BaseFragment 与视图绑定

Question

要在 Android 应用程序中使用 viewbinding，我基本上是为 Activity 和 Fragment 创建基类，以删除每次编写膨胀代码的样板。

活动：

BaseActivity 与viewbinding：

abstract class BaseActivity<VB : ViewBinding> : AppCompatActivity() {
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = getViewBinding()
    }

    abstract fun getViewBinding(): VB

}

MainActivity:

class MainActivity : BaseActivity<ActivityMainBinding>() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(binding.root)
        //we can directly use binding now and it works fine inside activity
        //binding.view.doSomething() 
    }

 override fun getViewBinding(): ActivityMainBinding = ActivityMainBinding.inflate(layoutInflater)
}

片段：

BaseFragment:

abstract class BaseFragment<VB : ViewBinding> : Fragment() {

    var binding: VB? = null

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding = getViewBinding(view)
    }

    abstract fun getViewBinding(view: View): VB
}

DemoFragment:

class DemoFragment : BaseFragment<DemoFragmentBinding>() {

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        //problem is here
        binding.txtData.text="Something"
    }

    override fun getViewBinding(view: View): DemoFragmentBinding = DemoFragmentBinding.bind(view)

}

demo_fragment.xml：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.fragments.DemoFragment">

    <TextView
        android:id="@+id/txt_data"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="Hello" />

</FrameLayout>

问题：无法使用 Demofragment 中的绑定访问视图。我不知道为什么它适用于活动而不适用于片段。

我不想做的第二种方式：

实现 'androidx.fragment:fragment-ktx:1.3.1'

class DemoFragment : Fragment(R.layout.demo_fragment) {

    lateinit var binding: DemoFragmentBinding

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding = DemoFragmentBinding.bind(view).apply {
            txtData.text = "Hello World"
        }
    }
}

Answer 1

您需要在 BaseFragment 中覆盖 onCreateView 并初始化视图绑定

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    _binding = getViewBinding()
    return binding.root
}

那就改这一行

override fun getViewBinding(view: View): DemoFragmentBinding = DemoFragmentBinding.bind(view)

与

override fun getViewBinding() = DemoFragmentBinding.inflate(layoutInflater)

BaseFragment：

abstract class BaseFragment<VB : ViewBinding> : Fragment() {
    private var _binding: VB? = null
    val binding get() = _binding!!

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        _binding = getViewBinding()
        return binding.root
    }

    abstract fun getViewBinding(): VB
}

DemoFragment：

class DemoFragment : BaseFragment<DemoFragmentBinding>() {

    override fun getViewBinding() = DemoFragmentBinding.inflate(layoutInflater)

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        binding.apply {
            txtData.text = "Something"
        }
    }
}

Answer 2

这是用ViewBinding 实现此factory abstraction 的另一种方法。我在下面分享实现代码。我在这里使用genrics。如果有人需要进一步解释，我在这里。确保您已经在build.gradle 文件中启用了viewbinding 功能。然后使用以下BaseFragment.kt 作为您的片段抽象。

BaseFragment：

typealias Inflate<T> = (LayoutInflater, ViewGroup?, Boolean) -> T

abstract class BaseFragment<V: ViewBinding>(
    private val inflate: Inflate<V>
    ) : Fragment() {

    private lateinit var _binding: V
    val binding get() = _binding

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        _binding = inflate(inflater, container, false)
        return binding.root
    }
}

N:B：进一步了解typealias。

HomeFragment：

// Implement the BaseFragment like below
class HomeFragment : BaseFragment<FragmentHomeBinding>(FragmentHomeBinding::inflate) {

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        // usages by calling public variable 'binding' from base class
        binding.message.text = "update $value"
    }
}

Answer 3

我查看了文档，我不确定这是否会破坏您对 BaseFragment 中抽象模式的要求，但我使用此更改测试了您的代码并且它有效。唯一的变化是DemoFragment：

//Add this for the onCreateView implementation
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
        binding = DemoFragmentBinding.inflate(LayoutInflater.from(context), null, false)
        val view = binding!!.root
        return view
    }

然后我在onViewCreated进行测试：

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        //problem is here
        binding?.txtData?.text="Something"

    }

它奏效了。我查看的文档是this section

我认为这样做仍然可以让你避免一些样板，但 onCreateView 覆盖对于每个片段都是必要的，因为不同的视图绑定膨胀（例如DemoFragmentBinding.inflate etc etc）

Answer 4

使用https://github.com/hoc081098/ViewBindingDelegate

abstract class BaseFragment<VB : ViewBinding>(@LayoutRes layoutId: Int) : Fragment(layoutId) {
  protected abstract val binding: VB
}


import com.hoc081098.viewbindingdelegate.*
class MainFragment: BaseFragment<FragmentMainBinding>(R.layout.fragment_main) {
  override val binding by viewBinding()
}