网络获取图片大小自适应

首先创建一个UIImage类别，如下：

@interface UIImage(UIImageScale) 
-(UIImage*)getSubImage:(CGRect)rect; 
-(UIImage*)scaleToSize:(CGSize)size; 
@end 
  
@implementation UIImage(UIImageScale) 
  
//截取部分图像 
-(UIImage*)getSubImage:(CGRect)rect 
{ 
    CGImageRef subImageRef = CGImageCreateWithImageInRect(self.CGImage, rect); 
    CGRect smallBounds = CGRectMake(0, 0, CGImageGetWidth(subImageRef), CGImageGetHeight(subImageRef)); 
     
    UIGraphicsBeginImageContext(smallBounds.size); 
    CGContextRef context = UIGraphicsGetCurrentContext(); 
    CGContextDrawImage(context, smallBounds, subImageRef); 
    UIImage* smallImage = [UIImage imageWithCGImage:subImageRef]; 
    UIGraphicsEndImageContext(); 
     
    return smallImage; 
} 
  
//等比例缩放 
-(UIImage*)scaleToSize:(CGSize)size  
{ 
    CGFloat width = CGImageGetWidth(self.CGImage); 
    CGFloat height = CGImageGetHeight(self.CGImage); 
     
    float verticalRadio = size.height*1.0/height;  
    float horizontalRadio = size.width*1.0/width; 
     
    float radio = 1; 
    if(verticalRadio>1 && horizontalRadio>1) 
    { 
        radio = verticalRadio > horizontalRadio ? horizontalRadio : verticalRadio;    
    } 
    else 
    { 
        radio = verticalRadio < horizontalRadio ? verticalRadio : horizontalRadio;    
    } 
     
    width = width*radio; 
    height = height*radio; 
     
    int xPos = (size.width - width)/2; 
    int yPos = (size.height-height)/2; 
     
    // 创建一个bitmap的context   
    // 并把它设置成为当前正在使用的context   
    UIGraphicsBeginImageContext(size);   
     
    // 绘制改变大小的图片   
    [self drawInRect:CGRectMake(xPos, yPos, width, height)];   
     
    // 从当前context中创建一个改变大小后的图片   
    UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();   
     
    // 使当前的context出堆栈   
    UIGraphicsEndImageContext();   
     
    // 返回新的改变大小后的图片   
    return scaledImage; 
} 
@end 


然后在下面方法里面调用就可以了！

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://img21.mtime.cn/mg/2011/09/24/112524.53149978.jpg"]] ];
   
   
    // 裁剪图片
    //image = [image getSubImage:CGRectMake(10, 10, 70, 80)];
   
    //等比列缩放
   
    image = [image scaleToSize:CGSizeMake(200, 300)];
   
    UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
   
    [self.window addSubview:imageView];
   
    NSLog(@"image.size:%@",NSStringFromCGSize(CGSizeMake(imageView.image.size.width, imageView.image.size.height)));   //打印获取的网络图片的宽度和高度
   
    [self.window makeKeyAndVisible];
    return YES;
}


//--------------截取部分图片到指定位置-------------------------

图片(UIImage*) img
要截取的起始坐标sx:(int) sx1 sy:(int)sy1
要截取的长度和宽度sw:(int) sw1 sh:(int) sh1
最终要显示的坐标desx:(int) desx1 desy:(int)desy1

-(UIImage*)objectiveDrawRegion:(UIImage*) img sx:(int) sx1 sy:(int)sy1 sw:(int) sw1 sh:(int) sh1 desx:(int) desx1 desy:(int)desy1{
[self saveImage:img name:@"objectiveDrawRegion1.png"];

//创建图片缓冲
void *imageDataRegion=malloc(screenWidth*screenHeight*32);
CGColorSpaceRef iColorSpaceRegion=CGColorSpaceCreateDeviceRGB();
    CGContextRefiDeviceRegion=CGBitmapContextCreate(imageDataRegion,screenWidth,screenHeight,8,4*screenWidth,iColorSpaceRegion,kCGImageAlphaPremultipliedLast);



//剪切区域
    CGRect clipRegion=CGRectMake(sx1,sy1,sw1,sh1);
    CGContextClipToRect(iDeviceRegion, clipRegion);
   
    CGFloat widthf=img.size.width;
    CGFloat heightf=img.size.height;

CGRect  cg=CGRectMake(0.0, 0.0, widthf, heightf);
//画底图
    CGContextDrawImage(iDeviceRegion,cg, img.CGImage);

//将缓冲形成图片
    CGImageRef ioffRegion=CGBitmapContextCreateImage(iDeviceRegion);
 
CGRect  cg1=CGRectMake(desx1, desy1, sw1, sh1);
UIImage *ui=[UIImage imageWithCGImage:ioffRegion];

CGContextDrawImage(当前context,cg1, ui.CGImage);


//清除缓冲
   CGColorSpaceRelease(iColorSpaceRegion);
   CGContextRelease(iDeviceRegion);
   CGImageRelease(ioffRegion);
   free(imageDataRegion);
//    iDeviceRegion=NULL;
//    imageDataRegion=0;

return ui;
}