iOS开发>学无止境

最近遇到这样的需求：从服务器获取到一张照片，只需要显示他的左半部分，或者中间部分等等。也就是截取UIImage指定大小区域。

UIImage扩展

我的解决方案是对UIImage进行扩展。通过CGImageRef和CGImage完成截取，调用的方法是：CGImageCreateWithImageInRect。扩展类叫UIImage+Crop，具体代码如下：

UIImage+Crop.h

#import <UIKit/UIKit.h>

typedef NS_ENUM(NSInteger, XYCropImageStyle){
    XYCropImageStyleRight               =0,      // 右半部分
    XYCropImageStyleCenter              =1,      // 中间部分
    XYCropImageStyleLeft                =2,      // 左半部分
    XYCropImageStyleRightOneOfThird     =3,      // 右侧三分之一部分
    XYCropImageStyleCenterOneOfThird    =4,      // 中间三分之一部分
    XYCropImageStyleLeftOneOfThird      =5,      // 左侧三分之一部分
    XYCropImageStyleRightQuarter        =6,      // 右侧四分之一部分
    XYCropImageStyleCenterRightQuarter  =7,      // 中间右侧四分之一部分
    XYCropImageStyleCenterLeftQuarter   =8,      // 中间左侧四分之一部分
    XYCropImageStyleLeftQuarter         =9,      // 左侧四分之一部分
};

@interface UIImage (Crop)
- (UIImage *)imageByCroppingWithStyle:(XYCropImageStyle)style;

@end

UIImage+Crop.m

#import "UIImage+Crop.h"

@implementation UIImage (Crop)

- (UIImage *)imageByCroppingWithStyle:(XYCropImageStyle)style
{
    CGRect rect;
    switch (style) {
        case XYCropImageStyleLeft:
            rect = CGRectMake(0, 0, self.size.width/2, self.size.height);
            break;
        case XYCropImageStyleCenter:
            rect = CGRectMake(self.size.width/4, 0, self.size.width/2, self.size.height);
            break;
        case XYCropImageStyleRight:
            rect = CGRectMake(self.size.width/2, 0, self.size.width/2, self.size.height);
            break;
        case XYCropImageStyleLeftOneOfThird:
            rect = CGRectMake(0, 0, self.size.width/3, self.size.height);
            break;
        case XYCropImageStyleCenterOneOfThird:
            rect = CGRectMake(self.size.width/3, 0, self.size.width/3, self.size.height);
            break;
        case XYCropImageStyleRightOneOfThird:
            rect = CGRectMake(self.size.width/3*2, 0, self.size.width/3, self.size.height);
            break;
        case XYCropImageStyleLeftQuarter:
            rect = CGRectMake(0, 0, self.size.width/4, self.size.height);
            break;
        case XYCropImageStyleCenterLeftQuarter:
            rect = CGRectMake(self.size.width/4, 0, self.size.width/4, self.size.height);
            break;
        case XYCropImageStyleCenterRightQuarter:
            rect = CGRectMake(self.size.width/4*2, 0, self.size.width/4, self.size.height);
            break;
        case XYCropImageStyleRightQuarter:
            rect = CGRectMake(self.size.width/4*3, 0, self.size.width/4, self.size.height);
            break;
        default:
            break;
    }
    CGImageRef imageRef = self.CGImage;
    CGImageRef imagePartRef = CGImageCreateWithImageInRect(imageRef, rect);
    UIImage *cropImage = [UIImage imageWithCGImage:imagePartRef];
    CGImageRelease(imagePartRef);
    return cropImage;
}

实际运用

简单测试一下，看看有没有实现我们想要的效果。首先，先加载一个完整的UIImageView。这个应该不难。代码如下：

UIImageView *imgView = [[UIImageView alloc] init];
imgView.frame = CGRectMake((SCREEN.width - 226) / 2, 100, 226, 106);
UIImage *image = [UIImage imageNamed:@"ganggang"];
imgView.image = image;
[self.view addSubview:imgView];

运行一下：

要对UIImage进行裁剪，首先导入头文件：

#import "UIImage+Crop.h"

在上面UIImage *image = [UIImage imageNamed:@"ganggang"];这段代码之后加上下面这句：

image = [image imageByCroppingWithStyle:XYCropImageStyleLeft];

XYCropImageStyleLeft是截取照片的左半部分。效果如下：

截取成功，还可以截取其他区域的，只需要传入不同的XYCropImageStyle即可实现。以上代码依然在iOSStrongDemo里。