iphone 屏幕截图

- (UIImage*)screenshot  {     

     // Create a graphics context with the target size     

     // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration     

     // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext    

     CGSize imageSize = [[UIScreen mainScreen] bounds].size;     

     if (NULL != UIGraphicsBeginImageContextWithOptions)        

         UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);     

     else         

         UIGraphicsBeginImageContext(imageSize);     

     CGContextRef context = UIGraphicsGetCurrentContext();      

     // Iterate over every window from back to front     

     for (UIWindow *window in [[UIApplication sharedApplication] windows])      {         

         if (![window respondsToSelector:@selector(screen)] || [window screen] == [UIScreen mainScreen])         {             

             // -renderInContext: renders in the coordinate space of the layer,             

             // so we must first apply the layer's geometry to the graphics context             

             CGContextSaveGState(context);             

             // Center the context around the window's anchor point             

             CGContextTranslateCTM(context, [window center].x, [window center].y);             

             // Apply the window's transform about the anchor point            

             CGContextConcatCTM(context, [window transform]);             

             // Offset by the portion of the bounds left of and above the anchor point             

             CGContextTranslateCTM(context, -[window bounds].size.width * [[window layer] anchorPoint].x, 

                                   -[window bounds].size.height * [[window layer] anchorPoint].y);              

             // Render the layer hierarchy to the current context             

             [[window layer] renderInContext:context];              

             // Restore the context            

             CGContextRestoreGState(context);         

         }     

     }  

     

     // Retrieve the screenshot image     

     UIImage *image = UIGraphicsGetImageFromCurrentImageContext();      

     UIGraphicsEndImageContext();      

     return image; 

 }