<!-- --></span>
    <span class="token keyword">return</span> mFragments<span class="token punctuation">.</span>size
<span class="token punctuation">}</span>

}

viewPager.adapter = adapter

然后需要将ViewPager和BottomNavigationView绑定。

2.2，ViewPager绑定BottomNavigationView

就是在ViewPager切换时更改BottomNavigationView选中项

// 添加viewpager切换监听
viewPager.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
    // ...
    override fun onPageSelected(position: Int) {
        when (position) {
            0 -> {
                navigation.selectedItemId = R.id.navigation_item1
            }
            1 -> {
                navigation.selectedItemId = R.id.navigation_item2
            }
            2 -> {
                navigation.selectedItemId = R.id.navigation_item3
            }
        }
    }
})

2.3，BottomNavigationView绑定ViewPager

同样的，需要在BottomNavigationView选中项改变时更改ViewPager：

navigation.setOnNavigationItemSelectedListener(
    BottomNavigationView.OnNavigationItemSelectedListener { item ->
                when (item.itemId) {
                    R.id.navigation_item1 -> {
                        viewPager.currentItem = 0
                        return@OnNavigationItemSelectedListener true
                    }
                    R.id.navigation_item2 -> {
                        viewPager.currentItem = 1
                        return@OnNavigationItemSelectedListener true
                    }
                    R.id.navigation_item3 -> {
                        viewPager.currentItem = 2
                        return@OnNavigationItemSelectedListener true
                    }
                }
                false
            })

3，配合navigation

这种方式是Google官方目前主推的方式，需要你对navigation有所了解。

1，布局文件如下：

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>com.google.android.material.bottomnavigation.BottomNavigationView</span>
    <span class="token attr-name"><span class="token namespace">android:</span>id</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@+id/nav_view<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>layout_width</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>0dp<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>layout_height</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>wrap_content<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>layout_marginStart</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>0dp<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>layout_marginEnd</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>0dp<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>background</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>?android:attr/windowBackground<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>layout_constraintBottom_toBottomOf</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>layout_constraintLeft_toLeftOf</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>layout_constraintRight_toRightOf</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>menu</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@menu/bottom_nav_menu<span class="token punctuation">"</span></span> <span class="token punctuation">/&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>fragment</span>
    <span class="token attr-name"><span class="token namespace">android:</span>id</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@+id/nav_host_fragment<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>name</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>androidx.navigation.fragment.NavHostFragment<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>layout_width</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>match_parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>layout_height</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>match_parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>defaultNavHost</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>true<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>layout_constraintBottom_toTopOf</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@id/nav_view<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>layout_constraintLeft_toLeftOf</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>layout_constraintRight_toRightOf</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>layout_constraintTop_toTopOf</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">app:</span>navGraph</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@navigation/mobile_navigation<span class="token punctuation">"</span></span> <span class="token punctuation">/&gt;</span></span>

</androidx.constraintlayout.widget.ConstraintLayout>

2，navigation文件

<navigation 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/mobile_navigation"
    app:startDestination="@+id/navigation_home">
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>fragment</span>
    <span class="token attr-name"><span class="token namespace">android:</span>id</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@+id/navigation_item1<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>name</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>per.wsj.bottommenu.ui.fragment.Fragment1<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>label</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@string/title_home<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">tools:</span>layout</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@layout/fragment_home<span class="token punctuation">"</span></span> <span class="token punctuation">/&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>fragment</span>
    <span class="token attr-name"><span class="token namespace">android:</span>id</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@+id/navigation_item2<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>name</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>per.wsj.bottommenu.ui.fragment.Fragment2<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>label</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@string/title_dashboard<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">tools:</span>layout</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@layout/fragment_dashboard<span class="token punctuation">"</span></span> <span class="token punctuation">/&gt;</span></span>

<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>fragment</span>
    <span class="token attr-name"><span class="token namespace">android:</span>id</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@+id/navigation_item2<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>name</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>per.wsj.bottommenu.ui.fragment.Fragment3<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">android:</span>label</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@string/title_notifications<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">tools:</span>layout</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>@layout/fragment_notifications<span class="token punctuation">"</span></span> <span class="token punctuation">/&gt;</span></span>

</navigation>

在navigation中指定了对应的fragment

3，Activity中

接下来的使用就很简单了，调用Activity的扩展函数findNavController，根据布局文件中的fragment标签的id获取NavController，将NavController和BottomNavigationView绑定即可，如下：

val navView: BottomNavigationView = findViewById(R.id.nav_view)
val navController = findNavController(R.id.nav_host_fragment)
navView.setupWithNavController(navController)

效果如下：
在这里插入图片描述

三，显示badge(角标/悬浮徽章)

还在github上查找怎么往BottomNavigationView上添加badge吗？BottomNavigationView默认提供了badge。

1，基本使用

在BottomNavigationView上添加badge很简单，它提供了如下操作badge的方法：

getBadge(int menuItemId) 获取badge
getOrCreateBadge(int menuItemId) 获取或创建badge
removeBadge(int menuItemId) 移除badge

因此添加一个badge只需要如下代码：

val navView: BottomNavigationView = findViewById(R.id.nav_view)
val badge = navView.getOrCreateBadge(R.id.navigation_dashboard)

效果如下：
在这里插入图片描述

纳尼？怎么只有一个红点，胸弟别鸡动，还没设置数量

badge.number = 20

添加数量后效果如下：
在这里插入图片描述

2，常用属性

getBadge和getOrCreateBadge方法返回的都是BadgeDrawable，BadgeDrawable常用的属性/方法如下：

backgroundColor 设置背景色
badgeGravity 设置Badge的显示位置，有四种可先：TOP_START，TOP_END，BOTTOM_START，BOTTOM_END，分别对应左上角，右上角，左下角和右下角。
badgeTextColor 设置文字颜色
maxCharacterCount 最多显示几位数字，比如该项设置了3，number设置为108，则显示99+，如下图所示：

3，注意事项

需要你Application的Theme继承自Theme.MaterialComponents，如下所示：

<style name="AppTheme" parent="Theme.MaterialComponents.Light.DarkActionBar">
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
</style>

4，扩展

同样是位于com.google.android.material包中的TabLayout也可以用同样的方式添加badge

    tabLayout.getTabAt(0).orCreateBadge.apply {
        number = 10
        backgroundColor = Color.RED
    }

四，常用需求

1，动态显示/隐藏MenuItem

有些时候需要根据条件来控制menuItem是否显示，有两种方式可以实现：

1.1， remove

val navView: BottomNavigationView = findViewById(R.id.nav_view)
navView.menu.removeItem(R.id.navigation_spacing)

这种方式是直接把这个item删除掉了，是一个不可逆的过程，也就是说删除后没法再显示出来

1.2， setVisible

// 显示
nav_view.menu.findItem(R.id.navigation_test).isVisible = true
// 隐藏
nav_view.menu.findItem(R.id.navigation_test).isVisible = false

效果如下：
在这里插入图片描述

2，更改字体颜色

创建selector：

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:color="#ff0000" android:state_checked="true"/>
    <item android:color="#00CC00" android:state_checked="false"/>
</selector>

设置app:itemTextColor属性：

<com.google.android.material.bottomnavigation.BottomNavigationView
    android:id="@+id/nav_view"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:background="?android:attr/windowBackground"
    app:itemTextColor="@drawable/selector_menu_text_color"
    app:menu="@menu/bottom_nav_menu" />

效果如下：
在这里插入图片描述

3，修改字体大小

字体大小分为选中的大小和未选中的大小，他们的默认值分别是14sp/12sp，可以通过覆盖原来的字体大小来改变字体大小。

<!--默认字体大小 -->
<dimen name="design_bottom_navigation_text_size">14sp</dimen>
<!--选中字体大小 -->
<dimen name="design_bottom_navigation_active_text_size">14sp</dimen>

修改前后的效果：
在这里插入图片描述

4，自定义选中图标颜色

图标的颜色是通过着色实现的，如果我们的图标不是纯色就需要特殊处理了。

比如如下图标：
在这里插入图片描述

可以通过selector来定义选中和未选中的状态，并设置给menu item的icon

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/ic_custom_icon" android:state_checked="true"/>
    <item android:drawable="@drawable/ic_custom_icon_default" android:state_checked="false"/>
</selector>

然后在activity中设置itemIconTintList为null

nav_view.itemIconTintList = null

效果如下：
在这里插入图片描述

5，labelVisibilityMode

在前面基本属性中已经提到，文字的显示模式有四种:

auto

这种模式就是item数量在三个及以下全部显示label，三个以上只显示选中item的label，效果如下：
selected

该模式下，不管item数量是多少都只显示选中的item的label
labeled

该模式下，不管item数量是多少item的label都显示
unlabeled

该模式下，item的label始终不显示

label的显示模式可以在布局文件中通过labelVisibilityMode设置，也可以在java代码中通过setLabelVisibilityMode设置

6，切换时的动画效果？

很多人说切换时会有动画效果，如下：
在这里插入图片描述

其实这并不是什么动画效果，只是因为选中时文字的字体变大了(实际上是两个字体大小不一样的TextView切换显示状态)，把图标撑起来了，再加上点击时的Ripple效果，感觉就是一个高大上的动效。要去掉这个效果只需要将字体选中和默认的大小改成一致即可，效果如下：
在这里插入图片描述

7，图标文字间距

7.1 调整图标到顶部的距离

如果想调整图标和文字间的距离，改怎么办呢？查了一些资料大部分都是通过添加dimen覆盖默认的design_bottom_navigation_margin来实现。

<dimen name="design_bottom_navigation_margin">4dp</dimen>

该值默认是把8dp，把它调小了，发现图标和文字的距离变大了，这是怎么回事？其实这个距离并不是图标和文字的间距，而是图标距离顶部和底部的Margin值，调小后到顶部的距离也变小了，就显得图标和文字的距离变大了。

如果你有显示badge的需求，那这种方式就出问题了，因为badge是依附于图标的，图标上移，badge也会跟着上移，可以就显示不全了
在这里插入图片描述

7.2 调整文字到底部的距离

那么如果我想调整文字到底部的距离呢？这就需要了解一下每个Item的布局文件design_bottom_navigation_item.xml，其源代码（部分代码省略）如下：

<merge xmlns:android="http://schemas.android.com/apk/res/android">
  <ImageView
      android:id="@+id/icon"
      android:layout_width="24dp"
      android:layout_height="24dp"
      android:layout_marginTop="@dimen/design_bottom_navigation_margin"
      android:layout_marginBottom="@dimen/design_bottom_navigation_margin"
      android:layout_gravity="center_horizontal"/>
  <com.google.android.material.internal.BaselineLayout
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="bottom|center_horizontal"
      android:paddingBottom="10dp">
    <TextView
        android:id="@+id/smallLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="@dimen/design_bottom_navigation_text_size"/>
    <TextView
        android:id="@+id/largeLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="@dimen/design_bottom_navigation_active_text_size"
        android:visibility="invisible"/>
  </com.google.android.material.internal.BaselineLayout>
</merge>

可见如果想修改文字到底部的距离可以改动其父容器BaselineLayout的bottomMargin属性，或调用父容器的scrollBy()使内部的TextView向下偏移，当然此时就需要用到反射。

public static void hookBnv(BottomNavigationView menu) throws Exception{
    Class<BottomNavigationView> bottomNavigationViewClass = BottomNavigationView.class;
    Field menuViewField = bottomNavigationViewClass.getDeclaredField("menuView");
    menuViewField.setAccessible(true);
    Object menuView = menuViewField.get(menu);
Class<span class="token generics function"><span class="token punctuation">&lt;</span>BottomNavigationMenuView<span class="token punctuation">&gt;</span></span> bottomNavigationMenuViewClass <span class="token operator">=</span> BottomNavigationMenuView<span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">;</span>
Field buttonsField <span class="token operator">=</span> bottomNavigationMenuViewClass<span class="token punctuation">.</span><span class="token function">getDeclaredField</span><span class="token punctuation">(</span><span class="token string">"buttons"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
buttonsField<span class="token punctuation">.</span><span class="token function">setAccessible</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Object<span class="token punctuation">[</span><span class="token punctuation">]</span> buttons <span class="token operator">=</span> <span class="token punctuation">(</span>Object<span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">)</span> buttonsField<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>menuView<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">for</span> <span class="token punctuation">(</span>Object button <span class="token operator">:</span> buttons<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    Class<span class="token generics function"><span class="token punctuation">&lt;</span>BottomNavigationItemView<span class="token punctuation">&gt;</span></span> bottomNavigationItemViewClass <span class="token operator">=</span> BottomNavigationItemView<span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">;</span>
    Field smallLabelField <span class="token operator">=</span> bottomNavigationItemViewClass<span class="token punctuation">.</span><span class="token function">getDeclaredField</span><span class="token punctuation">(</span><span class="token string">"smallLabel"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    smallLabelField<span class="token punctuation">.</span><span class="token function">setAccessible</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    TextView smallLabel <span class="token operator">=</span> <span class="token punctuation">(</span>TextView<span class="token punctuation">)</span> smallLabelField<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>button<span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token comment">// 方式一:</span>

// ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) ((ViewGroup) smallLabel.getParent()).getLayoutParams();
// layoutParams.bottomMargin = -15;
// ((ViewGroup) smallLabel.getParent()).setLayoutParams(layoutParams);
// 方式二:
((ViewGroup) smallLabel.getParent()).scrollBy(0,-15);
}
}

效果如下：
在这里插入图片描述

8，修改控件高度

BottomNavigationView的默认高度是56dp，如果遇到操蛋的需求非要改它的话就覆盖一下design_bottom_navigation_height吧，如下：

<dimen name="design_bottom_navigation_height">84dp</dimen>

四，结语

关于BottomNavigationView可能用到的知识点就这些了，如果你还有还有什么奇葩的需求，那就去**“look the fuck resource code”** 吧

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Android