cocoa - NSTableView的viewForTableColumn :row: called for more rows than expected in Mavericks

Question

我的理解是 viewForTableColumn:row: 只会针对可见的行调用。

我使用以下内容确认了这一点:NSRange rowsInRect = [aTableView rowsInRect:[aTableViewvisibleRect]];NSInteger lastVisibleRow = rowsInRect.location + rowsInRect.length;

但是对于 Mavericks，viewForTableColumn:row 会在不向下滚动的情况下被调用很多次。

例如，如果我的最后一个可见行是 35，则为 139 行调用数据源方法。

谁能解释一下吗？

Answer 1

我在 OS X v10.9 的 AppKit 发行说明中找到了对此的解释。

这里是:

Mac OS 10.9 has a new feature called Responsive Scrolling. Responsive Scrolling allows the application to continue to rapidly scroll content even when the application’s main thread is busy doing other work. AppKit accomplishes this by having the document view draw more than what is currently visible during idle.

To facilitate Responsive Scrolling, your document view will be asked to draw portions that are not currently visible to the user.

The following method is called by NSView with a 'rect' for a recommended area that should be fully rendered for overdraw. Override this method and bring in additional subviews and pre-cached content for the 'rect' in order to perform responsive scrolling. To suppress overdraw for a particular view (such as NSTableView), override this method and call [super prepareContentInRect:[self visibleRect]].

(void)prepareContentInRect:(NSRect)rect;