Android kotlin 委托获取 intent 参数

通过 Kotlin 中的两个接口：ReadOnlyProperty 和 ReadWriteProperty，可以方便的实现属性委托或局部委托。对于 val 变量使用 ReadOnlyProperty，而 var 变量实现ReadWriteProperty。

这里通过 kotlin 实现委托获取界面跳转时 intent 传递的数据：

fun <T> extraActivity(name: String): ActivityExtras<T?> = ActivityExtras(name, null)

fun <T> extraActivity(name: String, defaultValue: T) = ActivityExtras(name, defaultValue)

fun <T> extraFragment(name: String): FragmentExtras<T?> = FragmentExtras(name, null)

fun <T> extraFragment(name: String, defaultValue: T) = FragmentExtras(name, defaultValue)


class ActivityExtras<T>(private val name: String, private val defaultValue: T) :
    ReadOnlyProperty<Activity, T> {

    private var extra: T? = null

    override fun getValue(thisRef: Activity, property: KProperty<*>): T {
        return extra
            ?: thisRef.intent?.extras?.take<T>(name)?.also { extra = it }
            ?: defaultValue.also { extra = it }
    }
}


class FragmentExtras<T>(private val name: String, private val defaultValue: T) :
    ReadOnlyProperty<Fragment, T> {

    private var extra: T? = null

    override fun getValue(thisRef: Fragment, property: KProperty<*>): T {
        return extra
            ?: thisRef.arguments?.take<T>(name)?.also { extra = it }
            ?: defaultValue.also { extra = it }
    }
}


@Suppress("UNCHECKED_CAST")
fun <T> Bundle.take(key: String): T? {
    try {
        return get(key) as? T?
    } catch (e: Exception) {
        e.printStackTrace()
    }
    return null
}

使用姿势：

// 跳转至 activity
val intent = Intent(context, xxx::class.java)
intent.putExtra("name", "candy")
context.startActivity(intent)

// activity 中获取参数
private val mName by extraActivity<String>("name")



// fragment 传递参数
val fragment = XxxFragment()
fragment.arguments = Bundle().apply { putString("name", name) }

// fragment 中获取参数
private val mName by extraFragment<String>("name")

就这么简单。