去掉UIWebView的底图， 右侧的滚动条， 上下滚动出边界时的黑色的图片

    _emailWebView.backgroundColor=[UIColor clearColor]; 
    for (UIView *subView in [_emailWebView subviews])  
    { 
        if ([subView isKindOfClass:[UIScrollView class]])  
        { 
            ((UIScrollView *)subView).bounces = NO; //去掉UIWebView的底图 
//            [(UIScrollView *)_aView setShowsVerticalScrollIndicator:NO]; //右侧的滚动条 
            
            for (UIView *scrollview in subView.subviews)  
            { 
                if ([scrollview isKindOfClass:[UIImageView class]]) 
                { 
                    scrollview.hidden = YES;  //上下滚动出边界时的黑色的图片 
                } 
            } 
        } 
    }