What is a Delegate? Technically speaking, a delegate is just an object that acts on behalf of another object.
The delegating object is typically a framework object, and the delegate is typically a custom controller object. In a managed memory environment, the delegating object maintains a weak reference to its delegate, and delegate object maintains a strong reference.
okay, talk is cheap. Let's see it in action! First, create a new file, I call it BgSlider. make it subclass of UISlider. open up your BgSlider.h file. add following code:
@class BgSlider; // Declaring my own class, the compiler will yell at you without it.
@protocol BgSliderDelegate // must adopt minimum required methods from NSObject! The NSObject protocol contains a method called respondsToSelector:, Calling a method that isn't implemented by the delegate object will cause your application to crash.
// declaring my methods @optional -(void)BgSliderDidChange:(BgSlider *)BgSlider withValue:(CGFloat)value; @required -(CGFloat)startPositionForBgSlider:(BgSlider *)BgSlider; @end
@interface BgSlider : UISlider @property (nonatomic, weak) id sliderDelegate; // must be weak if you are using ARC!
// making Custom initializer.
- (id)initWithFrame:(CGRect)frame withDelegate:(id)delegate; @end
open up your BgSlider.m Creating a custom initializer is the key! Setting the delegate during initialization allows the delegate method to be called immediately. note: initializer is called before anything drawn on the screen.
- (id)initWithFrame:(CGRect)frame withDelegate:(id)delegate { self = [super initWithFrame:frame]; if (self) { // Set delegate self.sliderDelegate = delegate; // Set delegate object! self.value = [_sliderDelegate startPositionForBgSlider:self]; // set value self.minimumTrackTintColor = [UIColor darkGrayColor]; // set slider track color } return self; }
add the following method. each time a slider peg moves, a message is sent to the delegate object.
-
(void)setValue:(float)value animated:(BOOL)animated { //### Must call super class when overriding the value [super setValue:value animated:animated];
if (self.sliderDelegate != nil && [self.sliderDelegate respondsToSelector:@selector(BgSliderDidChange:withValue:)]){ [[self sliderDelegate] BgSliderDidChange:self withValue:value]; }
}
Here is your ViewController.h file. @interface ViewController : UIViewController
Implement following methods in your ViewController.m file.
- (void)viewDidLoad { [super viewDidLoad]; [self addSlider]; }
-(void)addSlider{ CGFloat sliderColorPosition = 0.3f; self.view.backgroundColor = [UIColor colorWithRed:sliderColorPosition green:sliderColorPosition blue:sliderColorPosition alpha:1.0f];
// ### Instaniate sliders from RGB Values
CGRect redSliderFrame = CGRectMake(20.0f, 180.0f, 280.0f, 30.0f);
BgSlider *redSlider = [[BgSlider alloc] initWithFrame:redSliderFrame withDelegate:self];
redSlider.tag = 1;
[self.view addSubview:redSlider];
CGRect greenSliderFrame = CGRectMake(20.0f, 230.0f, 280.0f, 30.0f);
BgSlider *greenSlider = [[BgSlider alloc] initWithFrame:greenSliderFrame withDelegate:self];
greenSlider.tag = 2;
[self.view addSubview:greenSlider];
CGRect blueSliderFrame = CGRectMake(20.0f, 280.0f, 280.0f, 30.0f);
BgSlider *blueSlider = [[BgSlider alloc] initWithFrame:blueSliderFrame withDelegate:self];
blueSlider.tag = 3;
[self.view addSubview:blueSlider];
}
-(CGFloat)startPositionForBgSlider:(BgSlider *)BgSlider{ CGFloat startPos = 0.5f; return startPos; }
-(void)BgSliderDidChange:(BgSlider *)BgSlider withValue:(CGFloat)value{ if (BgSlider.tag == 1) { //Red Slider CGColorRef bgColor = self.view.backgroundColor.CGColor; const CGFloat *colorsPointer = CGColorGetComponents(bgColor); CGFloat currentGreen = colorsPointer[1]; CGFloat currentBlue = colorsPointer[2]; self.view.backgroundColor = [UIColor colorWithRed:value green:currentGreen blue:currentBlue alpha:1.0f];
}
if (BgSlider.tag == 2) { //Green Slider
CGColorRef bgColor = self.view.backgroundColor.CGColor;
const CGFloat *colorsPointer = CGColorGetComponents(bgColor);
CGFloat currentRed = colorsPointer[0];
CGFloat currentBlue = colorsPointer[2];
self.view.backgroundColor = [UIColor colorWithRed:currentRed green:value blue:currentBlue alpha:1.0f];
}
if (BgSlider.tag == 3) { //Blue Slider
CGColorRef bgColor = self.view.backgroundColor.CGColor;
const CGFloat *colorsPointer = CGColorGetComponents(bgColor);
CGFloat currentRed = colorsPointer[0];
CGFloat currentGreen = colorsPointer[1];
self.view.backgroundColor = [UIColor colorWithRed:currentRed green:currentGreen blue:value alpha:1.0f];
}
}
build and run! update your Xcode to current version if this program doesn't work on your computer. Enjoy!
By the way, Don't forget to check out more cool stuffs from my website. http://www.8land.org/iOS_programming/kickstarter_project
Your feedback is welcomed! Thank You!