很简单的一个功能，但是长时间不用就忘了，所以放在这里当做笔记好了。

//根据一个View生成一个image
- (UIImage *)screenshotForView:(UIView *)view {
    UIImage *image = nil;
    //判断View类型（一般不是滚动视图或者其子类的话内容不会超过一屏，当然如果超过了也可以通过修改frame来实现绘制）
    if ([view.class isSubclassOfClass:[UIScrollView class]]) {
        UIScrollView *scrView = (UIScrollView *)view;
    
        CGPoint tempContentOffset = scrView.contentOffset;
        CGRect tempFrame = scrView.frame;
    
        scrView.contentOffset = CGPointZero;
        scrView.frame = CGRectMake(0, 0, scrView.contentSize.width, scrView.contentSize.height);
    
        image = [self screenshotForView:scrView size:scrView.frame.size];
   
        scrView.contentOffset = tempContentOffset;
        scrView.frame = tempFrame;
    
    } else {
        image = [self screenshotForView:view size:view.frame.size];
    }

    return image;
}

- (UIImage *)screenshotForView:(UIView *)view size:(CGSize)size {
    UIImage *image = nil;
    UIGraphicsBeginImageContextWithOptions(size, YES, [UIScreen mainScreen].scale);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];

    image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
    return image;
}