Kevin Learn Kotlin：Fragment 必知必会

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生命周期

onAttach() → onCreate() → onCreateView() →onActivityCreated() → onStart() → onResume() → onPause() → onStop() → onDestroyView() → onDestroy() → onDetach()

fragment.png

• onAttach()
  当该 Fragment 被添加到 Activity 中会回调，只会被调用一次；

• onCreate()
  创建 Fragment 时回调，只会被调用一次；

• onCreateView()
  每次创建，绘制该 Fragment 的 View 组件时回调，会将显示的 View 返回；

• onActivityCreated()
  当 Fragment 所在的 Activity 启动完成后回调；

• onStart()
  启动 Fragment 时被回调

• onResume()
  恢复 Fragment 时被回调，onStart() 方法后一定回调 onResume() 方法 onStart() 可见，onResume()后才能交互；

• onPause()
  暂停 Fragment 时被回调

• onStop()
  停止 Fragment 时被回调

• onDestroyView()
  销毁该 Fragment 所包含的 View 组件时使用

• onDestroy()
  销毁 Fragment 时被毁掉

• onDetach()
  将该Fragment 从 Activity 被删除/替换完成后回调该方法；onDestroy() 方法后一定会回调该方法；该方法只调用一次

Fragment 的动态添加与数据传递

动态添加 Fragment

// 1、定义 StudyFragment 需要继承自 Fragment, 并且绑定布局文件
class StudyFragment : Fragment(R.layout.fragment_study) {}

// 2、在Activity 中使用
class StudyActivity: AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_study)

        val fragment = StudyFragment()
        val ft = supportFragmentManager.beginTransaction()
        ft.replace(R.id.container,fragment)
        ft.commitAllowingStateLoss()
    }
}

Activity 向 Fragment 中传递数据

class StudyActivity: AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_study)

        val fragment = StudyFragment()
        val bundle = Bundle()
        bundle.putString("name","Kevin")
        bundle.putInt("age",20)
        fragment.arguments = bundle

        val ft = supportFragmentManager.beginTransaction()
        ft.replace(R.id.container,fragment)
        ft.commitAllowingStateLoss()
    }
}

---------------------------------------分割线---------------------------------------
class StudyFragment : Fragment(R.layout.fragment_study) {
    private val TAG = "StudyFragment"
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        val name = arguments?.getString("name")
        val age = arguments?.getInt("age")

        tab_study.text = name
        tab_stable.text = "$age"
    }
}

实例

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需求：实现底部导航栏

1. Activity 页面布局

<?xml version="1.0" encoding="utf-8"?>
<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">

    <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:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />

    <fragment
        android:id="@+id/nav_host_fragment_activity_main"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />

</androidx.constraintlayout.widget.ConstraintLayout>

2. menu/bottom_nav_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:id="@+id/navigation_home"
        android:icon="@drawable/ic_home_black_24dp"
        android:title="@string/title_home" />

    <item
        android:id="@+id/navigation_study"
        android:icon="@mipmap/icon_menu_study"
        android:title="@string/title_study" />

    <item
        android:id="@+id/navigation_dashboard"
        android:icon="@drawable/ic_dashboard_black_24dp"
        android:title="@string/title_dashboard" />

    <item
        android:id="@+id/navigation_notifications"
        android:icon="@drawable/ic_notifications_black_24dp"
        android:title="@string/title_notifications" />

</menu>

3. navigation/mobile_navigation

<?xml version="1.0" encoding="utf-8"?>
<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">

    <fragment
        android:id="@+id/navigation_home"
        android:name="com.hkt.firstapp.ui.home.HomeFragment"
        android:label="@string/title_home"
        tools:layout="@layout/fragment_home" />

    <fragment
        android:id="@+id/navigation_study"
        android:name="com.hkt.firstapp.ui.study.StudyFragment"
        android:label="@string/title_study"
        tools:layout="@layout/fragment_study" />

    <fragment
        android:id="@+id/navigation_dashboard"
        android:name="com.hkt.firstapp.ui.dashboard.DashboardFragment"
        android:label="@string/title_dashboard"
        tools:layout="@layout/fragment_dashboard" />

    <fragment
        android:id="@+id/navigation_notifications"
        android:name="com.hkt.firstapp.ui.notifications.NotificationsFragment"
        android:label="@string/title_notifications"
        tools:layout="@layout/fragment_notifications" />
</navigation>

4. MainActivitry.kt

class MainActivity : AppCompatActivity() {
    private val TAG = "MainActivity"
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)
        val navView: BottomNavigationView = findViewById(R.id.nav_view)

        val navController = findNavController(R.id.nav_host_fragment_activity_main)

        navView.setupWithNavController(navController)

    }
}

5. DashboardFragment.kt

class DashboardFragment : Fragment(R.layout.fragment_dashboard) {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        rv_fruit.layoutManager = GridLayoutManager(context, 3)
        rv_fruit.adapter = MyAdapter()
    }

    inner class MyAdapter : RecyclerView.Adapter<MyViewHolder>(){
        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
            val itemView = LayoutInflater.from(context)
                .inflate(R.layout.item_fruit_grid,parent,false)
            return MyViewHolder(itemView)
        }

        override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
            holder.itemView.iv_fruit.setImageResource(R.mipmap.icon_jetpack)

            holder.itemView.tv_fruit_name.text = "【${position}】Apple"
        }

        override fun getItemCount(): Int {
            return 20
        }

    }

    class MyViewHolder(view: View) : RecyclerView.ViewHolder(view) {}
}