Android 利用 LiveData 共享数据，进行跨界面数据传递

Posted 2021-11-06 匆忙拥挤repeat

import androidx.lifecycle.MutableLiveData
/**
 * desc:    共享事件，进行跨界面数据传递
 * author:  stone
 * email:   [e-mail]
 * time:    2021/10/15 16:01
 */
class LiveDataBus private constructor() : MutableLiveData<Event<FlashEvent>>() {

    companion object {
        val instance by lazy { LiveDataBus() }
    }
}
// event: 事件类型； data: 要传递的数据
data class FlashEvent(val event: Int, val data: Any) {
    companion object {
        const val EVENT_TEST = 1 // 测试事件
    }
}

LiveDataBus 单例实现，value 可变。
FlashEvent 自定义 事件

---

open class Event<out T>(private val content: T) {

    var hasBeenHandled = false
        private set // Allow external read but not write

    /**
     * Returns the content and prevents its use again.
     */
    fun getContentIfNotHandled(): T? {
        if (!hasBeenHandled) {
            hasBeenHandled = true
            return content
        }

        return null
    }

    /**
     * Returns the content, even if it's already been handled.
     */
    fun peekContent(): T = content
}

import androidx.lifecycle.Observer
class EventObserver<T>(private val onEventUnhandledContent: (T) -> Unit) : Observer<Event<T>> {
    override fun onChanged(event: Event<T>?) {
        event?.getContentIfNotHandled()?.let { value ->
            onEventUnhandledContent(value)
        }
    }
}

Event 提供 getContentIfNotHandled()
EventObserver 结合 Event，实现 onChanged()，未处理事件时才调用传入的函数

---

// 发送事件
LiveDataBus.instance.value = Event(FlashEvent(FlashEvent.EVENT_TEST))
// 处理事件
LiveDataBus.instance.observe(viewLifecycleOwner, EventObserver {
    if (it.event == FlashEvent.EVENT_TEST) {
        // do sth.
    }
})