Understanding the Problem: Why Can’t I Tap Input Elements After Resizing a Scroll View?

As mobile app developers, we have all encountered situations where we need to handle complex user interfaces, including scroll views and keyboard resizing. In this article, we will delve into the intricacies of how scroll views interact with input elements and explore the solution to a common issue that can arise when resizing a scroll view.

Background: Understanding Scroll Views and Keyboard Resizing

A scroll view is a UI component that allows users to interact with content that exceeds the screen’s height or width. When a keyboard appears, we need to resize the scroll view accordingly to ensure that all content remains accessible. This process involves calculating the new height of the scroll view based on the keyboard’s metrics.

In iOS, the UIScrollView class provides an interface for working with scroll views. By default, it uses an autosizing mask to determine how its content should be laid out within its bounds. When we resize the scroll view using a notification, the autosizingMask property is set to UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth, which allows the content to adapt to changes in the scroll view’s size.

However, when we resize the scroll view after it has been focused on an input element (e.g., text field), some unexpected behavior may occur. Specifically, tapping on other elements within the scroll view can become difficult or even impossible due to a layer that seems to cover those elements.

Identifying the Root Cause: Autosizing Masks and View Layout

To understand why this issue arises, let’s examine how autosizing masks work in iOS. When we set an autosizing mask on a view, it determines how the view should be laid out within its bounds based on the constraints provided by its superview.

In our example, when we resize the scroll view using the notification, we are setting its autosizingMask property to UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth. This tells the scroll view to adapt to changes in its height and width, ensuring that all content remains accessible.

However, when we focus on an input element within the scroll view, the input element’s frame is updated to accommodate the keyboard. Unfortunately, this can cause the autosizing mask of the scroll view’s subview (i.e., the text field) to become invalid. As a result, the subview’s layout is not properly recalculated, leading to unexpected behavior.

The Fix: Disabling Autosizing Masks

To resolve this issue, we need to disable the autosizing mask on the input element’s subview when it becomes focused on an input element within the scroll view. This can be achieved by commenting out or modifying the line of code that sets the autosizingMask property.

// self.subView.autoresizingMask = (UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth);

By disabling the autosizing mask, we allow the subview’s layout to be properly recalculated when it becomes focused on an input element. This ensures that all content within the scroll view remains accessible and responsive to user interactions.

Additional Considerations: Optimizations and Best Practices

While disabling the autosizing mask is a viable solution to this issue, there are additional considerations we can take into account to optimize our code and improve overall performance.

Using Auto Layout for Input Elements

One alternative approach is to use Auto Layout to position input elements within the scroll view. By defining constraints on the input element’s frame, we can ensure that it remains properly positioned even when the scroll view is resized or focused on an input element.

For example:

// Create a constraint to pin the top of the text field to the bottom of its superview
self.textField.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
    self.textField.topAnchor.constraint(equalTo: self.scrollView.bottomAnchor),
    // ...
])

By using Auto Layout, we can avoid setting an invalid autosizing mask and ensure that our input elements remain properly positioned within the scroll view.

Conclusion

In this article, we explored a common issue that can arise when resizing a scroll view and focusing on an input element. By understanding how autosizing masks work in iOS and disabling them when necessary, we can resolve this issue and ensure that all content within the scroll view remains accessible and responsive to user interactions.

We also discussed additional considerations for optimizing our code and improving overall performance, including using Auto Layout to position input elements. By taking these best practices into account, we can create more robust, scalable, and maintainable iOS applications.

Last modified on 2023-06-20