IOS 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=[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

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