使用ViewBinding（可从Android Studio 3.6获得）时，最佳做法是使 Fragment中的绑定无效onDestroyView。在我们的项目中，我们经常忘记这样做。我们还将复制的绑定逻辑复制粘贴到所有的Fragments中，从而导致代码重复，并在Fragments的方法中添加了大量的空检查。为了清理代码，我们创建了一个ViewBindingHolder类，该类负责绑定的生命周期并提供一些帮助程序方法，以使片段中的代码安全且简短。
这种方法的优点
- 启用对绑定属性的安全访问。
- 使代码简洁明了。
- 在生命周期结束时使绑定无效。
用法
使用ViewBindingHolder需要对Fragment进行两项调整：
class ExampleFragment : Fragment(), ViewBindingHolder<FragmentExampleBinding> by ViewBindingHolderImpl() {
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? = initBinding(FragmentExampleBinding.inflate(layoutInflater), this) {
// do your onCreateView logic here, where 'this' is the binding object.
textTitle.text = "Clean ViewBinding and Lifecycle handling"
}
}
ViewBindingHolder<YourBindingClass> by…将ViewBindingHolder类初始化为Fragment的委托。initBinding在onCreateView中绑定视图。
在onCreateView之外，有两种访问绑定的方法：
1. binding ？
假定绑定可能null是最安全的选择。由于我们使用委托，因此您可以直接从Fragment访问binding属性。
binding?.textTitle.text = “The safest way to access”
2. requireBinding（）
当确定逻辑在片段的视图生命周期内运行时，可以使用requireBinding()。
fun initTitle() = requireBinding() {
// here, 'this' is the 'binding' property.
textTitle.text = "ViewBinding and Lifecycle handling"
}
您也可以在没有代码块的情况下使用它：
fun initTitle() {
val binding = requireBinding()
binding.textTitle.text = "ViewBinding and Lifecycle handling"
}
在requireBinding()Fragment的视图生命周期之外调用时，将抛出IllegalStateException，类似于的行为requireActivity()。
Inside ViewBindingHolder
源码实现，详细参见注视
/**
* Holds and manages ViewBinding inside a Fragment.
*/
interface ViewBindingHolder<T : ViewBinding> {
val binding: T?
/**
* Saves the binding for cleanup on onDestroy, calls the specified function [onBound] with `this` value
* as its receiver and returns the bound view root.
*/
fun initBinding(binding: T, fragment: Fragment, onBound: (T.() -> Unit)?): View
/**
* Calls the specified [block] with the binding as `this` value and returns the binding. As a consequence, this method
* can be used with a code block lambda in [block] or to initialize a variable with the return type.
*
* @throws IllegalStateException if not currently holding a ViewBinding (when called outside of an active fragment's lifecycle)
*/
fun requireBinding(block: (T.() -> Unit)? = null): T
}
class ViewBindingHolderImpl<T : ViewBinding> : ViewBindingHolder<T>, LifecycleObserver {
override var binding: T? = null
var lifecycle: Lifecycle? = null
private lateinit var fragmentName: String
/**
* To not leak memory we nullify the binding when the view is destroyed.
*/
@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
fun onDestroyView() {
lifecycle?.removeObserver(this) // not mandatory, but preferred
lifecycle = null
binding = null
}
override fun requireBinding(block: (T.() -> Unit)?) =
binding?.apply { block?.invoke(this) } ?: throw IllegalStateException("Accessing binding outside of Fragment lifecycle: $fragmentName")
override fun initBinding(binding: T, fragment: Fragment, onBound: (T.() -> Unit)?): View {
this.binding = binding
lifecycle = fragment.viewLifecycleOwner.lifecycle
lifecycle?.addObserver(this)
fragmentName = fragment::class.simpleName ?: "N/A"
onBound?.invoke(binding)
return binding.root
}
}
