实现不规则形状的按钮

用到了四个文件：

UIImage+ColorAtPixel.h UIImage+ColorAtPixel.m OBShapedButton.h OBShapedButton.m

作者：Ole Begemann

/*
 Copyright (c) 2009 Ole Begemann
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */

/*
 UIImage+ColorAtPixel.h

 Created by Ole Begemann
 October, 2009
 */
 
#import <UIKit/UIKit.h>

/*
 A category on UIImage that enables you to query the color value of arbitrary 
 pixels of the image.
 */
@interface UIImage (ColorAtPixel)

- (UIColor *)colorAtPixel:(CGPoint)point;

@end

/*
 Copyright (c) 2009 Ole Begemann
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */

/*
 UIImage+ColorAtPixel.m
 
 Created by Ole Begemann
 October, 2009
 */

#import <CoreGraphics/CoreGraphics.h>

#import "UIImage+ColorAtPixel.h"


@implementation UIImage (ColorAtPixel)

/*
 Returns the color of the image pixel at point. Returns nil if point lies outside the image bounds.
 If the point coordinates contain decimal parts, they will be truncated.
 
 To get at the pixel data, this method must draw the image into a bitmap context.
 For minimal memory usage and optimum performance, only the specific requested
 pixel is drawn.
 If you need to query pixel colors for the same image repeatedly (e.g., in a loop),
 this approach is probably less efficient than drawing the entire image into memory
 once and caching it.
 */
- (UIColor *)colorAtPixel:(CGPoint)point {
    // Cancel if point is outside image coordinates
    if (!CGRectContainsPoint(CGRectMake(0.0f, 0.0f, self.size.width, self.size.height), point)) {
        return nil;
    }
    
    
    // Create a 1x1 pixel byte array and bitmap context to draw the pixel into.
    // Reference: http://stackoverflow.com/questions/1042830/retrieving-a-pixel-alpha-value-for-a-uiimage
    NSInteger pointX = trunc(point.x);
    NSInteger pointY = trunc(point.y);
    CGImageRef cgImage = self.CGImage;
    NSUInteger width = self.size.width;
    NSUInteger height = self.size.height;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    int bytesPerPixel = 4;
    int bytesPerRow = bytesPerPixel * 1;
    NSUInteger bitsPerComponent = 8;
    unsigned char pixelData[4] = { 0, 0, 0, 0 };
    CGContextRef context = CGBitmapContextCreate(pixelData, 
                                                 1,
                                                 1,
                                                 bitsPerComponent, 
                                                 bytesPerRow, 
                                                 colorSpace,
                                                 kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGColorSpaceRelease(colorSpace);
    CGContextSetBlendMode(context, kCGBlendModeCopy);

    // Draw the pixel we are interested in onto the bitmap context
    CGContextTranslateCTM(context, -pointX, pointY-(CGFloat)height);
    CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage);
    CGContextRelease(context);
    
    // Convert color values [0..255] to floats [0.0..1.0]
    CGFloat red   = (CGFloat)pixelData[0] / 255.0f;
    CGFloat green = (CGFloat)pixelData[1] / 255.0f;
    CGFloat blue  = (CGFloat)pixelData[2] / 255.0f;
    CGFloat alpha = (CGFloat)pixelData[3] / 255.0f;
    return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
}

@end

/*
 Copyright (c) 2009 Ole Begemann
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */

/*
 OBShapedButton.h
 
 Created by Ole Begemann
 October, 2009
 */

#import <UIKit/UIKit.h>


/*
 OBShapedButton is a UIButton subclass optimized for non-rectangular button shapes.
 Instances of OBShapedButton respond to touches only in areas where the image that is
 assigned to the button for UIControlStateNormal is non-transparent.
 
 Usage:
 - Add OBShapedButton.h, OBShapedButton.m, UIImage+ColorAtPixel.h, and UIImage+ColorAtPixel.m
   to your Xcode project.
 - Design your UI in Interface Builder with UIButtons as usual. Set the Button type to Custom
   and provide transparent PNG images for the different control states as needed.
 - In the Identity Inspector in Interface Builder, set the Class of the button to OBShapedButton.
   That's it! Your button will now only respond to touches where the PNG image for the normal
   control state is non-transparent.
 */



// -[UIView hitTest:withEvent: ignores views that an alpha level less than 0.1.
// So we will do the same and treat pixels with alpha < 0.1 as transparent.
#define kAlphaVisibleThreshold (0.1f)


@interface OBShapedButton : UIButton {
    // Our class interface is empty. OBShapedButton only overwrites one method of UIView.
    // It has no attributes of its own.
}

@end

/*
 Copyright (c) 2009 Ole Begemann
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */

/*
 OBShapedButton.m
 
 Created by Ole Begemann
 October, 2009
 */

#import "OBShapedButton.h"
#import "UIImage+ColorAtPixel.h"


@interface OBShapedButton ()

@property (nonatomic, assign) CGPoint previousTouchPoint;
@property (nonatomic, assign) BOOL previousTouchHitTestResponse;

- (void)resetHitTestCache;

@end


@implementation OBShapedButton

@synthesize previousTouchPoint = _previousTouchPoint;
@synthesize previousTouchHitTestResponse = _previousTouchHitTestResponse;

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

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


#pragma mark - Hit testing

- (BOOL)isAlphaVisibleAtPoint:(CGPoint)point forImage:(UIImage *)image
{
    // Correct point to take into account that the image does not have to be the same size
    // as the button. See https://github.com/ole/OBShapedButton/issues/1
    CGSize iSize = image.size;
    CGSize bSize = self.bounds.size;
    point.x *= (bSize.width != 0) ? (iSize.width / bSize.width) : 1;
    point.y *= (bSize.height != 0) ? (iSize.height / bSize.height) : 1;

    CGColorRef pixelColor = [[image colorAtPixel:point] CGColor];
    CGFloat alpha = CGColorGetAlpha(pixelColor);
    return alpha >= kAlphaVisibleThreshold;
}


// UIView uses this method in hitTest:withEvent: to determine which subview should receive a touch event.
// If pointInside:withEvent: returns YES, then the subview’s hierarchy is traversed; otherwise, its branch
// of the view hierarchy is ignored.
- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event 
{
    // Return NO if even super returns NO (i.e., if point lies outside our bounds)
    BOOL superResult = [super pointInside:point withEvent:event];
    if (!superResult) {
        return superResult;
    }

    // Don't check again if we just queried the same point
    // (because pointInside:withEvent: gets often called multiple times)
    if (CGPointEqualToPoint(point, self.previousTouchPoint)) {
        return self.previousTouchHitTestResponse;
    } else {
        self.previousTouchPoint = point;
    }
    
    // We can't test the image's alpha channel if the button has no image. Fall back to super.
    UIImage *buttonImage = [self imageForState:UIControlStateNormal];
    UIImage *buttonBackground = [self backgroundImageForState:UIControlStateNormal];

    BOOL response = NO;
    
    if (buttonImage == nil && buttonBackground == nil) {
        response = YES;
    }
    else if (buttonImage != nil && buttonBackground == nil) {
        response = [self isAlphaVisibleAtPoint:point forImage:buttonImage];
    }
    else if (buttonImage == nil && buttonBackground != nil) {
        response = [self isAlphaVisibleAtPoint:point forImage:buttonBackground];
    }
    else {
        if ([self isAlphaVisibleAtPoint:point forImage:buttonImage]) {
            response = YES;
        } else {
            response = [self isAlphaVisibleAtPoint:point forImage:buttonBackground];
        }
    }
    
    self.previousTouchHitTestResponse = response;
    return response;
}


// Reset the Hit Test Cache when a new image is assigned to the button
- (void)setImage:(UIImage *)image forState:(UIControlState)state
{
    [super setImage:image forState:state];
    [self resetHitTestCache];
}

- (void)setBackgroundImage:(UIImage *)image forState:(UIControlState)state
{
    [super setBackgroundImage:image forState:state];
    [self resetHitTestCache];
}

- (void)resetHitTestCache
{
    self.previousTouchPoint = CGPointMake(CGFLOAT_MIN, CGFLOAT_MIN);
    self.previousTouchHitTestResponse = NO;
}

@end

使用：

使用IB，添加一个UIButton，把关联类选择为OBShapedButton，把Button的Type修改为Custom，添加一个异形的Image，然后编译运行即可看到效果。