Android 自定义view中实现LifecycleOwner

前言

Google官方提供的Activity和Fragment都默认实现了LifecycleOwner，而使用LiveData一般又都是在Activity和Fragment类中使用，因为在调用LiveData的Observer方法时需要传一个LifecycleOwner对象，而我们自定义的view中没有实现这个接口，所以在自定义view中使用LiveData往往需要传递一个Activity或者Fragment的对象才行，使用起来比较麻烦。网上找了一圈也没几个写自定义View中该如何实现自己的LifecycleOwner，本篇文章就介绍如何在自定义的view中简单的实现当前view的LifecycleOwner。

实现

代码很少，直接贴代码吧

package com.android.car.aidlclient

import android.content.Context
import android.util.AttributeSet
import android.util.Log
import androidx.constraintlayout.widget.ConstraintLayout
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.LifecycleRegistry
import androidx.lifecycle.MutableLiveData

/**
 * @author 杜宗宁
 * @date 2021/12/23 11:02
 * @description TODO
 */
class LifecycleView : ConstraintLayout, LifecycleOwner {
    constructor(context: Context) : super(context)
    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int, defStyleRes: Int) : super(
        context, attrs, defStyleAttr, defStyleRes
    )

    private val liveData = MutableLiveData<Int>()
    private val mRegistry = LifecycleRegistry(this)

    override fun onFinishInflate() {
        super.onFinishInflate()
        postInt()
        liveData.observe(this, {
            Log.d("zdu__", "打印Int：$it")
        })
    }

    private fun postInt() {
        postDelayed({
            liveData.value = 1
            postInt()
        }, 1000)
    }

    override fun onAttachedToWindow() {
        super.onAttachedToWindow()
        mRegistry.currentState = Lifecycle.State.CREATED
        Log.d("zdu__", "view 创建")
    }

    override fun onDetachedFromWindow() {
        super.onDetachedFromWindow()
        mRegistry.currentState = Lifecycle.State.DESTROYED
        Log.d("zdu__", "view 销毁")
    }

    override fun onWindowVisibilityChanged(visibility: Int) {
        super.onWindowVisibilityChanged(visibility)
        if (visibility == VISIBLE) {
            mRegistry.handleLifecycleEvent(Lifecycle.Event.ON_START)
            mRegistry.handleLifecycleEvent(Lifecycle.Event.ON_RESUME)
            Log.d("zdu__", "view 显示")
        }else if (visibility == GONE || visibility == INVISIBLE){
            mRegistry.handleLifecycleEvent(Lifecycle.Event.ON_PAUSE)
            mRegistry.handleLifecycleEvent(Lifecycle.Event.ON_STOP)
            Log.d("zdu__", "view 隐藏")
        }
    }

    override fun getLifecycle(): Lifecycle {
        return mRegistry
    }
}

原理很简单，实现LifecycleOwner接口，重写getLifecycle()方法，返回一个创建的LifecycleRegistry对象，然后在onAttachedToWindow()和onDetachedFromWindow()分别设置当前的状态，在onWindowVisibilityChanged()中判断显示和隐藏，分别发送当前状态，就OK了。

最终实现效果：

订阅关系可以跟随View的生命周期，效果同Activity和Fragment使用。