给界面上任何控件截图并保存为PNG的方法（支持retina高分）

额，发现论坛里的方法老了，我搬个支持retina的方法过来，其实只多没几行～
应该同样能实现截屏的功能～（经过后面网友提醒，看来截屏时无法截取Status Bar的部分）

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UIView *view = [[[[[UIApplication sharedApplication] windows] objectAtIndex:1] subviews] lastObject];//获得某个window的某个subView   NSInteger index = 0;//用来给保存的png命名 for (UIView *subView in [view subviews]) {//遍历这个view的subViews     if ([subView isKindOfClass:NSClassFromString(@"UIImageView")] || [subView isKindOfClass:NSClassFromString(@"UIThreePartButton")]) {//找到自己需要的subView         //支持retina高分的关键         if(UIGraphicsBeginImageContextWithOptions != NULL)         {             UIGraphicsBeginImageContextWithOptions(subView.frame.size, NO, 0.0);         } else {             UIGraphicsBeginImageContext(subView.frame.size);         }                              //获取图像         [subView.layer renderInContext:UIGraphicsGetCurrentContext()];         UIImage *image = UIGraphicsGetImageFromCurrentImageContext();         UIGraphicsEndImageContext();                   //保存图像         NSString *path = [NSHomeDirectory() stringByAppendingFormat:@"/%d.png",index];         if ([UIImagePNGRepresentation(image) writeToFile:path atomically:YES]) {             index += 1;             NSLog(@"Succeeded!");         }         else {             NSLog(@"Failed!");         }     } }