問題描述

我想創建一個 UITableView 或 UIScrollView 的子類，當內容偏移量大于 0 時，它會在頂部有一些陰影，表示內容是可滾動的.(見附圖)

I want to create a subclass of UITableView or UIScrollView that will have some shading at the top when the content offset is > 0 to indicate that the content is scrollable. (See image attached)

我現在實現它的方式是使用 UIViewController，它是 tableView 的委托.我只是在 tableView 頂部有一個 GradientView，然后截取 scrollViewDidScroll: 以動畫化頂部漸變的可見性.

The way I'm implementing it right now is using the UIViewController that is the delegate of the tableView. I simply have a GradientView on top of the tableView, and I intercept scrollViewDidScroll: to animate the visibility of that top gradient.

我對這個實現的問題是它不是干凈的".我希望我的 UIViewControllers 處理邏輯，而不是處理應用漸變和其他東西.我希望我可以刪除一個 UITableView 的子類，它會為我做到這一點.

My problem with this implementation is that it's not "clean". I want my UIViewControllers to take care of logic, and not to deal with applying gradients and stuff. I wish I could just drop a subclass of UITableView that will do that for me.

我面臨的挑戰是我無法弄清楚 tableView 如何在可滾動內容之上添加一個固定內容.

The challenge for me is that I can't figure out how the tableView could add to itself a fixed content on top of the scrollable content.

另一個問題是我應該重寫 UIScrollView 的什么方法來攔截滾動事件.顯然我不希望 tableView 成為自己的代表......

Another question is what method/s of UIScrollView should I override to intercept the scrolling event. Obviously I don't want the tableView to be the delegate of itself...

有什么想法嗎?

謝謝！

推薦答案

好的，我在 Apple 的 WWDC 2011 Session 104 video - Advanced Scroll View Techniques 中找到了解決方案.

Ok, so I found the solution on Apple's WWDC 2011 Session 104 video - Advanced Scroll View Techniques.

此視頻中有一個完整的部分是關于滾動視圖中的固定視圖".根據 Apple 的說法，這里的方法是覆蓋 layoutSubviews 并將所有代碼放在那里以放置您想要的任何位置 - 任何您想要的位置.

There is a whole section in this video about "Stationary Views" inside a scroll view. According to Apple, the way to go here is to override layoutSubviews and put there all the code to position whatever you want - wherever you want.

我試過了，它實際上很簡單，并且按預期工作.

I tried it and it's actually pretty easy and it's working as expected.

例如，如果我想在滾動內容時在表格頂部有一個陰影標題，這就是我應該編寫的代碼:

So for example if I would like a shadowed header on top of the table when the content is being scrolled, this is the code I should write:

-(void) layoutSubviews
{
    [super layoutSubviews];
    [self positionTopShadow];
}

-(void) positionTopShadow
{
    CGFloat yOffset = self.contentOffset.y;
    // I'm doing some limiting so that the maximum height of the shadow view will be 40 pixels
    yOffset = MIN(yOffset, 40);
    yOffset = MAX(0, yOffset);

    CGRect frame = self.topShadowView.frame;
    // The origin should be exactly like the content offset so it would look like
    // the shadow is at the top of the table (when it's actually just part of the content) 
    frame.origin = CGPointMake(0, self.contentOffset.y);
    frame.size.height = yOffset;
    frame.size.width = self.frame.size.width;
    self.topShadowView.frame = frame;

    if (self.topShadowView.superview == nil)
    {
        [self addSubview:self.topShadowView];
    }
    [self bringSubviewToFront:self.topShadowView];
}

這篇關于是否可以將固定內容添加到 UIScrollView?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！