UIView Tutorial for iOS: How To Make a Custom UIView in iOS 5: A 5 Star Rating View

L'Escapadou took all the stars, so I was just left with this Kermit :)

L'Escapadou took all the stars, so I was just left with this Kermit :)

Update 2/17/12: Fully updated for iOS 5.

In an update I have planned for one of my apps, I had a need to develop a 5-star rating view so people could rate items they make with the app.

As I was working on this control, I thought this might make a good UIView tutorial – especially since it would fit in well with our previous tutorial on how to rate babes with Facebook ;]

So in this UIView tutorial, we’ll go through a short example of making a 5-star rating control and in the process we’ll learn the ropes of creating custom UIViews in general.

Diving In

Let’s dive right in by creating a new project with the iOS\Application\Single View Application template and name it CustomView. Make sure the Device Family is set to iPhone, Use Storyboard and Use Automatic Reference Counting are checked, and click Next.

Now create a new file with the iOS\Cocoa Touch\Objective C class template. Enter RateView for the Class name, and UIView for Subclass of.

Next, let’s fill in our header file. Replace the contents of RateView.h with the following:

#import <UIKit/UIKit.h>

@class RateView;

@protocol RateViewDelegate
- (void)rateView:(RateView *)rateView ratingDidChange:(float)rating;
@end

@interface RateView : UIView

@property (strong, nonatomic) UIImage *notSelectedImage;
@property (strong, nonatomic) UIImage *halfSelectedImage;
@property (strong, nonatomic) UIImage *fullSelectedImage;
@property (assign, nonatomic) float rating;
@property (assign) BOOL editable;
@property (strong) NSMutableArray * imageViews;
@property (assign, nonatomic) int maxRating;
@property (assign) int midMargin;
@property (assign) int leftMargin;
@property (assign) CGSize minImageSize;
@property (assign) id <RateViewDelegate> delegate;

@end

First we set up a delegate so we can notify our view controller when the rating changes. We could have done this via blocks or a target/selector as well, but I thought this was simpler.

Next, we set up a bunch of properties:

• Three UIImages to represent not selected, half selected, and fully selected.
• A variable to keep track of our current rating.
• A boolean to keep track of whether this view should be editable or not. For example, sometimes we may wish to just display a rating without letting the user edit it.
• An array to keep track of the image views we’ll have as children of this view. Note we could have implemented this by just drawing the images in drawRect, but this was simpler (albeit slower performance).
• The maximum value for a rating. This actually allows us to support other numbers of stars than 5 – for example, maybe we want 3 stars, or 10 stars? Also note the minimum is an assumed 0.
• Variables to keep track of spacing in case our user wants to change it: the margin between images, the left margin, and a minimum image size.
• Finally a variable to keep track of our delegate.

Initialization and Cleanup

Next, we add in the boilerplate code for the construction of our classes. Replace RateView.m with the following:

#import "RateView.h"

@implementation RateView

@synthesize notSelectedImage = _notSelectedImage;
@synthesize halfSelectedImage = _halfSelectedImage;
@synthesize fullSelectedImage = _fullSelectedImage;
@synthesize rating = _rating;
@synthesize editable = _editable;
@synthesize imageViews = _imageViews;
@synthesize maxRating = _maxRating;
@synthesize midMargin = _midMargin;
@synthesize leftMargin = _leftMargin;
@synthesize minImageSize = _minImageSize;
@synthesize delegate = _delegate;

- (void)baseInit {
    _notSelectedImage = nil;
    _halfSelectedImage = nil;
    _fullSelectedImage = nil;
    _rating = 0;
    _editable = NO;    
    _imageViews = [[NSMutableArray alloc] init];
    _maxRating = 5;
    _midMargin = 5;
    _leftMargin = 0;
    _minImageSize = CGSizeMake(5, 5);
    _delegate = nil;    
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self baseInit];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder {
    if ((self = [super initWithCoder:aDecoder])) {
        [self baseInit];
    }
    return self;
}

@end

This is all pretty boilerplate stuff where we initialize our instance variables to default values. Note that we support both initWithFrame and initWithCoder so that our view controller can add us via a XIB or programatically.

Refreshing Our View

Pretend that the view controller has set up our instance variables with valid images, ratings, maxRating, etc, and that we’ve created our UIImageView subviews. Well we need to write a method to refresh the display based on the current rating. Add this method to the file next:

- (void)refresh {
    for(int i = 0; i < self.imageViews.count; ++i) {
        UIImageView *imageView = [self.imageViews objectAtIndex:i];
        if (self.rating >= i+1) {
            imageView.image = self.fullSelectedImage;
        } else if (self.rating > i) {
            imageView.image = self.halfSelectedImage;
        } else {
            imageView.image = self.notSelectedImage;
        }
    }
}

Pretty simple stuff here – we just loop through our list of images and set the appropriate image based on the rating.

Layout Subviews

Probably the most important function in our file is the implementation of layoutSubviews. This function gets called whenever the frame of our view changes, and we’re expected to set up the frames of all of our subviews to the appropriate size for that space. So add this function next:

- (void)layoutSubviews {
    [super layoutSubviews];
    
    if (self.notSelectedImage == nil) return;
    
    float desiredImageWidth = (self.frame.size.width - (self.leftMargin*2) - (self.midMargin*self.imageViews.count)) / self.imageViews.count;
    float imageWidth = MAX(self.minImageSize.width, desiredImageWidth);
    float imageHeight = MAX(self.minImageSize.height, self.frame.size.height);
    
    for (int i = 0; i < self.imageViews.count; ++i) {
        
        UIImageView *imageView = [self.imageViews objectAtIndex:i];
        CGRect imageFrame = CGRectMake(self.leftMargin + i*(self.midMargin+imageWidth), 0, imageWidth, imageHeight);
        imageView.frame = imageFrame;
        
    }    
    
}

We first bail if our notSelectedImage isn't set up yet.

But if it is, we just do some simple calculations to figure out how to set the frames for each UIImageView.

The images are laid out like the following to fill the entire frame: left margin, image #1, mid margin, ..., image #n, left margin.

So if we know the full size of the frame, we can subtract out the margins and divide by the number of images to figure out how wide to make each of the UIImageViews.

Once we know that, we simply loop through and update the frames for each UIImageView.

Setting properties

Since we don't know the order in which the view controller is going to set our properties (especially since they could even change mid-display), we have to be careful about how we construct our subviews, etc. This is the approach I took to solve the problem, if anyone else has a different approach I'd love to hear!

- (void)setMaxRating:(int)maxRating {
    _maxRating = maxRating;
    
    // Remove old image views
    for(int i = 0; i < self.imageViews.count; ++i) {
        UIImageView *imageView = (UIImageView *) [self.imageViews objectAtIndex:i];
        [imageView removeFromSuperview];
    }
    [self.imageViews removeAllObjects];
    
    // Add new image views
    for(int i = 0; i < maxRating; ++i) {
        UIImageView *imageView = [[UIImageView alloc] init];
        imageView.contentMode = UIViewContentModeScaleAspectFit;
        [self.imageViews addObject:imageView];
        [self addSubview:imageView];
    }
    
    // Relayout and refresh
    [self setNeedsLayout];
    [self refresh];
}

- (void)setNotSelectedImage:(UIImage *)image {
    _notSelectedImage = image;
    [self refresh];
}

- (void)setHalfSelectedImage:(UIImage *)image {
    _halfSelectedImage = image;
    [self refresh];
}

- (void)setFullSelectedImage:(UIImage *)image {
    _fullSelectedImage = image;
    [self refresh];
}

- (void)setRating:(float)rating {
    _rating = rating;
    [self refresh];
}

The most important method is the setMaxRating method - because this determines how many UIImageView subviews we have. So when this changes, we remove any existing image views and create the appropriate amount. Of course, once this happens we need to make sure layoutSubviews and refresh is called, so we call setNeedsLayout and refresh.

Similarly, when any of the images or the rating changes, we need to make sure our refresh method gets called so our display is consistent.