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5. Fragment

5. Fragment

1. Fragment 和 Fragment 的生命周期

1. Fragment

  • Fragment 是一种可以嵌入在 Activity 当中的 UI 片段
  • 应用
    • 使用 RecyclerView 展示一组新闻标题，点开新闻标题后有新闻详情
    • 在手机中，新闻标题列表放在一个 Activity 中，将新闻的详细内容放在另一个 Activity 中，即两个 Activity
    • 在平板中，将新闻标题列表界面和新闻详细内容界面分别放在两个 Fragment 中， 然后在同一个 Activity 里引入这两个 Fragment

2. 生命周期

  • Fragment 生命周期与 Activity 几乎类似

    • 相似点，与 Activity 关联的 Fragment，如果 Activity 处于某一状态，则该 Fragment 也处于该状态
      • 运行状态
      • 暂停状态
      • 停止状态
      • 销毁状态
    • 区别
      • 将 Fragment 从 Activity 中移除时
        • 如果调用了 addToBackStack，则进入停止状态
        • 如果没调用 addToBackStack，则进入销毁状态
          • 即将 Fragment 添加进返回栈后再移除，处于运行但是不可见的状态（停止状态）

  • onAttach()：当 Fragment 和 Activity 建立关联时调用。

  • onCreateView()：为 Fragment 创建视图（加载布局）时调用。

  • onActivityCreated()：确保与 Fragment 相关联的 Activity 已经创建完毕时调用。

  • onDestroyView()：当与 Fragment 关联的视图被移除时调用。

  • onDetach()：当 Fragment 和 Activity 解除关联时调用。

  1. 启动 Activity 和 Fragment
    • onAttach()、 onCreate()、onCreateView()、onActivityCreated()、onStart() 和 onResume()
  2. 切换为另一个 Fragment （使用addToBackStack）
    • onPause()、onStop() 和 onDestroyView()
  3. 返回之前的 Fragment
    • onCreateView()、onActivityCreated()、onStart() 和 onResume()
  4. 退出程序
    • onPause()、onStop()、onDestroyView()、onDestroy() 和 onDetach()

2. 动态加载布局

  • 在不同文件夹下，建立相同的 layout 文件，就能自动选择对应的布局
    • 限定符
      • 【截图】
    • 最小宽度限定符（smallest-width qualifier）
      • layout-sw600sp
        • 单位为 dp
        • 宽度大于等于 600 dp 的设备加载 layout-sw600dp/xxx 的布局
        • 小于的加载 layout/xxx 的布局

3. 代码

  • Fragment

    • 可以直接存放 Fragment

  • FrameLayout

    • 可以动态加载 Fragment

  • 修改代码

    • MainActivity2

      • package com.example.helloworld

import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.util.Log
import android.widget.ArrayAdapter
import android.widget.Button
import android.widget.ListView
import androidx.appcompat.app.AppCompatActivity
import androidx.appcompat.widget.Toolbar


class MainActivity2 : BaseActivity() {

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

        // toolbar 部分
        val toolbar: Toolbar = findViewById(R.id.toolbar2)
        setSupportActionBar(toolbar)
        supportActionBar?.setDisplayHomeAsUpEnabled(true)            // 设置返回按钮
        toolbar.setNavigationOnClickListener { finish() }             // 设置结束 act2

        ActivityCollector.addActivity(this)

        // 从前一个 Activity 接收数据
        val extraData1 = intent.getStringExtra("param1")
        val extraData2 = intent.getStringExtra("param2")
        Log.d("Activity2", "param1 is $extraData1, param2 is $extraData2")


        // 返回数据（但是未实现）
        val button2: Button = findViewById(R.id.button2)        // 通过 id 找到 view, 并指明类型为 button
        button2.setOnClickListener {
            val intent = Intent().apply { putExtra("data_return", "Hello Activity1") }
            setResult(RESULT_OK, intent)
            finish()
        }

        // 关闭所有 Activity
        val button3: Button = findViewById(R.id.button3)
        button3.setOnClickListener {
            ActivityCollector.finishAll()
        }

        val button4: Button = findViewById(R.id.button4)
        button4.setOnClickListener {
            startNewActivity(this, MainActivity3::class.java)
        }

        val button5: Button = findViewById(R.id.button5)
        button5.setOnClickListener {
            startNewActivity(this, MainActivity4::class.java)
        }

        val button7: Button = findViewById(R.id.button7)
        button7.setOnClickListener {
            startNewActivity(this, FragmentActivity::class.java)
        }

    }


}

    • second_layout

      • <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
    android:layout_width="match_parent"
  android:layout_height="match_parent">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        android:minHeight="?attr/actionBarSize"
        android:theme="?attr/actionBarTheme" />

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Back" />

    <Button
        android:id="@+id/button3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Quit App" />

    <Button
        android:id="@+id/button4"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Go third" />

    <Button
        android:id="@+id/button5"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Go forth" />

    <Button
        android:id="@+id/button7"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Go Fragment" />

</LinearLayout>

  • 新增代码

    • FragmentActivity

      • package com.example.helloworld

import android.os.Bundle
import android.util.Log
import android.widget.Button
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.activity.enableEdgeToEdge
import androidx.appcompat.app.AppCompatActivity
import androidx.appcompat.widget.Toolbar
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.material3.Scaffold
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.tooling.preview.Preview
import androidx.fragment.app.Fragment
import com.example.helloworld.AnotherRightFragment.Companion
import com.example.helloworld.ui.theme.HelloWorldTheme

class FragmentActivity : BaseActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.fragment_layout)
        ActivityCollector.addActivity(this)

        val button6: Button = findViewById(R.id.button6)        // button6 在 Fragmentlayout 里面的 Fragment 中，但是会报错
        button6.setOnClickListener {
            replaceFragment(AnotherRightFragment())
        }
        replaceFragment(RightFragment())


        // 交互
        val leftFragment = LeftFragment.newInstance("a","")
        leftFragment.fragmentLog()
        val leftFragment2 = supportFragmentManager.findFragmentById(R.id.leftFrag) as? LeftFragment
        leftFragment2?.fragmentLog()
        val anotherFragment = AnotherRightFragment.newInstance("a","")
        anotherFragment.fragmentLog()
        val rightFragment = supportFragmentManager.findFragmentById(R.id.rightLayout) as? RightFragment
        rightFragment?.fragmentLog() // 没有打印

    }

    // 动态添加 Fragment
    private fun replaceFragment(fragment: Fragment) {
        val fragmentManager = supportFragmentManager
        val transaction = fragmentManager.beginTransaction()                    // 开启一个事务
        transaction.replace(R.id.rightLayout, fragment)      // 向对应 FrameLayout 添加 fragment 对象
        transaction.addToBackStack(null)
        transaction.commit()                                                    // 提交事务
    }
    fun fragmentLog() {
        Log.d("FragmentActivity", "call activity from fragment")
    }
}

    • LeftFragment

      • package com.example.helloworld

import android.os.Bundle
import android.util.Log
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup

// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 * Use the [LeftFragment.newInstance] factory method to
 * create an instance of this fragment.
 */
class LeftFragment : Fragment() {
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }

        val fragActivity = activity as? FragmentActivity     // fragment 调用 activity
        fragActivity?.fragmentLog()
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_left, container, false)
    }

    fun fragmentLog() {
        Log.d("LeftFragment", "call fragment from activity")
    }

    companion object {
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment LeftFragment.
         */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            LeftFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }
}

    • RightFragment

      • package com.example.helloworld

import android.os.Bundle
import android.util.Log
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup

// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 * Use the [RightFragment.newInstance] factory method to
 * create an instance of this fragment.
 */
class RightFragment : Fragment() {
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }


    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_right, container, false)
    }

    fun fragmentLog() {
        Log.d("RightFragment", "call fragment from activity")
    }

    companion object {
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment RightFragment.
         */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            RightFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }
}

    • AnotherRightFragment

      • package com.example.helloworld

import android.os.Bundle
import android.util.Log
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup

// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 * Use the [AnotherRightFragment.newInstance] factory method to
 * create an instance of this fragment.
 */
class AnotherRightFragment : Fragment() {
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_another_right, container, false)
    }

    fun fragmentLog() {
        Log.d("AnotherRightFragment", "call fragment from activity")
    }

    companion object {
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment AnotherRightFragment.
         */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            AnotherRightFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }
}

    • fragment_layout

      • <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <fragment
        android:id="@+id/leftFrag"
        android:name="com.example.helloworld.LeftFragment"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1" />

    <FrameLayout
        android:id="@+id/rightLayout"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="3" >
    </FrameLayout>

</LinearLayout>

    • fragment_left

      • <?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".LeftFragment">

    <Button
        android:id="@+id/button6"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="Button" />
</FrameLayout>

    • fragment_right

      • <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:background="#00ff00"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:textSize="24sp"
        android:text="This is right fragment"
        />

</LinearLayout>

    • fragment_another_right

      • <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:background="#ffff00"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:textSize="24sp"
        android:text="This is another right fragment"
        />

</LinearLayout>

【最佳实践和Kotlin知识】

posted @ 2026-01-14 16:10  y丶innocence  阅读(11)  评论(0)    收藏  举报