UIImage扩展用代码直接改变图片大小

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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=[UIImageimageNamed:@"xxx.png"];

CGSize imagesize=CGSizeMake(50.0, 50.0);

self.tabBarItem.image=[tabbarimageimageByScalingToSize: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

@implementationUIImage (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);

     

    returnresult;

}

@end