How do I create a custom MvxPresentationHint in MvvmCross

Step 1: Create a Custom Hint Class

First, you need to create a subclass of `MvxPresentationHint`. This class will define the type of presentation hint you want to use. You can add properties to this class if you need to pass additional information with the hint.

csharp
public class MyCustomHint : MvxPresentationHint
{
    public string ImportantInformation { get; set; }

    public MyCustomHint(string importantInformation)
    {
        ImportantInformation = importantInformation;
    }
}

Step 2: Register the Hint Handler

Next, you need to register a handler for your custom hint. This is done in the platform-specific setup class by overriding the `CreateViewPresenter` method. You will add a handler using the `AddPresentationHintHandler` method of the view presenter.

For example, on iOS, you would do something like this:

csharp
protected override IMvxIosViewPresenter CreateViewPresenter()
{
    var presenter = base.CreateViewPresenter();
    presenter.AddPresentationHintHandler(hint => HandleMyCustomHint(hint));
    return presenter;
}

You would need to implement the `HandleMyCustomHint` method:

csharp
private async Task HandleMyCustomHint(MyCustomHint hint)
{
    bool result = false;
    if (hint.ImportantInformation != null)
    {
        // Handle the presentation change here
        result = true;
    }
    return result;
}

Step 3: Trigger the Presentation Change

Finally, you need to trigger the presentation change by calling the `ChangePresentation` method from your view model or wherever you need to initiate the change. This method is typically accessed through the `IMvxNavigationService`.

csharp
private async Task MyMethodAsync()
{
    // Your code here
    bool handled = await mvxNavigationService.ChangePresentation(new MyCustomHint("example"));
    // Your code here
}

Platform-Specific Considerations

While the steps above are generally applicable across platforms, you need to ensure that you implement the hint handling in each platform's setup class. For example, if you're working with UWP, you would override `CreateViewPresenter` in the UWP setup class and register the handler there.

csharp
protected override IMvxWindowsViewPresenter CreateViewPresenter(IMvxWindowsFrame rootFrame)
{
    var presenter = base.CreateViewPresenter(rootFrame);
    presenter.AddPresentationHintHandler(hint => HandleMyCustomHint(hint));
    return presenter;
}

This way, you can ensure that your custom presentation hints are handled correctly across all platforms supported by your application.

Conclusion

Creating a custom `MvxPresentationHint` allows you to extend the presentation capabilities of MvvmCross, enabling you to handle complex navigation scenarios or custom view presentations. By following these steps, you can integrate custom presentation logic into your cross-platform applications.