导航组件,控制何时显示汉堡包或后退图标

我有以下活动

class MainActivity : AppCompatActivity() {

private lateinit var drawerLayout: androidx.drawerlayout.widget.DrawerLayout

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

    drawerLayout = drawer_layout

    val navCOntroller= Navigation.findNavController(this, R.id.fragment_main_navHost)

    setSupportActionBar(toolbar)

    NavigationUI.setupActionBarWithNavController(this, navController, drawerLayout)
    navView_main.setupWithNavController(navController)
}

override fun onSupportNavigateUp(): Boolean {
    return NavigationUI.navigateUp(drawerLayout,
        Navigation.findNavController(this, R.id.fragment_main_navHost))
}

override fun onBackPressed() {
    if (drawerLayout.isDrawerOpen(GravityCompat.START)) {
        drawerLayout.closeDrawer(GravityCompat.START)
    } else {
        super.onBackPressed()
    }
}

你可以看到它与导航图相关联,我正在使用导航抽屉.当我浏览抽屉中的项目时,我想保留汉堡图标,只有当我点击片段或弹出窗口中的项目时才将其更改为上/后按钮,并确保系统的行为反映了什么用户期望基于显示的图标.那可能吗

若要控制何时向上/向后显示AppBar导航，需要完成以下操作

1-创建AppBarConfiguration并将其传递给顶级目标和抽屉布局

    appBarCOnfiguration= AppBarConfiguration(
        setOf(
            R.id.dest_one,
            R.id.dest_two
        ),
        drawerLayout
    )

2-告诉AppBar有关配置和导航的信息。这将有助于显示标题并显示箭头或抽屉菜单图标

setupActionBarWithNavController(navController, appBarConfig)

3-最后，重写onOptionsItemSelected和onSupportNavigateUp以及Navigation Component扩展，以通知AppBar如何运行

    override fun onOptionsItemSelected(item: MenuItem)= item.onNavDestinationSelected(findNavController(R.id.my_nav_host_fragment))
        || super.onOptionsItemSelected(item)


override fun onSupportNavigateUp() = findNavController(R.id.my_nav_host_fragment).navigateUp(appBarConfiguration)

参考Google Code Lab导航导航Codelab

遵循这个步骤

1. 与您绑定NavigationViewNavigationUI

NavigationUI.setupWithNavController(nav_view, hostFragment.navController)

2.绑定 ActionBar随着NavController

NavigationUI.setupActionBarWithNavController(this@NavActivity, hostFragment.navController)

3.绑定ActionBar 并DrawerLayout与NavController

NavigationUI.setupActionBarWithNavController(this@NavActivity, hostFragment.navController, drawer_layout)

4.onSupportNavigateUp()在您的活动中覆盖

override fun onSupportNavigateUp(): Boolean {
    return NavigationUI.navigateUp(drawer_layout, hostFragment.navController) 
              || super.onSupportNavigateUp()
}

样品：

class NavActivity : AppCompatActivity(), NavigationView.OnNavigationItemSelectedListener {

    lateinit var hostFragment: NavHostFragment

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_nav)
        setSupportActionBar(toolbar)

        fab.setOnClickListener { view ->
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show()
        }

        val toggle = ActionBarDrawerToggle(
                this, drawer_layout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close)
        drawer_layout.addDrawerListener(toggle)
        toggle.syncState()

        nav_view.setNavigationItemSelectedListener(this)

        hostFragment = supportFragmentManager.findFragmentById(R.id.my_nav_host_fragment) as NavHostFragment    
        NavigationUI.setupWithNavController(nav_view, hostFragment.navController)    
        NavigationUI.setupActionBarWithNavController(this@NavActivity, hostFragment.navController)    
        NavigationUI.setupActionBarWithNavController(this@NavActivity, hostFragment.navController, drawer_layout)    
    }

    override fun onBackPressed() {
        if (drawer_layout.isDrawerOpen(GravityCompat.START)) {
            drawer_layout.closeDrawer(GravityCompat.START)
        } else {
            super.onBackPressed()
        }
    }

    override fun onSupportNavigateUp(): Boolean {
        return NavigationUI.navigateUp(drawer_layout, hostFragment.navController) || super.onSupportNavigateUp()
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        // Inflate the menu; this adds items to the action bar if it is present.
        menuInflater.inflate(R.menu.nav, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        when (item.itemId) {
            R.id.action_settings -> return true
            else -> return super.onOptionsItemSelected(item)
        }
    }

    override fun onNavigationItemSelected(item: MenuItem): Boolean {
        // Handle navigation view item clicks here.
        drawer_layout.closeDrawer(GravityCompat.START)
        return true
    }
}

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