How can I use BaseViewModel classes for shared error handling in MvvmCross

1. Creating a BaseViewModel**

First, you need to create a BaseViewModel class that will contain the shared error handling logic. This class should inherit from `MvxViewModel` to leverage MvvmCross's features.

csharp
public class BaseViewModel : MvxViewModel
{
    // Shared error handling logic goes here
}

2. Implementing Error Handling Logic**

In the BaseViewModel, you can define methods for handling errors. For example, you might create a method to handle exceptions during asynchronous operations:

csharp
protected void HandleException(Exception ex)
{
    // Handle the exception here, e.g., log it, display an error message, etc.
    // You can use MvxMessenger to notify other parts of the app about the error.
}

3. Using MvxNotifyTask for Async Operations**

MvvmCross provides MvxNotifyTask, which is useful for handling asynchronous operations and exceptions. You can use it to wrap your async methods and handle exceptions gracefully:

csharp
private MvxNotifyTask _myTaskNotifier;

public MvxNotifyTask MyTaskNotifier
{
    get => _myTaskNotifier;
    private set => SetProperty(ref _myTaskNotifier, value);
}

public void MyCommandExecute()
{
    MyTaskNotifier = MvxNotifyTask.Create(() => MyMethodAsync(), onException: HandleException);
}

private async Task MyMethodAsync()
{
    // Your async operation here
}

private void HandleException(Exception ex)
{
    // Handle the exception
}

4. Inheriting from BaseViewModel**

Now, have your specific view models inherit from the BaseViewModel. This allows them to use the shared error handling logic:

csharp
public class MyViewModel : BaseViewModel
{
    // Use the error handling methods from BaseViewModel here
}

5. Displaying Errors**

To display errors, you can use platform-specific UI elements like `UIAlertViews` on iOS, `Toasts` on Android, or `MessageBoxes` on Windows platforms. You might also use MvxMessenger to notify other parts of your app about errors and handle them accordingly:

csharp
// In BaseViewModel or a separate error handler class
public void DisplayError(string message)
{
    // Use MvxMessenger to notify other parts of the app
    // or directly display the error using platform-specific code
}

6. Using an App-Level Error Router**

For a more centralized approach, you can implement an app-level "error router" that catches errors from view models and routes them to the appropriate UI components for display. This can be achieved using interfaces like IErrorSource or IErrorReporter, which are initialized as singletons and subscribed to by platform-specific UI components[1][4].

Conclusion

By using a BaseViewModel for shared error handling in MvvmCross, you can efficiently manage error handling across your application. This approach allows for centralized logic that can be easily extended or modified as needed. Combining this with MvvmCross features like MvxNotifyTask and MvxMessenger provides a robust error handling system.