Debugging Tips and Tricks

Mobile development and 0:00 Xamarin are both evolving, which means not everything will always run smoothly. 0:01 So it's a good idea to know where to look when things go wrong. 0:07 There are a few new output logs that you should be aware of. 0:12 The Xamarin output log will tell you how your connection 0:16 with your Mac Agent is working. 0:20 It'll start connecting as soon as you load an iOS project. 0:22 So this is where you go to see what may have gone wrong, usually, 0:28 network-related issues. 0:32 Xamarin diagnostic output dialog shows the status of the ADB server, which is part of 0:35 Android SDK, which manages installing and running Android devices and emulators. 0:40 I'm not sure why it didn't call these outputs, Xamarin iOS and Xamarin Android. 0:47 The build output always has a lot of good information. 0:52 And especially with Xamarin because it's running so many customized build steps. 0:56 In the Tools, Option menu, Under Projects and 1:01 Solutions, select Build and Run, and change the MSBuild output 1:08 verbocity to something higher than usually is by default. 1:13 This will take the build extra time to run, so 1:19 turn it back down when you don't need it. 1:22 If you're dealing with runtime issues, the Debug output is your first place to look. 1:34 If you're having trouble with a physical device, the Device Log works 1:41 with Android or iOS devices that are connected to your computer. 1:46 A more powerful tool for Android diagnostics is the Android Device Monitor 1:51 which is an external app that comes with Android SDK. 1:56 You can find it in the Tools, Android menu. 1:59 The device monitor will let you inspect memory usage, 2:03 network status, file system, and much more. 2:07 You can see here the Android Device Monitor is monitoring the current 2:11 emulator. 2:16 When diagnosing an iOS runtime issue, you can use the Device Log. 2:21 But Xcode has more powerful diagnostic tools. 2:30 There's a developer tool called Instruments within Xcode which can 2:34 monitor memory usage, file activity, and much more. 2:38 This is only a few of the tools that you can use to debug Xamarin in 2:45 a Visual Studio environment. 2:49 There are some good resources in the Xamarin documentation 2:52 around troubleshooting errors with builds. 2:55 Check the teachers notes for links to the documentation. 2:58 Since we've gone over some build and 3:03 runtime troubleshooting, we can talk about handling exceptions. 3:04 Neither Android or iOS will deal with unhandled exceptions well. 3:09 If our app has an unhandled exception, your app will simply crash. 3:13 We've all seen this happen with our favorite app, but it's annoying and 3:17 can leave your app in a bad state. 3:22 Xamarin has normalized both Android and iOS exception handling and 3:24 has included an event to handle unhandled exceptions. 3:28 You can register a method to the AppDomain.CurrentDomain.UnhandledException 3:32 event, and trap an unhandled exception. 3:38 So any app you develop should at least handle this event. 3:41 In iOS, it should be registered in the AppDelegate class 3:46 in overridden FinishedLaunching method. 3:49 Here in the FinishedLauching method, 3:53 we'll register a handler for unhandled exceptions. 3:55 Using the System.AppDomain, 3:59 The CurrentDomain, We can handle the UnhandledException. 4:08 We simply do a System.Console.WriteLine which should show up in our debug logs. 4:33 So if we do something silly like in the middle of our 4:53 application throw new Exception, 4:58 When we run the iOS version of the app, On 5:10 our simulator, And we watch the debug output, 5:15 We can see our exception getting thrown. 5:30 And you can see our unhandled exception message. 5:44 Let's remove that. 5:51 Now, look at the Android version. 5:54 For Android, we use the same class to get to the unhandled exception. 5:56 And we'll write right out to the console again, Using WriteLine. 6:32 And we use the correct stream formatter, so that we can see who the sender is. 6:53 To make Android crash, let's throw an exception in the calculate click event. 7:06 Then switch to the Android project as our startup project, and debug. 7:16 Now, with the Android app, let's go ahead and add a number, although we know 7:23 it's gonna crash when I hit the Calculate button, and let's watch it. 7:28 An exception is thrown here, And we continue when the app crashes. 7:35 We scroll through the debug log and here is our unhandled exception message which 7:46 only shows up after we've stopped debugging. 7:51 So again, let's remove the exception. 7:55 There are some exceptions that are thrown that will not be caught by the unhandled 7:58 exception of it, like exceptions not thrown on the main thread and 8:02 unhandled objective C exceptions. 8:08 The teacher's notes includes a link to object C exceptions where this can happen. 8:12