如何在不同Fragment的自定义View间共享Activity级ViewModel？

你的核心问题是findViewTreeViewModelStoreOwner()会返回包裹自定义View的Fragment（最近的ViewModelStoreOwner），导致每个Fragment下的自定义View拿到的是Fragment级的ViewModel实例，而非Activity级的共享实例。下面是几种可行的解决办法：

方法一：手动传递Activity的ViewModelStoreOwner #

在Fragment中拿到Activity级的ViewModelStoreOwner，直接传递给自定义View：

1. 自定义View中添加方法接收ViewModelStoreOwner

class MyCustomView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0
) : View(context, attrs, defStyleAttr) {

    private lateinit var viewModelStoreOwner: ViewModelStoreOwner
    private val mainViewModel by lazy {
        ViewModelProvider(viewModelStoreOwner).get<MainViewModel>()
    }

    // 暴露方法给Fragment设置ViewModelStoreOwner
    fun setViewModelStoreOwner(owner: ViewModelStoreOwner) {
        this.viewModelStoreOwner = owner
    }
}

2. 在Fragment中初始化自定义View时传入Activity实例

class MyFragment : Fragment() {
    private val mainViewModel: MainViewModel by activityViewModels()

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        val customView = view.findViewById<MyCustomView>(R.id.my_custom_view)
        // 传入Activity作为ViewModelStoreOwner
        customView.setViewModelStoreOwner(requireActivity())
    }
}

方法二：自动向上查找Activity作为ViewModelStoreOwner #

写一个扩展函数，从当前View向上遍历，找到所属的Activity（Activity本身实现了ViewModelStoreOwner接口）：

1. 添加扩展函数

fun View.findActivityViewModelStoreOwner(): ViewModelStoreOwner? {
    var currentContext = context
    while (currentContext is ContextWrapper) {
        if (currentContext is ViewModelStoreOwner) {
            return currentContext
        }
        currentContext = currentContext.baseContext
    }
    return null
}

2. 自定义View中使用该扩展函数初始化ViewModel

class MyCustomView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0
) : View(context, attrs, defStyleAttr) {

    private val mainViewModel by lazy {
        val owner = findActivityViewModelStoreOwner()!!
        ViewModelProvider(owner).get<MainViewModel>()
    }
}

原方法失效原因 #

findViewTreeViewModelStoreOwner()的逻辑是查找当前View树中最近的ViewModelStoreOwner实现组件，而Fragment本身也实现了该接口，所以自定义View会优先绑定到包裹它的Fragment，导致创建Fragment级的ViewModel，无法跨Fragment共享。

内容的提问来源于stack exchange，提问作者Greelings