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<UIKit/UIKit.h>

@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 - 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

 

写好扩展类之后，就在要修改UIImage大小的viewcontroller.h头文件空先导入你的写好的扩展类，我的是#import “UIImage+UIImageExtras.h”

这样，你就可以调用你对UIImage写的那个扩展方法了。

我调用的地方

UIImage *tabbarimage=[UIImageimageNamed:@"xxx.png"];

CGSize imagesize=CGSizeMake(50.0, 50.0);

self.tabBarItem.image=[tabbarimageimageByScalingToSize:imagesize];