我有一个Xamarin跨平台应用程序，它在iOS端使用bluetooth-central后台模式来保持与蓝牙到串行加密狗的连接。一切都很好，除了我正在尝试实现CBCentralManagerDelegate.WillRestoreState方法(有关详细信息，请参阅iOS文档和无用的Xamarin文档)。
从iOS文档中，我可以看到第二个参数有一个元素，它包含CBCentralManager.RestoredStatePeripheralsKey中恢复的外围设备，并且该元素是CBPeripherals的NSArray。因此，我在类中编写了这个方法，它覆盖CBCentralManagerDelegate:
// Handle state restoration if OS restores CoreBluetooth peripherals
public override void WillRestoreState(CBCentralManager central, NSDictionary state)
{
NSObject restoredPeripherals = new NSObject();
if (state.TryGetValue(CBCentralManager.RestoredStatePeripheralsKey, out restoredPeripherals))
{
Logger.Debug("Restoring CoreBluetooth Peripherals...");
NSArray<CBPeripheral> peripherals = restoredPeripherals as NSArray<CBPeripheral>;
foreach (CBPeripheral peripheral in peripherals)
{
Logger.Debug("Loading preexisting peripherals");
discoveredPeripherals.Add(peripheral.Name, peripheral);
}
}
base.WillRestoreState(central, state);
}
问题出在这样一行：NSArray<CBPeripheral> peripherals = restoredPeripherals as NSArray<CBPeripheral>;
这条线会导致撞车事故。在极少数情况下，我能够在调试器中捕捉到这一点(在复制这一点时很难保持调试器的连接)，它表明这一行是无效的强制转换。
这是我从iPad上得到的日志：
Nov 15 14:22:58 iPad-Mini Warning 520 MyApp [Debug] Restoring CoreBluetooth Peripherals... (
Nov 15 14:22:58 iPad-Mini Warning 520 MyApp
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 15 MyApp 0x00083733 -[Messenger_iOS_TruConnectBLEFactory_ManagerDelegate centralManager:willRestoreState:] + 60
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical:
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 21 libdispatch.dylib 0x20df3b93 <redacted> + 182
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 13 libmonosgen-2.0.dylib 0x08d4ff6b mono_runtime_invoke + 138
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 4 libxamarin-debug.dylib 0x08fa2360 xamarin_printf + 0
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 24 libsystem_pthread.dylib 0x20fadb29 _pthread_wqthread + 1024
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 1 libsystem_platform.dylib 0x20faa077 _sigtramp + 42
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 2 libsystem_pthread.dylib 0x20fb0733 pthread_kill + 62
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 19 libdispatch.dylib 0x20df6423 <redacted> + 1758
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 8 libmonosgen-2.0.dylib 0x08cde29f handle_signal_exception + 42
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 12 libmonosgen-2.0.dylib 0x08d4ffd5 do_runtime_invoke + 78
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 14 MyApp 0x0008393b _ZL31native_to_managed_trampoline_55P11objc_objectP13objc_selectorPP11_MonoMethodP16CBCentralManagerP12NSDictionaryj + 516
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 16 CoreBluetooth 0x2637abe3 <redacted> + 2486
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical:
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 22 libdispatch.dylib 0x20df85e9 <redacted> + 1560
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 9 ??? 0x00000000 0x0 + 0
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 6 libmonosgen-2.0.dylib 0x08ce6235 mono_handle_exception_internal + 3162
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 11 libmonosgen-2.0.dylib 0x08cf10f5 mono_jit_runtime_invoke + 712
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp Unhandled managed exception:
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 25 libsystem_pthread.dylib 0x20fad718 start_wqthread + 8
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 7 libmonosgen-2.0.dylib 0x08ce55d7 mono_handle_exception + 30
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 5 libmonosgen-2.0.dylib 0x08d1d7cd mono_invoke_unhandled_exception_hook + 100
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 18 libdispatch.dylib 0x20de9823 <redacted> + 10
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 3 libsystem_c.dylib 0x20e9b0ad abort + 108
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 17 CoreBluetooth 0x263869f3 <redacted> + 62
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 10 libmscorlib.dll.dylib 0x00d49520 wrapper_runtime_invoke_object_runtime_invoke_dynamic_intptr_intptr_intptr_intptr + 256
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 0 libmonosgen-2.0.dylib 0x08ce6637 mono_handle_native_crash + 196
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: Stacktrace:
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 23 libdispatch.dylib 0x20df7fcd <redacted> + 96
Nov 15 14:22:59 iPad-Mini Warning 520 MyApp critical: 20 libdispatch.dylib 0x20df5a61 <redacted> + 284
有人知道为什么会崩溃吗？此外，如果有人有用Xamarin实现这种方法的例子，请分享链接。我找不到(
我想应该转换为NSArray而不是NSArray<CBPeripheral>。
尝试以下操作：
NSArray peripherals = (NSArray) restoredPeripherals;
for (nuint i = 0; i < peripherals.Count; i++)
{
CBPeripheral peripheral = peripherals.GetItem<CBPeripheral>(i);
Logger.Debug("Loading preexisting peripherals");
discoveredPeripherals.Add(peripheral.Name, peripheral);
}