UIImage扩展用代码直接改变图片大小

以下内容属于转载

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