在 MVVM Android 中显示对话框仅当 ViewModel 中的某些变量发生变化时才会抛出异常
Showing dialog in MVVM Android throws exception only when certain variable changes in the ViewModel
我有一个 MainActivity 使用 DrawerLayout 和带有 2 个片段的选项卡。
我的第一个片段包含 RecyclerView 中的元素列表，我可以单击每个元素以“select”它（调用 SDK 函数来登录硬件设备）。当 selected 时，这会触发 Fragment 的 ViewModel 的变化：
// 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
然后我在两个片段之间有一个共享的 ViewModel，它还有一个 currentDevice 变量，如下所示：
private val _currentDevice = MutableLiveData<ConnectedDevice>()
val currentDevice: LiveData<ConnectedDevice> by this::_currentDevice
所以在包含列表的片段中，我有以下代码来更新共享的 ViewModel 变量：
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()
}
})
}
问题是，如果设置了共享 ViewModel 的 currentDevice 变量，每当我尝试打开对话框或启动新的 activity 时，我都会遇到异常。如果我修改共享 ViewModel 中的 setCurrentDevice 函数，那么它工作正常（或者如果我不 select 任何设备）。
我在开始新的 Activity 时看到的异常是这样的：
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)
如果我尝试打开一个对话框，这就是：
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.onClick(DeviceManagementFragment.kt:52)
at android.view.View.performClick(View.java:7448)
at android.view.View.performClickInternal(View.java:7425)
at android.view.View.access00(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)
编辑：看起来问题实际上出在另一个片段上，我有以下代码（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()
}
})
如果我注释掉第二部分（出现 fetchChannels 的地方），效果很好。即使我只注释掉 fetchChannels 调用，它仍然有效。
这是fetchChannels函数的代码：
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]
}
}
}
下面一行给我带来了麻烦：
val fetchedChannels = deviceLibManager.getChannels(it.videoDevice)
那个函数就是这个：
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中的实现是这样的：
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()
}
}
其他函数只是进行网络调用并检索一些数据，根本不应该与 UI 混淆。
我正在用 Android 10.
的小米 Mi A3 进行测试
有人可以帮助我吗？谢谢。
所以我真的不知道为什么，但我找到了答案。
在SDK中，函数getZeroChannel和getAllChannels虽然进行了网络调用，但并没有挂起函数。所以我所做的是：
将withContext(Dispatchers.IO)部分移动到那两个函数（实际进行网络调用的函数），并使它们挂起函数。
从 getChannelsAsync 函数中删除 withContext(Dispatchers.IO) 部分。不过，请将其保留为暂停功能。
进行这些更改后，一切正常。我仍然不知道为什么，所以如果有人能透露一些信息，那将不胜感激。
我有一个 MainActivity 使用 DrawerLayout 和带有 2 个片段的选项卡。
我的第一个片段包含 RecyclerView 中的元素列表，我可以单击每个元素以“select”它（调用 SDK 函数来登录硬件设备）。当 selected 时，这会触发 Fragment 的 ViewModel 的变化：
// 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
然后我在两个片段之间有一个共享的 ViewModel，它还有一个 currentDevice 变量，如下所示：
private val _currentDevice = MutableLiveData<ConnectedDevice>()
val currentDevice: LiveData<ConnectedDevice> by this::_currentDevice
所以在包含列表的片段中，我有以下代码来更新共享的 ViewModel 变量：
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()
}
})
}
问题是，如果设置了共享 ViewModel 的 currentDevice 变量，每当我尝试打开对话框或启动新的 activity 时，我都会遇到异常。如果我修改共享 ViewModel 中的 setCurrentDevice 函数，那么它工作正常（或者如果我不 select 任何设备）。
我在开始新的 Activity 时看到的异常是这样的：
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)
如果我尝试打开一个对话框，这就是：
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.onClick(DeviceManagementFragment.kt:52)
at android.view.View.performClick(View.java:7448)
at android.view.View.performClickInternal(View.java:7425)
at android.view.View.access00(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)
编辑：看起来问题实际上出在另一个片段上，我有以下代码（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()
}
})
如果我注释掉第二部分（出现 fetchChannels 的地方），效果很好。即使我只注释掉 fetchChannels 调用，它仍然有效。
这是fetchChannels函数的代码：
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]
}
}
}
下面一行给我带来了麻烦：
val fetchedChannels = deviceLibManager.getChannels(it.videoDevice)
那个函数就是这个：
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中的实现是这样的：
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()
}
}
其他函数只是进行网络调用并检索一些数据，根本不应该与 UI 混淆。
我正在用 Android 10.
的小米 Mi A3 进行测试有人可以帮助我吗？谢谢。
所以我真的不知道为什么，但我找到了答案。
在SDK中，函数getZeroChannel和getAllChannels虽然进行了网络调用，但并没有挂起函数。所以我所做的是：
将
withContext(Dispatchers.IO)部分移动到那两个函数（实际进行网络调用的函数），并使它们挂起函数。从
getChannelsAsync函数中删除withContext(Dispatchers.IO)部分。不过，请将其保留为暂停功能。
进行这些更改后，一切正常。我仍然不知道为什么，所以如果有人能透露一些信息，那将不胜感激。