android - 如何使用LiveData在ViewModel中启动Kotlin Coroutine

Question

我试图从ViewModel异步获取所有可启动的已安装应用程序。
这是我的ViewModel类的样子:

class AppInstalledViewModel(application: Application) : AndroidViewModel(application) {
    private var appInstalledLiveData: LiveData<ArrayList<AppInstalled>>? = null

    fun getAppInstalledLiveData(): LiveData<ArrayList<AppInstalled>> {
        if (appInstalledLiveData == null) {
            appInstalledLiveData = liveData {
                val appInstalled = ArrayList<AppInstalled>()
                val pm: PackageManager =
                    getApplication<Application>().applicationContext.packageManager

                val main = Intent(Intent.ACTION_MAIN, null).addCategory(Intent.CATEGORY_LAUNCHER)

                // Get launchable installed apps
                val launchAble = pm.queryIntentActivities(main, 0)

                // Sort the installed app list
                Collections.sort(launchAble, ResolveInfo.DisplayNameComparator(pm))

                // Iterate over each launchable app and
                // add it to AppInstalled ArrayList
                for (l in launchAble) {
                    val activityInfo = l.activityInfo

                    activityInfo.run {
                        appInstalled.add(
                            AppInstalled(
                                loadLabel(pm).toString(),
                                applicationInfo.packageName,
                                loadIcon(pm)
                            )
                        )
                    }
                }

                emit(appInstalled)
            }
        }
        return appInstalledLiveData as LiveData<ArrayList<AppInstalled>>
    }
}

加载应用列表没有问题。但是，似乎我的代码仍然不能异步运行，因为在进入应用程序已安装列表 Activity 之前，它仍然冻结了几秒钟。
这是我用来观察 LiveData的代码:

appInstalledViewModel.getAppInstalledLiveData().observe(this, Observer { appInstalledItem ->
    if (appInstalledItem.size > 0) {
        appInstalledAdapter.appInstalled.addAll(appInstalledItem)
        app_list_progressbar.visibility = View.GONE
    }
})

尝试在Android Development上使用Kotlin让我感到困惑。这是我第一次使用Kotlin开发应用程序。我什至不知道我上面编写的代码在Kotlin风格的背景下是否是一个好的代码。
请帮我!谢谢!

Answer 1

这是因为在Main调度程序中执行了长时间运行的作业。我强烈建议您看看Coroutines Dispatchers。
因此，如果将调度程序更改为Dispatchers.Default，从而导致获取已安装的应用程序在后台线程中执行，因此，UI将永远不会冻结。

appInstalledLiveData = liveData(Dispatchers.Default) {
    ...
}

更多:
如果要实现更好的结构，最好不通过调用函数来访问 LiveData:

class AppInstalledViewModel(application: Application) : AndroidViewModel(application) {

    private val reloadLiveData = MutableLiveData<Unit>()

    val installedAppsLiveData: LiveData<ArrayList<AppInstalled>> =
        reloadLiveData.switchMap {
            liveData(Dispatchers.Default) {
                emit(fetchInstalledApps())
            }
        }

    fun reloadApps() {
        reloadLiveData.postValue(Unit)
    }

    private fun fetchInstalledApps(): ArrayList<AppInstalled> {
        val appInstalled = ArrayList<AppInstalled>()
        val pm: PackageManager = getApplication<Application>().applicationContext.packageManager

        val main = Intent(Intent.ACTION_MAIN, null).addCategory(Intent.CATEGORY_LAUNCHER)

        // Get launchable installed apps
        val launchAble = pm.queryIntentActivities(main, 0)

        // Sort the installed app list
        Collections.sort(launchAble, ResolveInfo.DisplayNameComparator(pm))

        // Iterate over each launchable app and
        // add it to AppInstalled ArrayList
        for (l in launchAble) {
            val activityInfo = l.activityInfo

            activityInfo.run {
                appInstalled.add(
                    AppInstalled(
                        loadLabel(pm).toString(),
                        applicationInfo.packageName,
                        loadIcon(pm)
                    )
                )
            }
        }
        return appInstalled
    }
}

现在，在片段中:

appInstalledViewModel.installedAppsLiveData.observe(this, Observer { appInstalledItem ->
    if (appInstalledItem.size > 0) {
        appInstalledAdapter.appInstalled.addAll(appInstalledItem)
        app_list_progressbar.visibility = View.GONE
    }
})

appInstalledViewModel.reloadApps()

使用此结构，如果要刷新加载的数据，只需调用 appInstalledViewModel.reloadApps()即可，应用程序列表将得到更新。