Question

I am new to iphone and xcode. This may be a very simple question but I could not find an example code in books. I want to do the following:

• Have 2 UIView on the screen
• Each view will step through the color of the rainbow (red/orange/yellow/green/blue/indigo/violet) using gesture recognizer, e.g., if the current color is green, if the user swipes up the UIView changes to yellow, if the user swipes down the UIView changes to blue.
• Hence, each view will need to keep the current color and respond to the swipes accordingly.

I understand how to implement the detection of swipes using gesture recognizer but I don’t know how to have each view keep a separate variable for the current color. I want a generic code because there will be more than 2 UIViews in my application once I figure out how it is done.

Thanks in advance.

Answer 1

Since you are going to maintain an array of colors, say colorsArray, and assign views their color from that selection. You can do this in the swipe handler.

- (void)handleSwipe:(UISwipeGestureRecognizer*)swipeGesture {
    UIView *view = swipeGesture.view;

    NSInteger currentColorIndex = [colorsArray indexOfObject:view.backgroundColor];
    NSInteger nextColorIndex = currentColorIndex + 1;
    if ( nextColorIndex == [colorsArray count] ) {
        nextColorIndex = 0;
    }

    view.backgroundColor = [colorsArray objectAtIndex:nextColorIndex];
}

This way you don’t need to subclass.

Subclassing

You can subclass UIView and add your own instance variables to it. Say,

@interface RainbowView: UIView {
    NSInteger currentColorIndex;
}

@property (nonatomic, assign) NSInteger currentColorIndex;
...

@end

@implementation RainbowView

@synthesize currentColorIndex;

...

@end

In your gesture handling method,

- (void)handleSwipe:(UISwipeGestureRecognizer*)swipeGesture {
    RainbowView *aView = (RainbowView*)swipeGesture.view;

    // Get the next color index to aView.currentColorIndex;
    aView.backgroundColor = [colorsArray objectAtIndex:nextColorIndex];
    aView.currentColorIndex = nextColorIndex;
}