僅當ViewModel中的某些變數更改時，在MVVMAndroid中顯示對話框才會引發例外-有解無憂

我有一個 MainActivity 使用 DrawerLayout 和帶有 2 個片段的選項卡。

我的第一個片段包含 RecyclerView 中的元素串列，我可以單擊每個元素以“選擇”它（它呼叫 SDK 函式以登錄到硬體設備）。選中后，這會觸發 Fragment 的 ViewModel 的更改：

// Selected device changes when an item is clicked
private val _devices = MutableLiveData<List<DeviceListItemViewModel>>()
private val _selectedDevice = MutableLiveData<ConnectedDevice>()
val devices: LiveData<List<DeviceListItemViewModel>> by this::_devices
val selectedDevice: LiveData<ConnectedDevice> by this::_selectedDevice

然后我在兩個片段之間有一個共享的 ViewModel，它也有一個currentDevice像這樣的變數：

private val _currentDevice = MutableLiveData<ConnectedDevice>()
val currentDevice: LiveData<ConnectedDevice> by this::_currentDevice

所以在包含串列的 Fragment 中，我有以下代碼來更新共享的 ViewModel 變數：

private val mViewModel: DeviceManagementViewModel by viewModels()
private val mSharedViewModel: MainActivityViewModel by activityViewModels()

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        Log.d(classTag, "Fragment view created")
        val binding = ActivityMainDevicesManagementFragmentBinding.bind(view)
        binding.apply {
            viewModel = mViewModel
            lifecycleOwner = viewLifecycleOwner
        }

        // Observe fragment ViewModel
        // If any device is clicked on the list, do the login on the shared ViewModel
        mViewModel.selectedDevice.observe(this, {
            mSharedViewModel.viewModelScope.launch {
                if (it != null) {
                    mSharedViewModel.setCurrentDevice(videoDevice = it)
                } else mSharedViewModel.unsetCurrentDevice()
            }
        })
    }

問題是，如果設定了共享 ViewModel 的currentDevice變數，則每當我嘗試打開 Dialog 或啟動新活動時都會遇到例外。如果我修改共享 ViewModel 中的 setCurrentDevice 函式，則它可以正常作業（或者如果我不選擇任何設備）。

啟動新活動時，我看到的例外情況是：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.placeholder.easyview/com.example.myapp.activities.settings.SettingsActivity}: java.lang.IllegalArgumentException: display must not be null
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3430)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3594)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2067)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7698)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:952)
     Caused by: java.lang.IllegalArgumentException: display must not be null
        at android.app.ContextImpl.createDisplayContext(ContextImpl.java:2386)
        at android.content.ContextWrapper.createDisplayContext(ContextWrapper.java:977)
        at com.android.internal.policy.DecorContext.<init>(DecorContext.java:50)
        at com.android.internal.policy.PhoneWindow.generateDecor(PhoneWindow.java:2348)
        at com.android.internal.policy.PhoneWindow.installDecor(PhoneWindow.java:2683)
        at com.android.internal.policy.PhoneWindow.getDecorView(PhoneWindow.java:2116)
        at androidx.appcompat.app.AppCompatActivity.initViewTreeOwners(AppCompatActivity.java:219)
        at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:194)
        at com.example.myapp.activities.settings.SettingsActivity.onCreate(SettingsActivity.kt:34)
        at android.app.Activity.performCreate(Activity.java:8000)
        at android.app.Activity.performCreate(Activity.java:7984)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1310)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3403)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3594) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2067) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7698) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:952)

如果我嘗試打開對話框，則會出現這種情況：

java.lang.ArrayIndexOutOfBoundsException: length=16; index=2448
        at android.view.InsetsState.peekSource(InsetsState.java:374)
        at android.view.InsetsSourceConsumer.updateSource(InsetsSourceConsumer.java:291)
        at android.view.InsetsController.updateState(InsetsController.java:654)
        at android.view.InsetsController.onStateChanged(InsetsController.java:621)
        at android.view.ViewRootImpl.setView(ViewRootImpl.java:1058)
        at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:409)
        at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:110)
        at android.app.Dialog.show(Dialog.java:340)
        at android.app.AlertDialog$Builder.show(AlertDialog.java:1131)
        at com.example.myapp.activities.main.fragments.DeviceManagementFragment.showAddDeviceMethodDialog(DeviceManagementFragment.kt:151)
        at com.example.myapp.activities.main.fragments.DeviceManagementFragment.access$showAddDeviceMethodDialog(DeviceManagementFragment.kt:33)
        at com.example.myapp.activities.main.fragments.DeviceManagementFragment$onViewCreated$$inlined$apply$lambda$1.onClick(DeviceManagementFragment.kt:52)
        at android.view.View.performClick(View.java:7448)
        at android.view.View.performClickInternal(View.java:7425)
        at android.view.View.access$3600(View.java:810)
        at android.view.View$PerformClick.run(View.java:28309)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7698)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:952)

編輯：看起來問題實際上出在另一個片段中，在那里我有以下代碼（在onViewCreated方法中）：

// If the shared view model device changes, this must change too
        mSharedViewModel.currentDevice.observe(this, {
            if (it != null) {
                mViewModel.setCurrentDevice(it)
            } else mViewModel.unsetCurrentDevice()
        })

        
        mViewModel.currentDevice.observe(this, {
            if (it != null) {
                mViewModel.fetchChannels()
            }
        })

如果我注釋掉第二部分（fetchChannels發生的地方），它運行良好。即使我只注釋掉fetchChannels呼叫，它也能作業。

這是fetchChannels函式的代碼：

fun fetchChannels() = viewModelScope.launch {
        Log.d(classTag, "Getting channels for device ${currentDevice.value}")
        currentDevice.value?.let {
            val fetchedChannels = deviceLibManager.getChannels(it.videoDevice)
            _currentDevice.value?.channels?.clear()
            _currentDevice.value?.channels?.addAll(fetchedChannels)
            if (fetchedChannels.isNotEmpty()) {
                _currentDevice.value?.currentChannel = fetchedChannels[0]
            }
        }
    }

下面這行給我帶來了麻煩：

val fetchedChannels = deviceLibManager.getChannels(it.videoDevice)

該功能就是這樣：

suspend fun getChannels(videoDevice: VideoDevice): List<VideoChannel> {
        try {
            Log.i(classTag, "Getting channels from device ${videoDevice}")
            val channels = videoDevice.getChannelsAsync()
            return channels
        } catch (exception: Exception) {
            when (exception) {
                is UnknownVendorException -> {
                    Log.w(classTag, "Device ${videoDevice} cannot get channels because the vendor is unknown")
                }
                is NetworkException -> {
                    Log.w(classTag, "Device ${videoDevice} cannot get channels because it is unreachable")
                }
                else -> {
                    Log.w(classTag, "Device ${videoDevice} cannot get channels, reason: ${exception.message}")
                }
            }
            return emptyList()
        }
    }

SDK 中的實作是這樣的：

override suspend fun getChannelsAsync(): List<VideoChannel> = withContext(Dispatchers.IO) {
        Log.i(classTag, "Trying to get channels for device: $logName")
        val channels = ArrayList<VideoChannel>()
        getZeroChannel()?.let {
            channels.add(it)
        }
        channels.addAll(getAllChannels())
        if (channels.isNotEmpty()) {
            Log.i(classTag, "Successfully retrieved ${channels.size} channels for device: $logName")
            return@withContext channels
        } else {
            Log.w(classTag, "Error retrieving channels for device $logName or no channels exist")
            throw Exception()
        }
    }

其他函式只是進行網路呼叫并檢索一些資料，它根本不應該與 UI 混淆。

我正在使用 Android 10 使用小米 Mi A3 進行測驗。

有人能幫我嗎？謝謝你。

uj5u.com熱心網友回復：

所以我真的不知道為什么，但我找到了答案。

在 SDK 中，函式getZeroChannel和getAllChannels不是掛起函式，盡管它們進行網路呼叫。所以我所做的是：

將withContext(Dispatchers.IO)部分移至這兩個函式（實際進行網路呼叫的函式），并使它們掛起函式。
withContext(Dispatchers.IO)從getChannelsAsync功能中洗掉該部件。將其保留為掛起功能。

在這些更改之后，一切都按預期作業。我仍然不知道為什么，所以如果有人能解釋一下，那將是非常感激的。

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標籤：安卓 android-fragments 虚拟机 android-alertdialog android-数据绑定

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