前言

1.老规矩先来看看京东tab栏的效果

jingdong.gif

2.demo实现的效果

demo效果.gif

此功能核心是Lottie库，对Lottie不熟悉的朋友们可以先了解下或者参考
1.Lottie github
2.Lottie- 让Android动画实现更简单
……

实现

1.build.gradle依赖

implementation 'com.airbnb.android:lottie:3.7.0'
implementation 'com.google.android.material:material:1.2.1'
implementation 'androidx.core:core-ktx:1.0.2'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'

2.activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 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"
    tools:context=".MainActivity">
    <FrameLayout
        android:id="@+id/rlMainContainer"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginBottom="50dp"
        android:background="@android:color/white"
        tools:ignore="MissingConstraints" />
    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bnvMain"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:layout_gravity="bottom"
        app:itemRippleColor="@null"
        android:background="@android:color/white"
        app:labelVisibilityMode="labeled"
        app:itemTextColor="@drawable/selector_main_bottom_text"
        app:menu="@menu/main_menu_bottom_navigation"
        tools:ignore="MissingConstraints" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>

3.selector_main_bottom_text.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:color="@color/color999" android:state_enabled="false" />
    <item android:color="@color/color333" />
</selector>

4.main_menu_bottom_navigation.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <item
        android:id="@+id/home"
        android:title="首页"
        tools:ignore="MenuTitle"/>
    <item
        android:id="@+id/service"
        android:title="服务中心"/>
    <item
        android:id="@+id/application"
        android:title="应用"/>
    <item
        android:id="@+id/mine"
        android:title="我的"/>
</menu>

5.MainActivity

package com.dawnling.dynamictab

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.core.view.forEach
import androidx.fragment.app.Fragment
import com.airbnb.lottie.LottieCompositionFactory
import com.airbnb.lottie.LottieDrawable
import com.google.android.material.bottomnavigation.BottomNavigationItemView
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {
    private lateinit var mFragments: MutableMap<Int, Fragment>
    private var mLottieJsonMap = mutableMapOf(
        R.id.home to "lottie/main_tab_home.json",
        R.id.service to "lottie/main_tab_mine.json",
        R.id.application to "lottie/main_tab_home.json",
        R.id.mine to "lottie/main_tab_mine.json"
    )

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        hideTooltip()
        initFragment()
        val initialItemId = R.id.home
        initShow(initialItemId)
        bnvMain.setOnNavigationItemSelectedListener {
            initShow(it.itemId)
            true
        }
    }

    private fun initFragment() {
        val fragment1 = BlankFragment.newInstance(0)
        val fragment2 = BlankFragment.newInstance(1)
        val fragment3 = BlankFragment.newInstance(2)
        val fragment4 = BlankFragment.newInstance(3)
        mFragments = mutableMapOf(
            R.id.home to fragment1,
            R.id.service to fragment2,
            R.id.application to fragment3,
            R.id.mine to fragment4
        )
    }

    private fun initShow(itemId: Int){
        showFragment(itemId)
        setLottieDrawable(mLottieJsonMap, itemId)
    }

    private fun showFragment(menuItemId: Int){
        var curFragment = supportFragmentManager.fragments.find {
            it.isVisible && it in mFragments.values
        }
        var targetFragment = mFragments[menuItemId]
        supportFragmentManager.beginTransaction().apply {
            curFragment?.let { if (it.isVisible) hide(it) }
            targetFragment?.let {
                if (it.isAdded) show(it) else add(R.id.rlMainContainer, it)
            }
        }.commit()
    }

    /* 隐藏长按 BottomNavigationItemView 会出现 Toast 的问题*/
    private fun hideTooltip() {
        bnvMain.menu.forEach {
            val menuItemView = findViewById<BottomNavigationItemView>(it.itemId)
            menuItemView.setOnLongClickListener {
                true
            }
        }
    }

    /*设置 LottieDrawable 到每个 MenuItem,并且设置播放动画*/
    private fun setLottieDrawable(lottieJsonMap: MutableMap<Int, String>, itemId: Int) {
        bnvMain.menu.forEach {
            it.icon = LottieDrawable().apply {
                var result =
                    LottieCompositionFactory.fromAssetSync(this@MainActivity, lottieJsonMap[it.itemId])
                composition = result.value
            }
            if (it.itemId == itemId) {
                (it.icon as LottieDrawable).playAnimation()
            }
        }
    }
}

其中main_tab_home.json和main_tab_mine.json需要UI提供
demo下载