iOS 修改UIImage大小

在iOS中，uiimage没有用于修改大小的属性，要在代码中改变uiimage图片的大小，需要扩展UIImage类，如下：

头文件：

#import 

@interface UIImage (UIImageExtras)

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

@end

.m文件

#import "UIImage+UIImageExtras.h"

@implementation UIImage (UIImageExtras)

- (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