拉伸UIImage

转自：http://stackoverflow.com/questions/2658738/the-simplest-way-to-resize-an-uiimage

- (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {

    UIGraphicsBeginImageContext(newSize);

    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    

    UIGraphicsEndImageContext();

    return newImage;

}