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创建一个包含“首页”、“分类”和“我的”选项卡的TabBar并实现切换功能，通常可以通过使用TabLayout结合ViewPager或ViewPager2来完成。以下是一个基本的示例，展示了如何使用Kotlin和XML来实现这个功能。
1.添加依赖项到build.gradle
dependencies {// ...implementation("com.google.android.material:material:1.8.0")implementation("androidx.viewpager2:viewpager2:1.0.0")
}2.在你的布局XML文件中定义TabLayout和ViewPager2
<?xml version="1.0" encoding="utf-8"?>
<LinearLayoutxmlns: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:orientation="vertical"><androidx.viewpager2.widget.ViewPager2android:id="@+id/viewPager"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1" /><com.google.android.material.tabs.TabLayoutandroid:id="@+id/tabLayout"android:layout_width="match_parent"android:layout_height="wrap_content"app:tabMode="fixed"app:tabGravity="fill"app:tabIndicatorHeight="0dp" /></LinearLayout>3.在你的Activity中设置ViewPager2和TabLayout
package com.example.gatestdemol.tabbarimport androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import androidx.viewpager2.adapter.FragmentStateAdapter
import com.example.gatestdemol.databinding.ActivityTabBarBinding
import com.google.android.material.tabs.TabLayoutMediatorclass TabBarActivity : AppCompatActivity() {private lateinit var binding: ActivityTabBarBindingoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)// setContentView(R.layout.activity_tab_bar)binding = ActivityTabBarBinding.inflate(layoutInflater)setContentView(binding.root)val adapter = ViewPagerAdapter(this)binding.viewPager.adapter = adapterTabLayoutMediator(binding.tabLayout, binding.viewPager) { tab, position ->tab.text = when(position) {0 -> "首页"1 -> "分类"2 -> "我的"else -> null}}.attach()}private inner class ViewPagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {override fun getItemCount(): Int {return 3}override fun createFragment(position: Int): Fragment {return when(position) {0 -> HomeFragment()1 -> CategoryFragment()2 -> ProfileFragment()else -> Fragment()}}}}在上面的代码中，我们创建了一个ViewPagerAdapter类继承自FragmentStateAdapter，并重写了getItemCount和createFragment方法来分别返回选项卡的数量和对应的Fragment。TabLayoutMediator用于将TabLayout和ViewPager2绑定起来，并设置每个选项卡的标题。
4.创建对应的Fragment类
package com.example.gatestdemol.tabbarimport android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import com.example.gatestdemol.databinding.FragmentHomeBindingclass HomeFragment: Fragment() {private var binding: FragmentHomeBinding? = nulloverride fun onCreateView(inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?): View? {binding = FragmentHomeBinding.inflate(inflater,container,false)return binding?.root}override fun onDestroy() {super.onDestroy()binding = null}}class CategoryFragment : Fragment() {// 实现分类Fragment的布局和逻辑
}class ProfileFragment : Fragment() {// 实现我的Fragment的布局和逻辑
}每个Fragment对应一个页面，在这里你可以实现各自的布局和业务逻辑。
这是一个基本的TabBar实现，你可以根据自己的需求添加图标、自定义样式等。
简单TabBar示意图:
5.TabBar添加Icon
package com.example.gatestdemol.tabbarimport androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.core.content.ContextCompat
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import androidx.viewpager2.adapter.FragmentStateAdapter
import com.example.gatestdemol.R
import com.example.gatestdemol.databinding.ActivityTabBarBinding
import com.google.android.material.tabs.TabLayout
import com.google.android.material.tabs.TabLayoutMediatorclass TabBarActivity : AppCompatActivity() {private lateinit var binding: ActivityTabBarBindingoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)binding = ActivityTabBarBinding.inflate(layoutInflater)setContentView(binding.root)val adapter = ViewPagerAdapter(this)binding.viewPager.adapter = adapterTabLayoutMediator(binding.tabLayout, binding.viewPager) { tab, position ->tab.text = when(position) {0 -> "首页"1 -> "分类"2 -> "我的"else -> null}tab.icon = when(position) {0 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_home_default)1 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_category_default)2 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_profile_default)else -> null}}.attach()binding.tabLayout.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {override fun onTabSelected(tab: TabLayout.Tab?) {// 一套Icon时用这种方式//tab?.icon?.setTint(ContextCompat.getColor(applicationContext, R.color.your_selected_text_color))// 两套Icon时用这种方式，XML中不要配置app:tabIconTint="@color/your_icon_tint_color"tab?.icon = when(tab?.position) {0 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_home_selected)1 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_category_selected)2 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_profile_selected)else -> null}}override fun onTabUnselected(tab: TabLayout.Tab?) {// 一套Icon时用这种方式//tab?.icon?.setTint(ContextCompat.getColor(applicationContext, R.color.your_icon_tint_color))// 两套Icon时用这种方式，XML中不要配置app:tabIconTint="@color/your_icon_tint_color"tab?.icon = when(tab?.position) {0 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_home_default)1 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_category_default)2 -> ContextCompat.getDrawable(this@TabBarActivity, R.drawable.ic_profile_default)else -> null}}override fun onTabReselected(tab: TabLayout.Tab?) {// Do nothing}})}private inner class ViewPagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {override fun getItemCount(): Int {return 3}override fun createFragment(position: Int): Fragment {return when(position) {0 -> HomeFragment()1 -> CategoryFragment()2 -> ProfileFragment()else -> Fragment()}}}}<?xml version="1.0" encoding="utf-8"?>
<LinearLayoutxmlns: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:orientation="vertical"><androidx.viewpager2.widget.ViewPager2android:id="@+id/viewPager"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1" /><com.google.android.material.tabs.TabLayoutandroid:id="@+id/tabLayout"android:layout_width="match_parent"android:layout_height="wrap_content"app:tabIndicatorColor="@color/your_indicator_color"app:tabSelectedTextColor="@color/your_selected_text_color"app:tabTextColor="@color/your_default_text_color"app:tabIconTint="@color/your_icon_tint_color"app:tabMode="fixed"app:tabGravity="fill"app:tabIndicatorHeight="0dp"app:tabRippleColor="@android:color/transparent" /></LinearLayout><resources>......<color name="your_indicator_color">#FF0000</color><color name="your_selected_text_color">#FF3700B3</color><color name="your_default_text_color">#FFBB86FC</color><color name="your_icon_tint_color">#FFBB86FC</color>
</resources>示意图：
