+ (UIImage *)imageFromView : (UIView *)view
{
//创建一个基于位图的图形上下文并指定大小为CGSizeMake(300,500)
UIGraphicsBeginImageContext(CGSizeMake(90,90));
//renderInContext 呈现接受者及其子范围到指定的上下文
[view.layerrenderInContext:UIGraphicsGetCurrentContext()];
//返回一个基于当前图形上下文的图片
UIImage *extractImage =UIGraphicsGetImageFromCurrentImageContext();
//移除栈顶的基于当前位图的图形上下文
UIGraphicsEndImageContext();
//以png格式返回指定图片的数据
NSData *imageData = UIImagePNGRepresentation(extractImage);
UIImage *imge = [UIImageimageWithData:imageData];
return imge;
}