使用视图绑定导航

Question

我正在尝试使用视图绑定替换所有 findViewById。但是，我无法使用 View Binding 更改我的 NavController 代码行。

val navController = findNavController(this, R.id.mainHostFragment)

到

var binding : ActivityMainBinding
val navController = findNavController(this, binding.mainHostFragment)

我该怎么做？

Answer 1

您不能将其替换为视图绑定。 findNavController 不仅仅是在布局中查找视图。

看看源码here

/**
* Find a {@link NavController} given a local {@link Fragment}.
*
* <p>This method will locate the {@link NavController} associated with this Fragment,
* looking first for a {@link NavHostFragment} along the given Fragment's parent chain.
* If a {@link NavController} is not found, this method will look for one along this
* Fragment's {@link Fragment#getView() view hierarchy} as specified by
* {@link Navigation#findNavController(View)}.</p>
*
* @param fragment the locally scoped Fragment for navigation
* @return the locally scoped {@link NavController} for navigating from this {@link Fragment}
* @throws IllegalStateException if the given Fragment does not correspond with a
* {@link NavHost} or is not within a NavHost.
*/
@NonNull
public static NavController findNavController(@NonNull Fragment fragment) {
Fragment findFragment = fragment;
while (findFragment != null) {
    if (findFragment instanceof NavHostFragment) {
        return ((NavHostFragment) findFragment).getNavController();
    }
    Fragment primaryNavFragment = findFragment.getParentFragmentManager()
            .getPrimaryNavigationFragment();
    if (primaryNavFragment instanceof NavHostFragment) {
        return ((NavHostFragment) primaryNavFragment).getNavController();
    }
    findFragment = findFragment.getParentFragment();
}
// Try looking for one associated with the view instead, if applicable
View view = fragment.getView();
if (view != null) {
    return Navigation.findNavController(view);
}
throw new IllegalStateException("Fragment " + fragment
        + " does not have a NavController set");
}

它不仅仅是找到控制器。它遍历、创建片段、创建视图并抛出异常。

视图绑定只是生成一个绑定类，其中包含您布局的所有视图。它不是用来查找应用的导航控制器的。

Answer 2

在answer 的帮助下，我找到了一个简单的实现

binding?.apply {
        setContentView(root)
        setSupportActionBar(toolbar)
        navController = (supportFragmentManager
            .findFragmentById(fragmentHost.id) as NavHostFragment)
            .navController
        setupActionBarWithNavController(navController, appBarConfiguration)
        bottom.setupWithNavController(navController)
    }

Answer 3

findNavController(R.id.nav_host_fragment) 应该在将视图附加到这样的活动之后：

setContentView(binding.root)
val navController: NavController = findNavController(R.id.nav_host_fragment) 

更多Here

Answer 4

这是我的示例代码，使用视图绑定和导航。

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.fragment.NavHostFragment
import androidx.navigation.ui.AppBarConfiguration
import androidx.navigation.ui.setupActionBarWithNavController
import androidx.navigation.ui.setupWithNavController
import com.zeddigital.zigmaster.databinding.ActivityMainBinding


class MainActivity : AppCompatActivity() {

    private lateinit var appBarConfiguration: AppBarConfiguration
    private lateinit var binding : ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        /*
        Use view binding in activities
        
        Call the static inflate() method included in the generated binding class. 
        This creates an instance of the binding class for the activity to use.
        Get a reference to the root view by either calling the getRoot() method or using Kotlin property syntax.
        Pass the root view to setContentView() to make it the active view on the screen.*/
        binding = ActivityMainBinding.inflate(layoutInflater)

        val view = binding.root
        setContentView(view)

        setSupportActionBar(binding.appBarMain.toolbar)

        //val navController = findNavController(R.id.nav_host_fragment)
        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
        val navController = navHostFragment.navController

        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        appBarConfiguration = AppBarConfiguration(setOf(
                R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow), binding.drawerLayout)
        setupActionBarWithNavController(navController, appBarConfiguration)
        binding.navView.setupWithNavController(navController)

    }
}