Android编程开发从零开始编写一个轻量级浏览器

既然是浏览器，按照国际按理先实现一个多窗口的功能我打算用ViewPager+Fragment来实现，但仔细想想，这样缺点是十分明显因为要保证Fragment不

既然是浏览器，按照国际按理先实现一个多窗口的功能

我打算用ViewPager+Fragment来实现，但仔细想想，这样缺点是十分明显因为要保证Fragment不销毁重建，当viewpager的fragment个数过多，会造成很明显的卡顿，所以先用FragmentManager试试效果

返回栈

多窗口中，每一个窗口都有自己的返回栈

每个返回栈都有自己的 fragmentManager，因此这里使用一个无ui的Fragment作为返回栈的载体

/**
 * @author huangweiliang
 */
class NavHostFragment(var name: String, var windowIndex: Int): Fragment() {
    private lateinit var binding: FragmentNavHostBinding
    private val TAG: String = "NavHostFragment"
    var curSelectFragment: Fragment? = null
    var curChildFragmentManager: FragmentManager? = null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        //点击返回键，将当前栈的Fragment作出栈处理
        requireActivity().onBackPressedDispatcher.addCallback(this, object : OnBackPressedCallback(true) {
            override fun handleOnBackPressed() {
                isEnabled = childFragmentManager.backStackEntryCount > 0
                if (isEnabled) childFragmentManager.popBackStackImmediate()
//                else requireActivity().onBackPressedDispatcher.onBackPressed()
                else requireActivity().finish()
            }
        })
    }
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_nav_host, container, false)
        binding = FragmentNavHostBinding.bind(view)
        return view
    }
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        var tag = name
        //创建窗口的第一个页面，即首页Fragment
        if (childFragmentManager.findFragmentByTag(tag) == null) {

            //这里使用的是childFragmentManager
            childFragmentManager.commitNow {
                val multiChildFragment = MultiChildFragment(name, 1, this@NavHostFragment)
                add(R.id.content, multiChildFragment, tag) //不能使用replace，否则每次返回都要重建
            }
        }
        Log.i(TAG, "$name: onViewCreated")
    }
    override fun onStart() {
        super.onStart()
        Log.i(TAG, "$name: onStart")
    }
    override fun onResume() {
        super.onResume()
        Log.i(TAG, "$name: onResume")
    }
    override fun onPause() {
        super.onPause()
        Log.i(TAG, "$name: onPause")
    }
    override fun onDestroy() {
        super.onDestroy()
        Log.i(TAG, "$name: onDestroy")
    }
}

FragmentNavHostBinding

<androidx.fragment.app.FragmentContainerView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/content"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</androidx.fragment.app.FragmentContainerView>

搜索页面暂时放一个EditView

<?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:layout_width="match_parent"
    android:layout_height="match_parent">
    <EditText
        android:id="@+id/ed_search"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="166dp"
        android:layout_marginEnd="16dp"
        android:padding="12dp"
        android:background="@drawable/gray_rounded_shape"
        android:drawableLeft="@drawable/ic_search_gray_24dp"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

/**
 * @author huangweiliang
 * @date 2021/12/9
 * 多窗口中，具体展示的每一个Fragment
 */
class MultiChildFragment(var name: String, var depth: Int, var hostFragment: Fragment) : Fragment() {
    private lateinit var binding: FragmentMultiChildBinding
    val TAG = "MultiChildFragment"
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        Log.i(TAG, "$name-$depth: onCreateView")
        val view = inflater.inflate(R.layout.fragment_multi_child, container, false)
        binding = FragmentMultiChildBinding.bind(view)
        //这里做一简单的传参显示当前页面
        binding.edSearch.text.append("$name-$depth")
        init()
        return view
    }
    private fun init() {
    }
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        Log.i(TAG, "$name-$depth: onViewCreated")
    }
    }

再写一个包含多个返回栈的父Fragment

MultiStackParentFragment

class MultiStackParentFragment: Fragment() {
    companion object {
        fun newInstance() = MultiStackParentFragment()
    }
    private lateinit var binding: FragmentMultiStackParentBinding
    private var windowNum: Int = 0
    /**
     * 当前窗口的Index
     */
    private var curWindowIndex: Int = 0
    /**
     * 记录创建的所有窗口对象
     */
    private val mStackList = ArrayList<NavHostFragment>()
    /**
     * 返回栈顺序,存储返回栈id
     */
    private val mOrderStack = ArrayDeque<Int>()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_multi_stack_parent, container, false)
        binding = FragmentMultiStackParentBinding.bind(view)
        init()
        return view
    }
    private fun init() {
    }
}

在里面实现添加窗口

childFragmentManager管理着以该Fragment作为父容器的所有子Fragment

private fun addWindow() {
    childFragmentManager.commitNow {
        //NavHostFragment代表一个窗口对象
        val navHostFragment = NavHostFragment("窗口${++windowNum}", windowNum)
        curWindowIndex = windowNum
        mStackList.add(navHostFragment)
        add(R.id.content_fragment, navHostFragment) //添加窗口
    }
    transWindowIndex(curWindowIndex)
}