【iOS开发笔记24/50】调整UIImage的大小

对UIImage调整大小，不知道苹果的API里为什么不提供？

//

//  ImageExtras.h

//

#import <Foundation/Foundation.h>

@interface UIImage (Extras) 

  

- (UIImage *)imageByScalingToSize:(CGSize)targetSize; 

@end

//

//  ImageExtras.m

// 

// 摘自下面的论坛

// http://www.iphonedevsdk.com/forum/iphone-sdk-development/7307-resizing-photo-new-uiimage-2.html

//

#import "ImageExtras.h"

@implementation  UIImage (Extras) 

- (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); 

    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 ; 

}

@end