转自:http://www.codeios.com/thread-894-1-1.html

这个很有用的 UIImage 扩展之前的帖子：，支持放大和旋转，可在许多 App 中使用。代码：

// //  UIImage-Extensions.h // //  Created by Hardy Macia on 7/1/09. //  Copyright 2009 Catamount Software. All rights reserved. //     #import 
     
       @interface UIImage (CS_Extensions)     - (UIImage *)imageAtRect:(CGRect)rect;     - (UIImage *)imageByScalingProportionallyToMinimumSize:(CGSize)targetSize;     - (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize;     - (UIImage *)imageByScalingToSize:(CGSize)targetSize;     - (UIImage *)imageRotatedByRadians:(CGFloat)radians;     - (UIImage *)imageRotatedByDegrees:(CGFloat)degrees; @end; // //  UIImage-Extensions.m // //  Created by Hardy Macia on 7/1/09. //  Copyright 2009 Catamount Software. All rights reserved. //     #import "UIImage-Extensions.h"     CGFloat DegreesToRadians(CGFloat degrees) {
   return degrees * M_PI / 180;};     CGFloat RadiansToDegrees(CGFloat radians) {
   return radians * 180/M_PI;}; @implementation UIImage (CS_Extensions)     -(UIImage *)imageAtRect:(CGRect)rect     {
          CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], rect);        UIImage* subImage = [UIImage imageWithCGImage: imageRef];        CGImageRelease(imageRef); return subImage;     }     - (UIImage *)imageByScalingProportionallyToMinimumSize:(CGSize)targetSize {
          UIImage *sourceImage = self;        UIImage *newImage = nil;        CGSize imageSize = sourceImage.size;        CGFloat width = imageSize.width;        CGFloat height = imageSize.height;        CGFloat targetWidth = targetSize.width;        CGFloat targetHeight = targetSize.height;        CGFloat scaleFactor = 0.0;        CGFloat scaledWidth = targetWidth;        CGFloat scaledHeight = targetHeight;        CGPoint thumbnailPoint = CGPointMake(0.0,0.0); if (CGSizeEqualToSize(imageSize, targetSize) == NO) {
             CGFloat widthFactor = targetWidth / width;           CGFloat heightFactor = targetHeight / height; if (widthFactor > heightFactor)              scaleFactor = widthFactor; else              scaleFactor = heightFactor;           scaledWidth  = width * scaleFactor;           scaledHeight = height * scaleFactor; // center the image           if (widthFactor > heightFactor) {
                thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;           } else if (widthFactor < heightFactor) {
                thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;           }        } // this is actually the interesting part:              UIGraphicsBeginImageContext(targetSize);        CGRect thumbnailRect = CGRectZero;        thumbnailRect.origin = thumbnailPoint;        thumbnailRect.size.width  = scaledWidth;        thumbnailRect.size.height = scaledHeight;        [sourceImage drawInRect:thumbnailRect];        newImage = UIGraphicsGetImageFromCurrentImageContext();        UIGraphicsEndImageContext(); if(newImage == nil) NSLog(@"could not scale image"); return newImage ;     }     - (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize {
          UIImage *sourceImage = self;        UIImage *newImage = nil;        CGSize imageSize = sourceImage.size;        CGFloat width = imageSize.width;        CGFloat height = imageSize.height;        CGFloat targetWidth = targetSize.width;        CGFloat targetHeight = targetSize.height;        CGFloat scaleFactor = 0.0;        CGFloat scaledWidth = targetWidth;        CGFloat scaledHeight = targetHeight;        CGPoint thumbnailPoint = CGPointMake(0.0,0.0); if (CGSizeEqualToSize(imageSize, targetSize) == NO) {
             CGFloat widthFactor = targetWidth / width;           CGFloat heightFactor = targetHeight / height; if (widthFactor < heightFactor)              scaleFactor = widthFactor; else              scaleFactor = heightFactor;           scaledWidth  = width * scaleFactor;           scaledHeight = height * scaleFactor; // center the image           if (widthFactor < heightFactor) {
                thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;           } else if (widthFactor > heightFactor) {
                thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;           }        } // this is actually the interesting part:              UIGraphicsBeginImageContext(targetSize);        CGRect thumbnailRect = CGRectZero;        thumbnailRect.origin = thumbnailPoint;        thumbnailRect.size.width  = scaledWidth;        thumbnailRect.size.height = scaledHeight;        [sourceImage drawInRect:thumbnailRect];        newImage = UIGraphicsGetImageFromCurrentImageContext();        UIGraphicsEndImageContext(); if(newImage == nil) NSLog(@"could not scale image"); return newImage ;     }     - (UIImage *)imageByScalingToSize:(CGSize)targetSize {
          UIImage *sourceImage = self;        UIImage *newImage = nil; //   CGSize imageSize = sourceImage.size; //   CGFloat width = imageSize.width; //   CGFloat height = imageSize.height;              CGFloat targetWidth = targetSize.width;        CGFloat targetHeight = targetSize.height; //   CGFloat scaleFactor = 0.0;        CGFloat scaledWidth = targetWidth;        CGFloat scaledHeight = targetHeight;        CGPoint thumbnailPoint = CGPointMake(0.0,0.0); // this is actually the interesting part:              UIGraphicsBeginImageContext(targetSize);        CGRect thumbnailRect = CGRectZero;        thumbnailRect.origin = thumbnailPoint;        thumbnailRect.size.width  = scaledWidth;        thumbnailRect.size.height = scaledHeight;        [sourceImage drawInRect:thumbnailRect];        newImage = UIGraphicsGetImageFromCurrentImageContext();        UIGraphicsEndImageContext(); if(newImage == nil) NSLog(@"could not scale image"); return newImage ;     }     - (UIImage *)imageRotatedByRadians:(CGFloat)radians     {
   return [self imageRotatedByDegrees:RadiansToDegrees(radians)];     }     - (UIImage *)imageRotatedByDegrees:(CGFloat)degrees     {  // calculate the size of the rotated view's containing box for our drawing space        UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,self.size.width, self.size.height)];        CGAffineTransform t = CGAffineTransformMakeRotation(DegreesToRadians(degrees));        rotatedViewBox.transform = t;        CGSize rotatedSize = rotatedViewBox.frame.size;        [rotatedViewBox release]; // Create the bitmap context        UIGraphicsBeginImageContext(rotatedSize);        CGContextRef bitmap = UIGraphicsGetCurrentContext(); // Move the origin to the middle of the image so we will rotate and scale around the center.        CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2); //// Rotate the image context        CGContextRotateCTM(bitmap, DegreesToRadians(degrees)); // Now, draw the rotated/scaled image into the context        CGContextScaleCTM(bitmap, 1.0, -1.0);        CGContextDrawImage(bitmap, CGRectMake(-self.size.width / 2, -self.size.height / 2, self.size.width, self.size.height), [self CGImage]);        UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();        UIGraphicsEndImageContext();