[iOS]点击UIImageView获取点击处颜色

最近在一个项目中，需要实现这么一个效果：显示一张地图，通过点击不同位置，来切换点击处的行政区域，效果图如下：

map.gif

在此记录一下实现思路：

• 1.首先要有一组需要展示的不同地区的图片，我的图片如下：

maps.png

这里要注意，要留意map_whs这张图片的尺寸，因为代码中需要使用到这个尺寸。

• 2.然后，你需要知道每个地区所对应的地图颜色，我的地图对于颜色如下：

colors.png

我自己写了个JSON文件，用来保存对应的颜色、名称以及图片名称。

• 3.在代码中，创建一个UIImageView，这个UIImageView的宽高比例要与刚才提到的map_whs图片的宽高比例一致，同时，计算出UIImageView的宽(或者高)与map_whs的宽(或者高)德比例，然后为UIImageView添加点击事件：

    self.mapImageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, self.nameLabel.plt_y + self.nameLabel.plt_height, self.view.plt_width, self.view.plt_width / (kMapImageWidth / kMapImageHeight))];
    UITapGestureRecognizer *mapImageViewTGR = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(mapImageViewTGRAction:)];
    [self.mapImageView addGestureRecognizer:mapImageViewTGR];
    self.mapImageView.userInteractionEnabled = YES;
    [self.view addSubview:self.mapImageView];

• 4.处理点击事件，获取到的点击位置，要根据上一步计算的比例来对应到map_whs这张图片的点上：

- (void)mapImageViewTGRAction:(UITapGestureRecognizer *)tgr
{
    //触点位置
    CGPoint touchLocation = [tgr locationInView:self.mapImageView];
    
    if (touchLocation.x > 0 && touchLocation.x <= self.mapImageView.plt_width && touchLocation.y > 0 && touchLocation.y <= self.mapImageView.plt_height) {
        //触点颜色
        UIColor *positionColor=[self getColor:touchLocation];
        for (NSDictionary *dic in self.txtArr) {
            UIColor *color = PltColorWithHEX(dic[kMapTxtColor]);
            if (CGColorEqualToColor(color.CGColor, positionColor.CGColor)) {
                [self setUpImage:dic];
                break;
            }
        }
    }
}

#pragma mark - 获取点击颜色
- (UIColor *)getColor:(CGPoint)point
{
    UIColor* color = [UIColor whiteColor];
    if (point.x > 0 && point.y > 0) {
        
        CGFloat ratio = kMapImageWidth / self.mapImageView.plt_width;
        
        CGPoint realPoint = CGPointMake(point.x * ratio, point.y * ratio);
        CGImageRef inImage = [UIImage imageNamed:@"map_whs"].CGImage;
        CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
        if (cgctx == NULL) {
            return nil;
        }
        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);
        
        // Now we can get a pointer to the image data associated with the bitmap
        // context.
        unsigned char* data = CGBitmapContextGetData (cgctx);
        if (data != NULL)
        {
            //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.
            @try
            {
                int offset = 4*((w*round(realPoint.y))+round(realPoint.x));
                //NSLog(@"offset: %d", offset);
                int alpha =  data[offset];
                int red = data[offset+1];
                int green = data[offset+2];
                int blue = data[offset+3];
                //            NSLog(@"offset: %i colors: RGB A %i %i %i  %i",offset,red,green,blue,alpha);
                color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
            }
            @catch (NSException * e)
            {
                NSLog(@"%@",[e reason]);
            }
            @finally
            {
                
            }
            
        }
        
        // 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;
    int             bitmapByteCount;
    int             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   = (int)(pixelsWide * 4);
    bitmapByteCount     =(int)(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;
}

Demo地址，TouchColor-Demo文件夹