我如何在片段中的 onViewCreated 之外延迟初始化属性未初始化的视图模型答案

【问题标题】：How i lateinit propert initialized viewModel outside onViewCreated in fragment我如何在片段中的 onViewCreated 之外延迟初始化属性未初始化的视图模型
【发布时间】：2020-06-10 21:00:37
【问题描述】：

我尝试在导航视图中单击按钮并在电影片段中过滤电影

我需要调整mainactivity中的filterButton并在MoviesFragment().filtMovie中获取数据

主活动；

val navRight : NavigationView = findViewById(R.id.nav_right)
        (navRight.menu.findItem(R.id.filtBut).actionView as Button).run {
            this.setOnClickListener {
                MoviesFragment().filterMovie(filtQuality,filtGenre,filtRate,filtYear,filtLang)
            }
        }

和电影片段；

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        activity?.setTitle(R.string.movies)

        viewModel = ViewModelProviders.of(this).get(MoviesViewModel::class.java)
        viewModel.refreshData(sortMethod)

        movieList.layoutManager = LinearLayoutManager(context)
        movieList.adapter = movieAdapter

        swipeRefreshLayout.setOnRefreshListener {
            movieList.visibility = View.GONE
            movieError.visibility = View.GONE
            movieLoading.visibility = View.GONE
            viewModel.refreshData(sortMethod)
            swipeRefreshLayout.isRefreshing = false
        }
}

fun filterMovie(quality : String, genre : String, rate : String, year : String, lang : String){

        viewModel.filterMovie(quality, genre, rate, year, lang)

    }

还有我的logcat；

2020-06-10 23:29:46.474 18721-18721/com.enesseval.moviedeneme E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.enesseval.moviedeneme, PID: 18721
    kotlin.UninitializedPropertyAccessException: lateinit property viewModel has not been initialized
        at com.enesseval.moviedeneme.view.MoviesFragment.filterMovie(MoviesFragment.kt:110)
        at com.enesseval.moviedeneme.view.MainActivity$onCreate$$inlined$run$lambda$6.onClick(MainActivity.kt:87)
        at android.view.View.performClick(View.java:7125)
        at android.view.View.performClickInternal(View.java:7102)
        at android.view.View.access$3500(View.java:801)
        at android.view.View$PerformClick.run(View.java:27336)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
2020-06-10 23:29:46.488 18721-18721/com.enesseval.moviedeneme I/Process: Sending signal. PID: 18721 SIG: 9

【问题讨论】：

标签： android-fragments kotlin mvvm android-viewmodel

【解决方案1】：

行内：

this.setOnClickListener {
           MoviesFragment().filterMovie(filtQuality,filtGenre,filtRate,filtYear,filtLang)
}

您创建了新的MoviesFragment 实例。但是onViewCreated 没有调用，因为这个新的片段实例没有添加到后台堆栈并且没有显示。这就是为什么视图模型没有初始化并且你得到异常的原因。

你应该在fragment backstack中找到现有的fragment，并在上面调用filterMovie。

get the latest fragment in backstack

Get fragment from backstack

【讨论】：