优雅处理UIImage图片旋转

UIImag构造方式

UIImag构造方式大致有4种方式

从本地bundle中加载 imageNamed:，传入一个bundle的文件名即可
从本地一个文件路径读取 imageWithContentsOfFile:，需要传一个文件的文件路径path
通过二进制数据NSData来创建imageWithData:
通过一个CoreGraphics的CGImageRef来创建，initWithCGImage:
通过一个CoreImage的CIImage来创建initWithCIImage

通过查阅Apple官网文档我们发现有2个这样的方法，今天就来一探究竟

+ (UIImage *)imageWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(4_0);
+ (UIImage *)imageWithCIImage:(CIImage *)ciImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(6_0);

- (instancetype)initWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(4_0);
- (instancetype)initWithCIImage:(CIImage *)ciImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(6_0);

2个类方法2个实例方法都是类似，这里以CGImageRef为例

+ (UIImage *)imageWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(4_0);

新建的Xcode工程选择single Application
在storyboard中拖一个UIImageView设置它水平垂直居中对齐，宽带高度随便设一个值不要太大就行，设置UIImageView的contentMode为Aspect Fit方便查看以免变形
在UIImageView下发放一个UIButton控件方便后面好对图片进行旋转操作
在viewController中建立一个UIImageView引用,拉出一个rotate按钮的IBAction

现在大概界面大概这样

下面我们实现 - (IBAction)rotateImage:(id)sender {}这个方法

在这里我们想通过点击按钮实现图片旋转为了方便使用我们使用Category的方式实现新建一个UIImage的分类取名叫Rotate

这里需要传一张要处理的图片和一个待处理成的图片方向

+ (UIImage *)rotateImage:(UIImage *)oldImage
         orientation:(UIImageOrientation)orientation;

+ (UIImage *)rotateImage:(UIImage *)oldImage orientation:(UIImageOrientation)orientation{

UIImage *newImage = [UIImage imageWithCGImage:oldImage.CGImage scale:1 orientation:orientation];

NSString *orientationStr = nil;
switch (orientation) {
    case UIImageOrientationUp: {
        orientationStr = @"UIImageOrientationUp";
        break;
    }
    case UIImageOrientationDown: {
        orientationStr = @"UIImageOrientationDown";
        break;
    }
    case UIImageOrientationLeft: {
        orientationStr = @"UIImageOrientationLeft";
        break;
    }
    case UIImageOrientationRight: {
        orientationStr = @"UIImageOrientationRight";
        break;
    }
    case UIImageOrientationUpMirrored: {
        orientationStr = @"UIImageOrientationUpMirrored";
        break;
    }
    case UIImageOrientationDownMirrored: {
        orientationStr = @"UIImageOrientationDownMirrored";
        break;
    }
    case UIImageOrientationLeftMirrored: {
        orientationStr = @"UIImageOrientationLeftMirrored";
        break;
    }
    case UIImageOrientationRightMirrored: {
        orientationStr = @"UIImageOrientationRightMirrored";
        break;
    }

}

NSLog(@"current orientation: %@",orientationStr);

return newImage;

} ```

在button点击事件触发时的这样使用

- (IBAction)rotateImage:(id)sender {

    UIImage *oldImage = self.imgView.image;

    UIImage *rotatedImage = [UIImage rotateImage:oldImage orientation:UIImageOrientationLeft];

    self.imgView.image = rotatedImage;
}

点击按钮测试发现第一次没问题，但是重逢点击无效原来+ (UIImage *)imageWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation方法执行原理是执行前通过 @property(nonatomic,readonly) UIImageOrientation imageOrientation;接口先判断当前图片的方向是否为将要旋转的方向，如果是就直接返回不做处理，如果不是再作旋转处理，也就是说这个方法并没有实际上旋转image的数据，只是用一个枚举标记旋转的状态

如果我们想每次旋转需要直接改变原始image的数据该怎么办呢？在这里我们通过CGBitmapContext,使用CGContextRotateCTM来设置旋转，再把UIImage通过drawInRect 重新绘制出来，通过UIGraphicsGetImageFromCurrentImageContext获得处理后的图片下面是具体实现

- (UIImage *)fixedRotation{
    if (self.imageOrientation == UIImageOrientationUp) return self;
    CGAffineTransform transform = CGAffineTransformIdentity;

    switch (self.imageOrientation) {
        case UIImageOrientationDown:
        case UIImageOrientationDownMirrored:
            transform = CGAffineTransformTranslate(transform, self.size.width, self.size.height);
            transform = CGAffineTransformRotate(transform, M_PI);
            break;

        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
            transform = CGAffineTransformTranslate(transform, self.size.width, 0);
            transform = CGAffineTransformRotate(transform, M_PI_2);
            break;

        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            transform = CGAffineTransformTranslate(transform, 0, self.size.height);
            transform = CGAffineTransformRotate(transform, -M_PI_2);
            break;
        case UIImageOrientationUp:
        case UIImageOrientationUpMirrored:
            break;
    }

    switch (self.imageOrientation) {
        case UIImageOrientationUpMirrored:
        case UIImageOrientationDownMirrored:
            transform = CGAffineTransformTranslate(transform, self.size.width, 0);
            transform = CGAffineTransformScale(transform, -1, 1);
            break;

        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRightMirrored:
            transform = CGAffineTransformTranslate(transform, self.size.height, 0);
            transform = CGAffineTransformScale(transform, -1, 1);
            break;
        case UIImageOrientationUp:
        case UIImageOrientationDown:
        case UIImageOrientationLeft:
        case UIImageOrientationRight:
            break;
    }

    // Now we draw the underlying CGImage into a new context, applying the transform
    // calculated above.
    CGContextRef ctx = CGBitmapContextCreate(NULL, self.size.width, self.size.height,
                                             CGImageGetBitsPerComponent(self.CGImage), 0,
                                             CGImageGetColorSpace(self.CGImage),
                                             CGImageGetBitmapInfo(self.CGImage));
    CGContextConcatCTM(ctx, transform);
    switch (self.imageOrientation) {
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            // Grr...
            CGContextDrawImage(ctx, CGRectMake(0,0,self.size.height,self.size.width), self.CGImage);
            break;

        default:
            CGContextDrawImage(ctx, CGRectMake(0,0,self.size.width,self.size.height), self.CGImage);
            break;
    }

    // And now we just create a new UIImage from the drawing context
    CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
    UIImage *img = [UIImage imageWithCGImage:cgimg];
    CGContextRelease(ctx);
    CGImageRelease(cgimg);
    return img;

}

现在再优化一下原来+ (UIImage *)rotateImage:(UIImage *)oldImage orientation:(UIImageOrientation)orientation 方法,修改成这样

+ (UIImage *)rotateImage:(UIImage *)oldImage orientation:(UIImageOrientation)orientation{

    UIImage *newImage = [UIImage imageWithCGImage:oldImage.CGImage scale:1 orientation:orientation];

    //fix original Image with gived orientation.
    UIImage *fixedRotationImage = [newImage fixedRotation];

    NSString *orientationStr = nil;
    switch (orientation) {
        case UIImageOrientationUp: {
            orientationStr = @"UIImageOrientationUp";
            break;
        }
        case UIImageOrientationDown: {
            orientationStr = @"UIImageOrientationDown";
            break;
        }
        case UIImageOrientationLeft: {
            orientationStr = @"UIImageOrientationLeft";
            break;
        }
        case UIImageOrientationRight: {
            orientationStr = @"UIImageOrientationRight";
            break;
        }
        case UIImageOrientationUpMirrored: {
            orientationStr = @"UIImageOrientationUpMirrored";
            break;
        }
        case UIImageOrientationDownMirrored: {
            orientationStr = @"UIImageOrientationDownMirrored";
            break;
        }
        case UIImageOrientationLeftMirrored: {
            orientationStr = @"UIImageOrientationLeftMirrored";
            break;
        }
        case UIImageOrientationRightMirrored: {
            orientationStr = @"UIImageOrientationRightMirrored";
            break;
        }

    }

    NSLog(@"current orientation: %@",orientationStr);

    return fixedRotationImage;
}

现在再测试一下，well，It‘s OK。

have fun!!!

参考资料：

Apple-UIImage Class Reference
ios-uiimageview-how-to-handle-uiimage-image-orientation
UIImageOrientation / EXIF orientation sample images

备注：欢迎转载，但请一定注明出处！ https://github.com/wangruofeng/Github_Blog

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