根据UIImage创建任意大小thumbnail

+ (UIImage*)thumbnailOfImage:(UIImage*)image withSize:(CGSize)aSize{         //NSLog(@"create thumbnail image");                 if (!image)              return nil;                 CGImageRef imageRef = [image CGImage];         UIImage *thumb = nil;                 //   struct CGSize imgSize = [imageRef size];         float _width = CGImageGetWidth(imageRef);         float _height = CGImageGetHeight(imageRef);                 // hardcode width and height for now, shouldn't stay like that         float _resizeToWidth;         float _resizeToHeight;                 _resizeToWidth = aSize.width;         _resizeToHeight = aSize.height;                 float _moveX = 0.0f;         float _moveY = 0.0f;                 // determine the start position in the window if it doesn't fit the sizes 100%         //NSLog(@" width: %f  to: %f", _width, _resizeToWidth);         //NSLog(@" height: %f  to: %f", _height, _resizeToHeight);                 // resize the image if it is bigger than the screen only         if ( (_width > _resizeToWidth) || (_height > _resizeToHeight) )         {              float _amount = 0.0f;                           if (_width > _resizeToWidth)              {                     _amount = _resizeToWidth / _width;                     _width *= _amount;                     _height *= _amount;                     //NSLog(@"1 width: %f height: %f", _width, _height);              }              if (_height > _resizeToHeight)              {                     _amount = _resizeToHeight / _height;                     _width *= _amount;                     _height *= _amount;                     //NSLog(@"2 width: %f height: %f", _width, _height);              }             }                 _width = (NSInteger)_width;         _height = (NSInteger)_height;                 _resizeToWidth = _width;         _resizeToHeight = _height;                 CGContextRef bitmap = CGBitmapContextCreate(                                                                                    NULL,                                                                                    _resizeToWidth,                                                                                    _resizeToHeight,                                                                                    CGImageGetBitsPerComponent(imageRef),                                                                                    CGImageGetBitsPerPixel(imageRef)*_resizeToWidth,                                                                                    CGImageGetColorSpace(imageRef),                                                                                    CGImageGetBitmapInfo(imageRef)                                                                                    );                 // now center the image         _moveX = (_resizeToWidth - _width) / 2;         _moveY = (_resizeToHeight - _height) / 2;                 CGContextSetRGBFillColor(bitmap, 1.f, 1.f, 1.f, 1.0f);         CGContextFillRect( bitmap, CGRectMake(0, 0, _resizeToWidth, _resizeToHeight));         //   CGContextRotateCTM( bitmap, 180*(M_PI/180));         CGContextDrawImage( bitmap, CGRectMake(_moveX, _moveY, _width, _height), imageRef );                 // create a templete imageref.         CGImageRef ref = CGBitmapContextCreateImage( bitmap );         thumb = [UIImage imageWithCGImage:ref];                 // release the templete imageref.         CGContextRelease( bitmap );         CGImageRelease( ref );                 return [[thumb retain] autorelease];}