缩放图片并截图中间位置显示

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    [self addView];
}
#pragma -mark -functions
//主界面
-(void)addView
{
    UIImage *imagePicture=[UIImage imageNamed:@"1.jpg"];
    UIImageView *imageView=[[UIImageView alloc]initWithFrame:CGRectMake(50, 100, 200, 200)];
    imageView.image=[self scaleImage:imagePicture size:CGSizeMake(300, 200)];
    imageView.backgroundColor=[UIColor redColor];
    [self.view addSubview:imageView];
}

//缩放图片，并截取中间位置显示
-(UIImage*)scaleImage:(UIImage *)image size:(CGSize )size{
    CGSize imgSize = image.size; //原图大小
    CGSize viewSize = size;          //视图大小
    CGFloat imgwidth = 0;            //缩放后的图片宽度
    CGFloat imgheight = 0;          //缩放后的图片高度
    
    //视图横长方形及正方形
    if (viewSize.width >= viewSize.height) {
        //缩小
        if (imgSize.width > viewSize.width && imgSize.height > viewSize.height) {
            imgwidth = viewSize.width;
            imgheight = imgSize.height/(imgSize.width/imgwidth);
        }
        //放大
        if(imgSize.width < viewSize.width){
            imgwidth = viewSize.width;
            imgheight = (viewSize.width/imgSize.width)*imgSize.height;
        }
        //判断缩放后的高度是否小于视图高度
        imgheight = imgheight < viewSize.height?viewSize.height:imgheight;
    }
    
    //视图竖长方形
    if (viewSize.width < viewSize.height) {
        //缩小
        if (imgSize.width > viewSize.width && imgSize.height > viewSize.height) {
            imgheight = viewSize.height;
            imgwidth = imgSize.width/(imgSize.height/imgheight);
        }
        
        //放大
        if(imgSize.height < viewSize.height){
            imgheight = viewSize.width;
            imgwidth = (viewSize.height/imgSize.height)*imgSize.width;
        }
        //判断缩放后的高度是否小于视图高度
        imgwidth = imgwidth < viewSize.width?viewSize.width:imgwidth;
    }
    
    //重新绘制图片大小
    UIImage *i;
    UIGraphicsBeginImageContext(CGSizeMake(imgwidth, imgheight));
    [image drawInRect:CGRectMake(0, 0, imgwidth, imgheight)];
    i=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    //截取中间部分图片显示
    if (imgwidth > 0) {
        CGImageRef newImageRef = CGImageCreateWithImageInRect(i.CGImage, CGRectMake((imgwidth-viewSize.width)/2, (imgheight-viewSize.height)/2, viewSize.width, viewSize.height));
        return [UIImage imageWithCGImage:newImageRef];
    }else{
        CGImageRef newImageRef = CGImageCreateWithImageInRect(image.CGImage, CGRectMake((imgwidth-viewSize.width)/2, (imgheight-viewSize.height)/2, viewSize.width, viewSize.height));
        return [UIImage imageWithCGImage:newImageRef];
    }
}