UIGraphicsBeginImageContext(self.view.bounds.size);     //currentView 当前的view  创建一个基于位图的图形上下文并指定大小为  
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];//renderInContext呈现接受者及其子范围到指定的上下文  
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();//返回一个基于当前图形上下文的图片     
UIGraphicsEndImageContext();//移除栈顶的基于当前位图的图形上下文    
UIImageWriteToSavedPhotosAlbum(viewImage, nil, nil, nil);//然后将该图片保存到图片图

或者：

+ (UIImage *)captureImageFromView:(UIView *)view {
    CGRect screenRect = [view bounds];
    UIGraphicsBeginImageContextWithOptions(screenRect.size, NO, [UIScreen mainScreen].scale);
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    [view.layer renderInContext:ctx];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}