引用时，Kotlin Companion Object为null-Java 学习之路

不确定我是否正确使用此伴侣对象 .

数据类：

data class AppModel(
    val name: String,
    val items: List<ItemModel>,
)

设置数据：

open class PathManager() {

    companion object {
        var shared = PathManager()    // SHARED OBJECT IN QUESTION
    }

    var app: AppModel? = null

    fun setUp() {
        // Show loading...

        // Parse the JSON
        val gson = GsonBuilder().create()
        val text = mainActivity.resources.openRawResource(R.raw.jsonFile)  
            .bufferedReader().use { it.readText() }
        val appModel = gson.fromJson(text, AppModel::class.java)

        app = appModel

        performInitialPath()
    } 

    private fun performInitialPath() {

        val app = app?.let { it } ?: error("Attempted to start without an App Config.")

        this.app = app    // DEBUGGER SHOWS CORRECT VALUES HERE

        // Removed irrelevant code for readability, builds 'initialFoo' here

        this.mainActivity.addFragment(initialFoo)
    }
}

Fragment Builder Class（在这里查找Path Manager伴随对象）：

class Frag : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {

        var itemModels: List<ItemModel>? = null

        if(PathManager.shared.app?.items != null) {  // NULL - WHY?
            itemModels = PathManager.shared.app?.items  
        }
   }
}

总结一下发生了什么：

AppModel在PathManager（）中正确构建 . 那里有数据（可以在调试器中看到）
Path Manager启动'Frag（）'类
Frag（）类引用返回在PathManager（）中创建的伴随对象，尝试在“PathManager.shared.app?.items”中查找数据，但其中的数据为空时，不应该为空 . 伴随对象不是静态变量吗？

我确信我错过了一些东西，只是寻求建议 . 我是否正确调用了伴侣对象？我不能从像这样的新类中引用它吗？是什么赋予了？

1 回答

PathManager.shared.app?.items 始终为null，因为您永远不会将 AppModel 分配给随播对象 . PathManager 中的 var app: AppModel? = null 实例和 PathManager.shared.app 是两个不同的对象 .

要存储静态数据，您可以执行以下操作：

open class PathManager() {

    companion object {
        //Here Don't create object is you dont need it 
        //var shared = PathManager()    // SHARED OBJECT IN QUESTION

        //Create AppModel instance.
        var mAppModel: AppModel? = null
    }

    //Comment this as will manage companion object.
    //var app: AppModel? = null

    fun setUp() {
        // Show loading...

        // Parse the JSON
        val gson = GsonBuilder().create()
        val text = mainActivity.resources.openRawResource(R.raw.jsonFile)  
            .bufferedReader().use { it.readText() }
        val appModel = gson.fromJson(text, AppModel::class.java)

        mAppModel = appModel

        performInitialPath()
    } 

    private fun performInitialPath() {

        val app = app?.let { it } ?: error("Attempted to start without an App Config.")

        mAppModel = app    // DEBUGGER SHOWS CORRECT VALUES HERE

        // Removed irrelevant code for readability, builds 'initialFoo' here

        this.mainActivity.addFragment(initialFoo)
    }
}

并在其他类中使用它

class Frag : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {

        var itemModels: List<ItemModel>? = null
        //Retrive the list from shared object.
        if(PathManager.mAppModel?.items != null) {  // NULL - WHY?
            itemModels = PathManager.mAppModel?.items  
        }
   }
}

回复于 2024-05-02T12:23:57+08:00

引用时，Kotlin Companion Object为null

1 回答

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