Question

我正在尝试通过关注 this straightforward approach 将徽章设置为 BottomNavigationView。

但是，当我初始化 BottomNavigationView 时，我得到：

java.lang.IllegalStateException: view.findViewById(R.id.bottom_navigation_view) must not be null

我正在从片段初始化 BottomNativigationView。我猜这就是问题所在，但我想不出解决方案。

private lateinit var bottomNavigation: BottomNavigationView

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view = inflater.inflate(R.layout.fragment_home, container, false)

    bottomNavigation = view.findViewById(R.id.bottom_navigation_view)
}

这是为片段设置导航的 Activity 的 BottomNavigationView xml。

<com.google.android.material.bottomnavigation.BottomNavigationView
    android:id="@+id/bottom_navigation_view"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/colorWhite"
    app:itemIconTint="@color/navigation_tint"
    app:itemTextColor="@color/navigation_tint"
    app:labelVisibilityMode="labeled"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:menu="@menu/bottom_navigation" />

感觉好像我错过了一些简单的东西，但我不知道是什么。谢谢！

Answer 1

您有许多选项可以在片段之间进行交流 - 活动和片段本身..

您不应该尝试从片段访问活动视图。

解决方案 1：与主机活动共享数据

class ItemViewModel : ViewModel() {
    private val mutableSelectedItem = MutableLiveData<Item>()
    val selectedItem: LiveData<Item> get() = mutableSelectedItem

    fun selectItem(item: Item) {
        mutableSelectedItem.value = item
    }
}


class MainActivity : AppCompatActivity() {
    // Using the viewModels() Kotlin property delegate from the activity-ktx
    // artifact to retrieve the ViewModel in the activity scope
    private val viewModel: ItemViewModel by viewModels()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        viewModel.selectedItem.observe(this, Observer { item ->
            // Perform an action with the latest item data
        })
    }
}

class ListFragment : Fragment() {
    // Using the activityViewModels() Kotlin property delegate from the
    // fragment-ktx artifact to retrieve the ViewModel in the activity scope
    private val viewModel: ItemViewModel by activityViewModels()

    // Called when the item is clicked
    fun onItemClicked(item: Item) {
        // Set a new item
        viewModel.selectItem(item)
    }
}

解决方案 2：在主机活动中接收结果

button.setOnClickListener {
    val result = "result"
    // Use the Kotlin extension in the fragment-ktx artifact
    setFragmentResult("requestKey", bundleOf("bundleKey" to result))
}

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        supportFragmentManager
                .setFragmentResultListener("requestKey", this) { requestKey, bundle ->
            // We use a String here, but any type that can be put in a Bundle is supported
            val result = bundle.getString("bundleKey")
            // Do something with the result
        }
    }
}

还有很多方法，但这些是 Google 的最新方法。

检查此参考：https://developer.android.com/guide/fragments/communicate

Answer 2

您可以通过将 activity 投射到您的活动类，然后扩充视图，从其片段访问活动。

bottomNavigation = (activity as MyActivityName).findViewById(R.id.bottom_navigation_view)

底部导航视图空

2 个答案: