kotlin泛型相關(guān) -> reified

1.reified的作用

https://github.com/JetBrains/kotlin/blob/master/spec-docs/reified-type-parameters.md

支持通過方法傳遞的類型運(yùn)行時(shí)可用可達(dá)

由于java泛型是偽泛型,為了兼容java1.5以前的版本,java運(yùn)行時(shí),會(huì)泛型擦除會(huì)擦除為泛型上界,如果沒有泛型上界會(huì)擦除為Object,所以jvm在程序運(yùn)行時(shí)是不知道泛型的真實(shí)類型, reifield 能保證運(yùn)行時(shí)依然能拿到泛型的具體類型.(當(dāng)前只限制支持內(nèi)聯(lián)函數(shù)可用)

# Reified Type Parameters

Goal: support run-time access to types passed to functions, as if they were reified (currently limited to inline functions only).

## Syntax

A type parameter of a function can be marked as `reified`:



inline fun foo<reified T>() {}

2.實(shí)際使用

Activity定義擴(kuò)展函數(shù)


inline fun <reified T : Activity> Activity.startActivityKtx() {
    this.startActivity(Intent(this, T::class.java))
}

inline fun <reified T : Activity> Activity.startActivityKtxWithParam(block: (intent: Intent) -> Any) {
    val intent = Intent(this, T::class.java)
    block.invoke(intent)
    this.startActivity(intent)
}

調(diào)用

//跳轉(zhuǎn)Activity 帶參數(shù)
startActivityKtxWithParam<TemplateListActivity> {
                            it.putExtra(TemplateListActivity.KEY_CATEGORY_NAME, datas[position].categoryName)
                        }
                        
                        
 //跳轉(zhuǎn)Activity   不帶參數(shù)                    
startActivityKtx<MoreActivity>()

如果不用reifield 我們的寫法是

fun Activity.startActivityKtx(cls: Class<*>) {
    this.startActivity(Intent(this, cls))
}

調(diào)用是

  startActivityKtx(Intent(this, MoreActivity::class.java))

String定義擴(kuò)展函數(shù)

inline fun <reified T> String.jsonToObj(): T? {
    return try {
        val g = Gson()
        val type = object : TypeToken<T>() {}.type
        g.fromJson<T>(this, type)
    } catch (e: Exception) {
        null
    }
}


inline fun <reified T> String.jsonToObjList(): ArrayList<T>? {
    return try {
        val g = Gson()
        val type = object : TypeToken<ArrayList<T>>() {}.type
        return g.fromJson<ArrayList<T>>(this, type)
    } catch (e: Exception) {
        null
    }
}

json string直接轉(zhuǎn)對(duì)象

1.json 格式

[
  {
    "pic": "classic_08",
    "name": "classic"
  },
  {
    "pic": "polygon_04",
    "name": "polygon"
  },
  {
    "pic": "quote_02",
    "name": "quote"
  },
  {
    "pic": "simple_03",
    "name": "simple"
  },
  {
    "pic": "travel_07",
    "name": "travel"
  },
  {
    "pic": "marble_06",
    "name": "marble"
  },
  {
    "pic": "cloud_08",
    "name": "cloud"
  },
  {
    "pic": "freedom_03",
    "name": "freedom"
  }
]

2.bean

@Parcelize
data class TemplateCategoryItemInfo(@SerializedName("pic") var categoryCoverPic: String, @SerializedName("name") var categoryName: String) : Parcelable

3.string 2 bean (assets2String.jsonToObjList())

class CategoryModel : IModel {

    fun getData(): ArrayList<TemplateCategoryItemInfo>? {
        val assets2String = ResourceUtils.readAssets2String("category.json")
        return assets2String.jsonToObjList()
    }
}

不使用reifeild

fun <T> String.jsonToObj2(): T? {
    return try {
        val g = Gson()
        val type = object : TypeToken<T>() {}.type
        g.fromJson<T>(this, type)
    } catch (e: Exception) {
        null
    }
}