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,會泛型擦除 會擦除為泛型上界,如果沒有泛型上界會擦除為Object,所以jvm在程序運(yùn)行時是不知道泛型的真實(shí)類型, reifield 能保證運(yùn)行時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
}
}
jsonToObj不使用reifeild.png
可以看出Gson 在解析時是沒有判斷出泛型T的真實(shí)類型的
使用reifeild
jsonToObj使用reifeild.png
