android – BottomNavigationView滞后于片段事务

问题

我在我的一个活动中使用Android设计支持库中的BottomNavigationView,以及每个导航项的Fragments.

每次我在栏上选择一个项目时,我都会进行片段交易,就像下面的片段一样(为简洁起见,代码的某些部分被删除)：

private var fragmentToSet: Fragment? = null

private val onNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->

    fragmentToSet = when (item.itemId) {
        // Choose fragment based on selection
        // ...
    }

// ...

supportFragmentManager.beginTransaction()
                .replace(R.id.container, fragmentToSet)
                .commit()
}

问题是……底栏动画变得超级滞后,只有在片段完全加载并在屏幕上显示后才能完成.

这个问题is not exactly new因为它也可以在使用导航菜单时发生,但至少可以通过使用DrawerLayout.DrawerListener来解决它并仅在抽屉关闭后进行实际的Fragment事务.

到目前为止我尝试过的

我试图“缓存”片段,保留它们的引用以避免每次都重新创建对象(例如MyFragment.newInstance()),但这不起作用.

我也尝试使用处理程序,这有点解决了这个问题,但它可能会导致我遇到异常in some cases.类似下面的代码片段：

handler.postDelayed({changeFragment(fragmentToSet!!)}, 200)

有没有办法在不使用处理程序(或其他异步调用)的情况下解决此问题,在使用导航菜单时与this solution类似？

我通过使用片段管理器隐藏和显示片段来处理这种情况.我写了一个示例代码来处理它,如下所示.

class MainActivity : BaseActivity() {

    private val homeFragment = HomeFragment.newInstance()
    private val categoryFragment = CategoryFragment.newInstance()
    private val searchFragment = SearchFragment.newInstance()

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

        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)
        navigation.menu.findItem(R.id.navigation_home).isChecked = true

        supportFragmentManager.beginTransaction()
                .add(R.id.containerFrameLayout, homeFragment)
                .add(R.id.containerFrameLayout, categoryFragment)
                .add(R.id.containerFrameLayout, searchFragment)
                .commit()
        setTabStateFragment(TabState.HOME).commit()
    }

    override fun onBackPressed() {
        if (supportFragmentManager.backStackEntryCount > 0 || !homeFragment.isHidden) {
            super.onBackPressed()
        } else {
            setTabStateFragment(TabState.HOME).commit()
            navigation.menu.findItem(R.id.navigation_home).isChecked = true
        }
    }

    private fun setTabStateFragment(state: TabState): FragmentTransaction {
        supportFragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE)
        val transaction = supportFragmentManager.beginTransaction()
        transaction.setCustomAnimations(R.anim.fragment_enter, R.anim.fragment_exit)
        when (state) {
            TabState.HOME -> {
                transaction.show(homeFragment)
                transaction.hide(categoryFragment)
                transaction.hide(searchFragment)
            }
            TabState.CATEGORY -> {
                transaction.hide(homeFragment)
                transaction.show(categoryFragment)
                transaction.hide(searchFragment)
            }
            TabState.SEARCH -> {
                transaction.hide(homeFragment)
                transaction.hide(categoryFragment)
                transaction.show(searchFragment)
            }
        }
        return transaction
    }

    private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
        when (item.itemId) {
            R.id.navigation_home -> {
                setTabStateFragment(TabState.HOME).commit()
                return@OnNavigationItemSelectedListener true
            }
            R.id.navigation_category -> {
                setTabStateFragment(TabState.CATEGORY).commit()
                return@OnNavigationItemSelectedListener true
            }
            R.id.navigation_search -> {
                setTabStateFragment(TabState.SEARCH).commit()
                return@OnNavigationItemSelectedListener true
            }
        }
        false
    }

    internal enum class TabState {
        HOME,
        CATEGORY,
        SEARCH,
    }

}