动态获取图片色值，黑点坐标

如图：点击或者根据图中黑点滑动获取图片色值及黑点坐标。ColorImageView是继承UIImageView的封装，用起来很方便。

下面我们先讲demo的ViewController布局：

1，引进ColorImageView.h ；

#import "ColorImageView.h"          

2, 声明了两个label用于显示rag值 及黑点位置；

@interface ViewController ()@property (nonatomic,strong)UILabel *rgbLabel;//rgba@property (nonatomic,strong)UILabel *locationLabel;//黑点位置@end

3, 就是把声明的label在 viewDidLoad 中进行添加：

    _rgbLabel = [[UILabel alloc] init];    _rgbLabel.frame=CGRectMake(10,60, self.view.frame.size.width-20, 23);    _rgbLabel.backgroundColor = [UIColor clearColor];    _rgbLabel.font = [UIFont systemFontOfSize:13 ];    _rgbLabel.textAlignment = NSTextAlignmentCenter;    _rgbLabel.textColor = [UIColor blackColor];    _rgbLabel.text = @"点击或移动下面的彩色图片，获取色值！";    [self.view addSubview:_rgbLabel];    _locationLabel = [[UILabel alloc] init];    _locationLabel.frame=CGRectMake(10,90, self.view.frame.size.width-20, 23);    _locationLabel.backgroundColor = [UIColor clearColor];    _locationLabel.font = [UIFont systemFontOfSize:13 ];    _locationLabel.textAlignment = NSTextAlignmentCenter;    _locationLabel.textColor = [UIColor whiteColor];    [self.view addSubview:_locationLabel];

4，把封装的ColorImageView也添加在viewDidLoad中，关于ColorImageView值传出我用的是一个block，如果对block不理解，就自己上网查咯！

    ColorImageView *colorImageView = [[ColorImageView alloc] initWithFrame:CGRectMake((self.view.frame.size.width-248)/2,130, 248, 248)];    colorImageView.backgroundColor = [UIColor clearColor];    colorImageView.userInteractionEnabled = YES;    colorImageView.image = [UIImage imageNamed:@"color_s"];    //避免循序引用 弱化    __weak typeof(self) weakSelf = self;    colorImageView.block =^ (NSString *rgbaString,NSString *locationString,UIColor *color){        weakSelf.rgbLabel.text = rgbaString;        weakSelf.rgbLabel.textColor = color;        weakSelf.locationLabel.text = locationString;    };    [self.view addSubview:colorImageView];

上面ViewController的介绍完了，下面就是（重头戏）ColorImageView的封装介绍：

1，开始就是控件的添加 ，有注释 ；不用多说直接粘代码：

////ColorImageVIew.m//  TableView_choose////  Created by Simon on 16/6/15.//  Copyright © 2016年 Simon. All rights reserved.//#import "ColorImageView.h"#define radiusColor  120 //图片半径值@interface ColorImageView ()@property (nonatomic,strong)UIImageView *selectColorIamge;//黑点@property (nonatomic,copy)NSString *rgbaString;//rgb字符串@property (nonatomic,copy)NSString *locationString;//黑点位置字符串@end@implementation ColorImageView- (id)initWithFrame:(CGRect)frame{    self = [super initWithFrame:frame];    if (self) {        // Initialization code        _selectColorIamge = [[UIImageView alloc] init];        _selectColorIamge.backgroundColor = [UIColor blackColor];        _selectColorIamge.frame=CGRectMake((frame.size.width-16)/2, (frame.size.height-16)/2, 16, 16);        _selectColorIamge.layer.cornerRadius = 8;        _selectColorIamge.layer.masksToBounds = YES;        [self addSubview:_selectColorIamge];    }    return self;}

2，用系统自带touchesBegan touchesMoved touchesEnded方法实现我们的点击，移动；在移动中要限制黑点不能逃出色值图片的范围，就有了一个关于高中数学的运算，挺有意思的（不妨看看，是不是很多人都忘了）！这里block的传值就是这一句_block(_rgbaString,_locationString,color);

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {    UITouch* touch = [touches anyObject];    CGPoint point = [touch locationInView:self]; //where image was tapped    CGPoint center = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);    float distance = [self distanceFromPointX:center distanceToPointY:point];    if(distance<radiusColor){        _selectColorIamge.center =point;        dispatch_async(dispatch_get_main_queue(), ^{            UIColor* color = [self getPixelColorAtLocation:point];            if (_block) {                _block(_rgbaString,_locationString,color);            }         });     }}- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{    UITouch* touch = [touches anyObject];    CGPoint point = [touch locationInView:self]; //where image was tapped    CGPoint center = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);    float distance = [self distanceFromPointX:center distanceToPointY:point];    if(distance<radiusColor){        _selectColorIamge.center =point;        dispatch_async(dispatch_get_main_queue(), ^{            UIColor* color = [self getPixelColorAtLocation:point];            if (_block) {                _block(_rgbaString,_locationString,color);            }        });    }else{        double xx=powf(point.x-radiusColor,2);        double yy=powf(point.y-radiusColor,2);         double xy=xx+yy;//圆心到手指停留处的距离(平方)        double poingXy=sqrtf(xy);//圆心到手指停留处的距离(直线）        double Geometric = (radiusColor-1)/poingXy;//等比值        double groundx=(point.x-radiusColor)*Geometric+radiusColor;//圆边x坐标        double groundy=(point.y-radiusColor)*Geometric+radiusColor;//圆边y坐标        CGPoint groundByoed = CGPointMake(groundx, groundy);         _selectColorIamge.center =groundByoed;        dispatch_async(dispatch_get_main_queue(), ^{            UIColor* color = [self getPixelColorAtLocation:point];            if (_block) {                _block(_rgbaString,_locationString,color);            }        });      }}- (void) touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {    UITouch* touch = [touches anyObject];    CGPoint point = [touch locationInView:self]; //    CGPoint center = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);    float distance = [self distanceFromPointX:center distanceToPointY:point];    if(distance<radiusColor){        _selectColorIamge.center =point;        dispatch_async(dispatch_get_main_queue(), ^{            UIColor* color = [self getPixelColorAtLocation:point];            if (_block) {                _block(_rgbaString,_locationString,color);            }        });    }   }

3，上面看到（distanceFromPointX：distanceToPointY：）一直都有调用，他是干什么的呢；其实很简单，就是把黑点限制在牢里用的（不逃出色值图片范围）：

 //计算圆点所在位置-(float)distanceFromPointX:(CGPoint)start distanceToPointY:(CGPoint)end{    float distance;    //下面就是高中的数学，不详细解释了    CGFloat xDist = (end.x - start.x);    CGFloat yDist = (end.y - start.y);    distance = sqrt((xDist * xDist) + (yDist * yDist));    return distance;}

4，（getPixelColorAtLocation：）和（createARGBBitmapContextFromImage：）这两个方法呢，就是关键所在了，把在色值图片上黑点的位置转化成我们想要的值。。不明白的多看看，实在不行就找度娘！

#pragma mark private- (UIColor*)getPixelColorAtLocation:(CGPoint)point {    UIColor* color = nil;    CGImageRef inImage = self.image.CGImage;    // Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, Blue    CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];    if (cgctx == NULL) { return nil; /* error */ }    size_t w = CGImageGetWidth(inImage);    size_t h = CGImageGetHeight(inImage);    CGRect rect = {{0,0},{w,h}};    // Draw the image to the bitmap context. Once we draw, the memory    // allocated for the context for rendering will then contain the    // raw image data in the specified color space.    CGContextDrawImage(cgctx, rect, inImage);    if(rect.size.width==480){        point.x = point.x*2;        point.y = point.y*2;    }    // Now we can get a pointer to the image data associated with the bitmap    // context.    unsigned char* data = CGBitmapContextGetData (cgctx);    if (data != NULL) {        //读取RGB颜色值        //offset locates the pixel in the data from x,y.        //4 for 4 bytes of data per pixel, w is width of one row of data.        int offset = 4*((w*round(point.y))+round(point.x));        int alpha =  data[offset];        unsigned int red = data[offset+1];        unsigned int green = data[offset+2];        unsigned int blue = data[offset+3];        color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];        _rgbaString = [NSString stringWithFormat:@"RGBA值： red:%d  green:%d  blue:%d  alpha:%d",red,green,blue,alpha];        _locationString =[NSString stringWithFormat:@"黑点位置point： %.2f  %.2f",point.x,point.y];    }    // When finished, release the context    CGContextRelease(cgctx);    // Free image data memory for the context    if (data) {        free(data);    }    return color;}- (CGContextRef)createARGBBitmapContextFromImage:(CGImageRef) inImage {    CGContextRef    context = NULL;    CGColorSpaceRef colorSpace;    void *          bitmapData;    long             bitmapByteCount;    long             bitmapBytesPerRow;    // Get image width, height. We'll use the entire image.    size_t pixelsWide = CGImageGetWidth(inImage);    size_t pixelsHigh = CGImageGetHeight(inImage);    // Declare the number of bytes per row. Each pixel in the bitmap in this    // example is represented by 4 bytes; 8 bits each of red, green, blue, and    // alpha.    bitmapBytesPerRow   = (pixelsWide * 4);    bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);    // Use the generic RGB color space.    colorSpace = CGColorSpaceCreateDeviceRGB();    if (colorSpace == NULL)    {        fprintf(stderr, "Error allocating color space\n");        return NULL;    }    // Allocate memory for image data. This is the destination in memory    // where any drawing to the bitmap context will be rendered.    bitmapData = malloc( bitmapByteCount );    if (bitmapData == NULL)    {        fprintf (stderr, "Memory not allocated!");        CGColorSpaceRelease( colorSpace );        return NULL;    }    // Create the bitmap context. We want pre-multiplied ARGB, 8-bits    // per component. Regardless of what the source image format is    // (CMYK, Grayscale, and so on) it will be converted over to the format    // specified here by CGBitmapContextCreate.    context = CGBitmapContextCreate (bitmapData,                                     pixelsWide,                                     pixelsHigh,                                     8,      // bits per component                                     bitmapBytesPerRow,                                     colorSpace,                                     kCGImageAlphaPremultipliedFirst);    if (context == NULL)    {        free (bitmapData);        //fprintf (stderr, "Context not created!");    }    // Make sure and release colorspace before returning    CGColorSpaceRelease( colorSpace );    return context；}