修改UIImage大小

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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=[UIImage imageNamed:@"xxx.png"];

CGSize imagesize=CGSizeMake(50.0, 50.0);

self.tabBarItem.image=[tabbarimage imageByScalingToSize:imagesize];

下面是网上另外一个扩展UIImage类的版本，头文件我就不发了，直接上.m文件

@implementation UIImage (Category)   - (UIImage*)transformWidth:(CGFloat)width                     height:(CGFloat)height {           CGFloat destW = width;     CGFloat destH = height;     CGFloat sourceW = width;     CGFloat sourceH = height;               CGImageRef imageRef = self.CGImage;     CGContextRef bitmap = CGBitmapContextCreate(NULL,                                                 destW,                                                 destH,                                                 CGImageGetBitsPerComponent(imageRef),                                                 4*destW,                                                 CGImageGetColorSpace(imageRef),                                                 (kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst));           CGContextDrawImage(bitmap, CGRectMake(0, 0, sourceW, sourceH), imageRef);           CGImageRef ref = CGBitmapContextCreateImage(bitmap);     UIImage *result = [UIImage imageWithCGImage:ref];     CGContextRelease(bitmap);     CGImageRelease(ref);           return result; } @end