1. FragmentTransaction區(qū)別add和replace

• 源碼中關(guān)于add的解釋

  
  
  截屏2023-03-08 14.40.59.png

• 源碼中關(guān)于replace的解釋

  
  
  截屏2023-03-08 14.45.13.png
  
  

  和明顯,add是把fragment添加到容器中,replace是如果容器中有相同fragment的話,會先移除然后再添加,另外,如果使用add的話,需要配合hide一起使用,生命周期也會有很大不同當(dāng)使用replace的時候,onResume(),onPause(),onStop()這幾個方法會走一次之前的fragment,使用返回鍵的時候,onViewCreated()和onResume()也會執(zhí)行之前add進去的fragment,而使用add和hide()的時候,只會執(zhí)行當(dāng)前fragment的方法,不會執(zhí)行之前fragment的生命周期

2.addToBackStack()這個方法是返回之前fragment的回退棧

下面是一個acitcity中添加多個fragment的代碼:

class ThreeActivity : AppCompatActivity() {
    private  var TAG="TAG"
    private lateinit var binding: ActivityThreeBinding
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding=ActivityThreeBinding.inflate(layoutInflater)
        setContentView(binding.root)
        initView()
    }
    private fun initView(){
        val fragmentOne=FragmentOne()
        supportFragmentManager.beginTransaction().replace(R.id.lv_fragment_container,fragmentOne).commit()
        binding.btBack.setOnClickListener {
            onBackPressed()
        }
    }
}
  override fun onBackPressed() {
        if (supportFragmentManager.backStackEntryCount<=0){
            finish()
        }else{
            supportFragmentManager.popBackStack()
        }
    }

fragment 的代碼

class FragmentOne:Fragment() {
    private  var TAG="TAG"
    private lateinit var binding: FragmentThreeBinding
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        binding=FragmentThreeBinding.inflate(inflater,container,false)
        return binding.root
    }

   
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.tvTitle.text="FragmentOne"
        binding.btNext.setOnClickListener {
            val fragmentTwo=FragmentTwo()
            val fragmentTransaction = parentFragmentManager.beginTransaction()
            fragmentTransaction.addToBackStack(null)
            fragmentTransaction.replace(R.id.lv_fragment_container,fragmentTwo)
            fragmentTransaction.commit()
        }
    }
}

class FragmentTwo:Fragment() {
    private  var TAG="TAG"

    private lateinit var binding: FragmentThreeBinding
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        binding=FragmentThreeBinding.inflate(inflater,container,false)
        return binding.root
    }
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.tvTitle.text="FragmentTwo"
        binding.btNext.setOnClickListener {
            val fragmentTwo=FragmentThree()
            val fragmentTransaction = parentFragmentManager.beginTransaction()
            fragmentTransaction.addToBackStack(null)
            fragmentTransaction.replace(R.id.lv_fragment_container,fragmentTwo)
            fragmentTransaction.commit()
        }
    }