如何拆分視圖模型或使用小視圖模型構建主視圖模型？

我有一個相當大的復雜 ViewModel，我想拆分它或用幾個較小的 ViewModel 構建它。

下面我想展示我是如何制作我的 ViewModel 的（請不要笑，這是我的第一個 Android ViewModel）。我沒有使用 DataBinding，只是使用 ViewBinding。

class AssignUserTagToInventoryItemViewModel() : ViewModel() {

    private val UserTag = "MyApp"   this.javaClass.simpleName

    init {
        Log.d(UserTag, "Class init called")
        loadInventoryItems()
        loadRandomUserTags() // todo: replace with real implementation
    }

    private var allItems = ArrayList<InventoryItemDto?>()

    //<editor-fold desc="FilterByName">
    private val _filterByName = MutableLiveData<String>("")
    val filterByName: LiveData<String> get() = _filterByName
    fun setFilterByName(t : String) { _filterByName.value = t; applyFilters();}
    //</editor-fold>

    //<editor-fold desc="FilterByAssignedToMe">
    private val _filterByAssignedToMe = MutableLiveData<Boolean>(false)
    val filterByAssignedToMe: LiveData<Boolean> get() = _filterByAssignedToMe
    fun setFilterByAssignedToMe(t : Boolean) { _filterByAssignedToMe.value = t; applyFilters(); }
    //</editor-fold>

    //<editor-fold desc="SelectedInventoryItem">
    private val _selectedInventoryItem = MutableLiveData<InventoryItemDto?>(null)
    fun getSelectedInventoryItem() : LiveData<InventoryItemDto?> = _selectedInventoryItem
    fun setSelectedInventoryItem(itemDto: InventoryItemDto?) {
        _selectedInventoryItem.value = itemDto
        selectedItemOrUserTagChanged()
    }
    //</editor-fold>

    // <editor-fold desc="FilteredItems">
    val _displayedItems = MutableLiveData<ArrayList<InventoryItemDto?>>(ArrayList())
    val displayedItems: LiveData<ArrayList<InventoryItemDto?>> get() = _displayedItems
    // </editor-fold>

    // <editor-fold desc="ItemsListError">
    val _itemsListError = MutableLiveData<String>("")
    val itemsListError :LiveData<String> get() = _itemsListError
    fun setItemsListError(s : String) { _itemsListError.value = s }
    // </editor-fold>

    //<editor-fold desc="UserTag list">
    val _UserTags = MutableLiveData<ArrayList<UserTag>>(ArrayList())
    val UserTags : LiveData<ArrayList<UserTag>> get() = _UserTags
    fun setUserTags(a : ArrayList<UserTag>) { _UserTags.value = a }
    //</editor-fold>

    //<editor-fold desc="SelectedUserTagItem">
    private val _selectedUserTag = MutableLiveData<UserTag?>(null)
    fun getSelectedUserTag() : LiveData<UserTag?> = _selectedUserTag
    fun setSelectedUserTag(UserTag : UserTag?) {
        _selectedUserTag.value = UserTag
        selectedItemOrUserTagChanged()
    }
    //</editor-fold>

    //<editor-fold desc="CanSubmit">
    private val _canSubmit = MutableLiveData<Boolean>(false)
    val canSubmit: LiveData<Boolean> get() = _canSubmit
    //</editor-fold>

    private fun selectedItemOrUserTagChanged() {
        _canSubmit.value = true
    }

    private fun loadInventoryItems(){
        Log.d(UserTag, "Loading inventory items...")
        viewModelScope.launch {
            try {
                val apiResponse = ApiResponse(ApiAdapter.apiClient.findAllInventoryItems())
                if (apiResponse.code == 200 && apiResponse.body != null) {
                    allItems = apiResponse.body
                    applyFilters()
                    Log.d(UserTag, "Loading inventory items done.")
                }
                else {
                    setItemsListError(apiResponse.code.toString())
                    Log.d(UserTag, "Loading inventory items error.")
                }
            } catch (t : Throwable) {
                setItemsListError(t.message.toString())
            }
        }
    }

    private fun applyFilters(){
        Log.d(UserTag, "ViewModel apply filters called. Current name filter: ${filterByName.value}")

        val tempResults = ArrayList<InventoryItemDto?>()
        val nameFilterLowercase = filterByName.value.toString().lowercase()

        if (!filterByName.value.isNullOrEmpty()) {
            for (item in allItems) {
                val itemNameLowercase = item?.name?.lowercase()?:""
                if (itemNameLowercase.contains(nameFilterLowercase))
                    tempResults.add(item)
            }
            _displayedItems.value = tempResults
        } else {
            _displayedItems.value = allItems
        }
    }

    private fun loadRandomUserTags(){
        val temp = ArrayList<UserTag>()

        for (i in 1..50){
            val epc = getRandomHexString(24).uppercase()

            val UserTag = UserTag(epc,  0, "0")
            temp.add(UserTag)
        }

        viewModelScope.launch {
            delay(100)

            _UserTags.value = temp
        }
    }

    private fun getRandomHexString(numchars: Int): String {
        val r = Random()
        val sb = StringBuffer()
        while (sb.length < numchars) {
            sb.append(Integer.toHexString(r.nextInt()))
        }
        return sb.toString().substring(0, numchars)
    }
}

uj5u.com熱心網友回復：

只需根據他們正在執行的任務創建多個視圖模型。這里有幾個問題：

1. 您的 ViewModel 名稱太長
2. 您可以創建 getRandomHexString 的物件，這樣您就可以在將來可能需要的任何其他類或 ViewModel 中使用它。它還節省了 ViewModel 內部的空間。
3. 了解干凈的架構并遵循其實踐。在這里，您可以創建一個單獨的視圖模型或幫助器類來過濾您的結果。如果您創建另一個視圖模型，您可以簡單地將當前視圖模型的結果檢索到活動并在活動中呼叫過濾器視圖模型。這樣，您可以根據它們所扮演的角色或它們執行的功能來分隔代碼塊。

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