ViewBinding与Kotlin委托

接上篇幅

自定义属性委托的用处很多，例如组合替代继承，给个ViewBinding在Fragment中的使用的例子：

委托:

/**
 * 自定义属性委托。
 *
 * 
......。
 * 

 * 

 * Time    2020/5/18 14:54

 * CopyRight    2020, tt.reducto

 *
 * @version  : 1.0.0
 * @author   : TT
 */

fun  Fragment.viewBindingByLazy(initialise: () -> T): ReadOnlyProperty =
    object : ReadOnlyProperty, DefaultLifecycleObserver {

        private var binding: T? = null

        private var viewLifecycleOwner: LifecycleOwner? = null
        private val mainHandler = Handler(Looper.getMainLooper())


        init {
            this@viewBindingByLazy
                .viewLifecycleOwnerLiveData
                .observe(this@viewBindingByLazy, Observer { newLifecycleOwner ->
                    viewLifecycleOwner
                        ?.lifecycle
                        ?.removeObserver(this)

                    viewLifecycleOwner = newLifecycleOwner.also {
                        it.lifecycle.addObserver(this)
                    }
                })
        }
        @MainThread
        override fun onDestroy(owner: LifecycleOwner) {
            super.onDestroy(owner)
            mainHandler.post {
                binding = null
            }
        }
        @MainThread
        override fun getValue(
            thisRef: Fragment,
            property: KProperty<*>
        ): T {

            return this.binding ?: initialise().also {
                this.binding = it
            }
        }
    }

使用：

class MultipleFragment : Fragment(R.layout.fragment_multiple) {
    .....
    private val binding: FragmentMultipleBinding by viewBindingByLazy {
        FragmentMultipleBinding.bind(
            requireView()
        )
    }
    .....
}

注意添加依赖:

 implementation  "androidx.lifecycle:lifecycle-common-java8:2.2.0"

那我们这里同样利用自定义属性委托让ViewHolder可以存储和检索任何类型的任何属性

by Map委托

/**
 *
 * @receiver View
 * @param id Int
 * @param initializer Function0
 * @return T 存储容器-> map
 */
private inline fun  View.getOrPutTag(@IdRes id: Int, initializer: () -> T) =
    getTag(id) as? T ?: initializer().also {
        setTag(id, it)
    }
    
    
 /**
 *  
 */
private inline val BindingViewHolder<*>.propertyByMap
    get() = itemView.getOrPutTag>(
        R.id.recyclerview_view_binding_map,
        ::mutableMapOf
    )

避免重名

/**
 * 用于ViewBinding的通用ViewHolder。
 *  
 * 
对外提供数据与视图的匹配。
 * 

 * 

 * Time    2020/5/18 12:38

 * CopyRight    2020, tt.reducto

 *
 * @version  : 1.0.0
 * @author   : TT
 */
open class BindingViewHolder private constructor(val binding: T) :
    RecyclerView.ViewHolder(binding.root) {
    constructor(
        parent: ViewGroup,
        creator: (inflater: LayoutInflater, root: ViewGroup, attachToRoot: Boolean) -> T
    ) : this(
        creator(
            LayoutInflater.from(parent.context),
            parent,
            false
        )
    )

    /**
     *  委托
     *
     * @param T itemView适配数据。
     */
    class BindingDataLazy : ReadWriteProperty, T> {
        override fun getValue(thisRef: BindingViewHolder<*>, property: KProperty<*>): T {
            @Suppress("UNCHECKED_CAST")
            return thisRef.propertyByMap[property.name] as T
        }

        override fun setValue(thisRef: BindingViewHolder<*>, property: KProperty<*>, value: T) {
            thisRef.propertyByMap[property.name] = value
        }
    }
}

/**
 *
 * @receiver ViewGroup
 * @param creator 布局生成器
 * @return BindingViewHolder
 */
fun  ViewGroup.getViewHolder(
    creator: (inflater: LayoutInflater, root: ViewGroup, attachToRoot: Boolean) -> T
): BindingViewHolder =
    BindingViewHolder(this, creator)

/**
 *
 */
private inline val BindingViewHolder<*>.propertyByMap
    get() = itemView.getOrPutTag>(
        R.id.recyclerview_view_binding_map,
        ::mutableMapOf
    )

/**
/**
 * getTag()内部使用 { private SparseArray