Communicating between a UIView object and a ViewController object in an iPhone App

Introduction

As mobile app development continues to evolve, the need for seamless communication between different components of an application becomes increasingly important. In this article, we will explore how to achieve this communication between a UIView object (SliderView) and a ViewController object.

Background

In iOS development, a UIViewController is typically responsible for managing its view hierarchy, handling user input, and updating the app’s UI state. On the other hand, UIView objects are used to create custom views that can be added to a UIViewController. In our case, we have a SliderView subclass of UIView that we want to communicate with our ViewController.

The Problem

In our example application, we have a UIScrollView in the Storyboard that has a SliderView inside it. We want to disable the bouncy vertical scrolling of the UIScrollView when the user touches the SliderView. However, simply setting self.scrollView.bounces = NO in our ViewController does not achieve this, as we are only enabling this behavior for a specific view controller lifecycle method (viewDidLoad). Instead, we want to disable bouncy scrolling specifically when a certain action occurs (e.g., touches began) within the SliderView.

Solution: Using Delegates

To solve this problem, we will use delegates. A delegate is an object that receives notifications from another object, often used for communication between objects in different parts of an application.

Creating a Delegate Protocol

First, let’s create a delegate protocol (SliderViewDelegate) for our SliderView class:

// SliderView.h

@protocol SliderViewDelegate <NSObject>
@optional
- (void)isScrollViewToBounce:(BOOL)isBounce;
@end

This protocol defines a single method (isScrollViewToBounce:), which will be called when the user interacts with our SliderView.

Modifying SliderView Class

Next, we need to modify our SliderView class to implement this delegate protocol. We also need to create a property for our delegate:

// SliderView.m

#import "SliderViewDelegate.h"

@interface SliderView : UIView <SliderViewDelegate>
@property (nonatomic, weak) id<SliderViewDelegate> sliderViewDelegate;

We will use this property to hold a reference to the object that implements our SliderViewDelegate protocol.

Implementing Delegate Methods

In our SliderView class, we need to implement the delegate methods specified in the protocol. These methods will be called when the user interacts with our SliderView. In this case, we want to call these methods from within our touchesBegan: method:

// SliderView.m

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    [self.sliderViewDelegate isScrollViewToBounce:NO];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [self.sliderViewDelegate isScrollViewToBounce:YES];
}

In these methods, we simply call the isScrollViewToBounce: method on our delegate object.

Enabling Delegation

We also need to enable delegation from within our ViewController. We can do this by:

// ViewController.m

#import "SliderView.h"

@interface ViewController () <SliderViewDelegate>
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    self.sliderView = (SliderView *)self.scrollView.subviews.firstObject;
    self.sliderView.setSliderViewDelegate:self];
}

Here, we retrieve the SliderView object from our UIScrollView, create a reference to it as our delegate, and set it as our delegate.

Creating Delegate Method in ViewController

Now that we have enabled delegation, we need to implement our delegate method (isScrollViewToBounce:) within our ViewController. This method will update the bouncy scrolling behavior of our UIScrollView:

// ViewController.m

- (void)isScrollViewToBounce:(BOOL)isBounce {
    self.scrollView.bounces = isBounce;
}

This method simply sets self.scrollView.bounces to the specified value.

Removing Delegation

Finally, we need to remove delegation from within our ViewController. We can do this by releasing the delegate reference in our dealloc method:

// ViewController.m

#pragma mark Memory management methods

- (void)dealloc {
    [selfscrollView setSliderViewDelegate:nil];
}

This ensures that our delegate object is properly released when it is no longer needed.

Conclusion

In this article, we have explored how to communicate between a UIView object (SliderView) and a ViewController object. We used delegates to achieve this communication, which allowed us to pass notifications from the SliderView to our ViewController. This solution provides a flexible way to handle user input and update the app’s UI state in a more modular and maintainable way.

Additional Considerations

When working with delegates in iOS development, there are several other things to consider:

• Null Safety: Be aware that delegate methods may be called on a null reference. To mitigate this risk, always check for nil before calling a delegate method.
• Weak References: When creating weak references to delegate objects, make sure you properly release any retained relationships to prevent memory leaks.
• Delegate Cycles: Be cautious of delegate cycles where two or more objects have strong references to each other. These can lead to unexpected behavior and crashes.

By following these best practices and using delegates effectively in your iOS development projects, you can create more robust, scalable, and maintainable applications that better handle user input and complex interactions.

Last modified on 2023-09-25