图片围绕中心截取显示

系统返回的图片的大小和需要显示的ImageView差别过大,直接显示导致图片严重变形,这时候需要对图片进行截取

1.首先使用SD下载图片 直接上代码 粘贴就可以使用

1.1创建工具类 Singleton.h 直接粘贴即可

#define singleton_interface(className) 
+ (className *)shared##className;


#define singleton_implementation(class) 
static class *_instance; 

+ (id)allocWithZone:(struct _NSZone *)zone 
{ 
    static dispatch_once_t onceToken; 
    dispatch_once(&onceToken, ^{ 
        _instance = [super allocWithZone:zone]; 
    }); 

    return _instance; 
} 

+ (instancetype)shared##class 
{ 
    if (_instance == nil) { 
        _instance = [[class alloc] init]; 
    } 

    return _instance; 
}

1.2 创建一个继承与NSObject的类

#import <Foundation/Foundation.h>
#import "Singleton.h"
@interface Single : NSObject
singleton_interface(Single)


+(CGSize)downloadImageSizeWithURL:(id)imageURL;
@end

#import "Single.h"
#import "SDImageCache.h"
@implementation Single
singleton_implementation(Single)
+(CGSize)downloadImageSizeWithURL:(id)imageURL
{
    NSURL* URL = nil;
    if([imageURL isKindOfClass:[NSURL class]]){
        URL = imageURL;
    }
    if([imageURL isKindOfClass:[NSString class]]){
        URL = [NSURL URLWithString:imageURL];
    }
    if(URL == nil)
        return CGSizeZero;
    
    NSString* absoluteString = URL.absoluteString;
    
#ifdef dispatch_main_sync_safe
    if([[SDImageCache sharedImageCache] diskImageExistsWithKey:absoluteString])
    {
        UIImage* image = [[SDImageCache sharedImageCache] imageFromMemoryCacheForKey:absoluteString];
        if(!image)
        {
            NSData* data = [[SDImageCache sharedImageCache] performSelector:@selector(diskImageDataBySearchingAllPathsForKey:) withObject:URL.absoluteString];
            image = [UIImage imageWithData:data];
        }
        if(image)
        {
            return image.size;
        }
    }
#endif
    
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:URL];
    NSString* pathExtendsion = [URL.pathExtension lowercaseString];
    
    CGSize size = CGSizeZero;
    if([pathExtendsion isEqualToString:@"png"]){
        size =  [self downloadPNGImageSizeWithRequest:request];
    }
    else if([pathExtendsion isEqual:@"gif"])
    {
        size =  [self downloadGIFImageSizeWithRequest:request];
    }
    else{
        size = [self downloadJPGImageSizeWithRequest:request];
    }
    if(CGSizeEqualToSize(CGSizeZero, size))
    {
        NSData* data = [NSURLConnection sendSynchronousRequest:[NSURLRequest requestWithURL:URL] returningResponse:nil error:nil];
        UIImage* image = [UIImage imageWithData:data];
        if(image)
        {
#ifdef dispatch_main_sync_safe
            [[SDImageCache sharedImageCache] storeImage:image recalculateFromImage:YES imageData:data forKey:URL.absoluteString toDisk:YES];
#endif
            size = image.size;
        }
    }
    return size;
}
+(CGSize)downloadPNGImageSizeWithRequest:(NSMutableURLRequest*)request
{
    [request setValue:@"bytes=16-23" forHTTPHeaderField:@"Range"];
    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
    if(data.length == 8)
    {
        int w1 = 0, w2 = 0, w3 = 0, w4 = 0;
        [data getBytes:&w1 range:NSMakeRange(0, 1)];
        [data getBytes:&w2 range:NSMakeRange(1, 1)];
        [data getBytes:&w3 range:NSMakeRange(2, 1)];
        [data getBytes:&w4 range:NSMakeRange(3, 1)];
        int w = (w1 << 24) + (w2 << 16) + (w3 << 8) + w4;
        int h1 = 0, h2 = 0, h3 = 0, h4 = 0;
        [data getBytes:&h1 range:NSMakeRange(4, 1)];
        [data getBytes:&h2 range:NSMakeRange(5, 1)];
        [data getBytes:&h3 range:NSMakeRange(6, 1)];
        [data getBytes:&h4 range:NSMakeRange(7, 1)];
        int h = (h1 << 24) + (h2 << 16) + (h3 << 8) + h4;
        return CGSizeMake(w, h);
    }
    return CGSizeZero;
}
+(CGSize)downloadGIFImageSizeWithRequest:(NSMutableURLRequest*)request
{
    [request setValue:@"bytes=6-9" forHTTPHeaderField:@"Range"];
    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
    if(data.length == 4)
    {
        short w1 = 0, w2 = 0;
        [data getBytes:&w1 range:NSMakeRange(0, 1)];
        [data getBytes:&w2 range:NSMakeRange(1, 1)];
        short w = w1 + (w2 << 8);
        short h1 = 0, h2 = 0;
        [data getBytes:&h1 range:NSMakeRange(2, 1)];
        [data getBytes:&h2 range:NSMakeRange(3, 1)];
        short h = h1 + (h2 << 8);
        return CGSizeMake(w, h);
    }
    return CGSizeZero;
}
+(CGSize)downloadJPGImageSizeWithRequest:(NSMutableURLRequest*)request
{
    [request setValue:@"bytes=0-209" forHTTPHeaderField:@"Range"];
    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
    
    if ([data length] <= 0x58) {
        return CGSizeZero;
    }
    
    if ([data length] < 210) {// 肯定只有一个DQT字段
        short w1 = 0, w2 = 0;
        [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];
        [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];
        short w = (w1 << 8) + w2;
        short h1 = 0, h2 = 0;
        [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];
        [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];
        short h = (h1 << 8) + h2;
        return CGSizeMake(w, h);
    } else {
        short word = 0x0;
        [data getBytes:&word range:NSMakeRange(0x15, 0x1)];
        if (word == 0xdb) {
            [data getBytes:&word range:NSMakeRange(0x5a, 0x1)];
            if (word == 0xdb) {// 两个DQT字段
                short w1 = 0, w2 = 0;
                [data getBytes:&w1 range:NSMakeRange(0xa5, 0x1)];
                [data getBytes:&w2 range:NSMakeRange(0xa6, 0x1)];
                short w = (w1 << 8) + w2;
                short h1 = 0, h2 = 0;
                [data getBytes:&h1 range:NSMakeRange(0xa3, 0x1)];
                [data getBytes:&h2 range:NSMakeRange(0xa4, 0x1)];
                short h = (h1 << 8) + h2;
                return CGSizeMake(w, h);
            } else {// 一个DQT字段
                short w1 = 0, w2 = 0;
                [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];
                [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];
                short w = (w1 << 8) + w2;
                short h1 = 0, h2 = 0;
                [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];
                [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];
                short h = (h1 << 8) + h2;
                return CGSizeMake(w, h);
            }
        } else {
            return CGSizeZero;
        }
    }
}

@end

2,封装一个使用的方法,可以放在工具类里面 也可以写在当前类

+ (CGRect)cutImage:(NSURL *)imageUrl WithWide:(CGFloat)imageWide height:(CGFloat)imageHeight{
    
    CGSize aWidth=[Single downloadImageSizeWithURL:imageUrl];
    float width=aWidth.width;
    float height=aWidth.height;
    float imgwidth;
    float imgheight;
    float scales=width/height;
    if (width/height>imageWide/imageHeight)
    {
        imgheight=imageHeight;
        imgwidth=imageHeight*scales;
    }else
    {
        imgwidth=imageWide;
        imgheight=imageWide/scales;
    }
    CGRect rect = CGRectMake(0, 0, imgwidth, imgheight);
    return rect;
}

3,使用方法

//imageUrl 需要截取的路径;
//imageWide 显示image的iamgeView的宽 ;
//imageHeight 显示image的iamgeview的高 ;

注意1.需要设置显示imageview的center 

     2.需要clipsToBounds

UIImageView *topImageViw = [[UIImageView alloc] initWithFrame:CGRectMake(i*WINDOW_WIDTH, 0, WINDOW_WIDTH, scrollView.frame.size.height)];
        topImageViw.bounds=[TncTool cutImage:[NSURL URLWithString:self.iamgeUrl] WithWide:WINDOW_WIDTH height:scrollView.frame.size.height];
        topImageViw.center = CGPointMake(WINDOW_WIDTH/2, scrollView.frame.size.height/2);
        topImageViw.clipsToBounds = YES;
        [topImageViw sd_setImageWithURL:[NSURL URLWithString:self.oriArr[i]] placeholderImage:[UIImage imageNamed:PLACEHOLDER]];
        [scrollView addSubview:topImageViw];

至此,凑合着可以使用了.....