【代碼筆記】根據size截取屏幕中間矩形區域

代碼：

RootViewController.m

#import "RootViewController.h"

@interface RootViewController ()

@end

@implementation RootViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    //初始化界面
    [self addView];
    
}
#pragma -mark -functions
//初始化界面
-(void)addView
{
    UIImageView *imageView=[[UIImageView alloc]initWithFrame:CGRectMake(50, 100, 200, 200)];
    imageView.backgroundColor=[UIColor redColor];
    //顯示截取的圖
    imageView.image=[self cutCenterImage:[UIImage imageNamed:@"1.jpg"] size:CGSizeMake(200, 200)];
    [self.view addSubview:imageView];
}
#pragma mark 根據size截取圖片中間矩形區域的圖片 這裡的size是正方形
-(UIImage *)cutCenterImage:(UIImage *)image size:(CGSize)size{
    CGSize imageSize = image.size;
    CGRect rect;
    //根據圖片的大小計算出圖片中間矩形區域的位置與大小
    if (imageSize.width > imageSize.height) {
        float leftMargin = (imageSize.width - imageSize.height) * 0.5;
        rect = CGRectMake(leftMargin, 0, imageSize.height, imageSize.height);
    }else{
        float topMargin = (imageSize.height - imageSize.width) * 0.5;
        rect = CGRectMake(0, topMargin, imageSize.width, imageSize.width);
    }
    
    CGImageRef imageRef = image.CGImage;
    //截取中間區域矩形圖片
    CGImageRef imageRefRect = CGImageCreateWithImageInRect(imageRef, rect);
    
    UIImage *tmp = [[UIImage alloc] initWithCGImage:imageRefRect];
    CGImageRelease(imageRefRect);
    
    UIGraphicsBeginImageContext(size);
    CGRect rectDraw = CGRectMake(0, 0, size.width, size.height);
    [tmp drawInRect:rectDraw];
    // 從當前context中創建一個改變大小後的圖片
    tmp = UIGraphicsGetImageFromCurrentImageContext();
    
    // 使當前的context出堆棧
    UIGraphicsEndImageContext();
    
    return tmp;
}
- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}