iphone - 获取特定标签栏项目的框架

Question

有没有办法在 UITabBar 中找到特定 UITabBarItem 的框架？

具体来说，我想创建一个图像“落入”其中一个选项卡的动画，类似于例如在邮件中删除电子邮件，或在 iTunes 应用程序中购买轨道。所以我需要动画的目标坐标。

据我所知，没有公共(public) API 来获取坐标，但我很乐意在这一点上弄错。除此之外，我将不得不使用给定选项卡相对于选项卡栏框架的索引来猜测坐标。

Answer 1

Imre 的实现缺少几个恕我直言的重要细节。

1. UITabBarButton View 不一定按顺序排列。例如，如果您在 iPhone 上有超过 5 个选项卡并且重新排列了选项卡，则 View 可能会乱序。
2. 如果您使用超过 5 个选项卡，则越界索引仅表示该选项卡在“更多”选项卡后面。在这种情况下，没有理由使用断言失败，只需使用最后一个选项卡的框架即可。

所以我稍微修改了他的代码，然后我想出了这个:

+ (CGRect)frameForTabInTabBar:(UITabBar*)tabBar withIndex:(NSUInteger)index
{
    NSMutableArray *tabBarItems = [NSMutableArray arrayWithCapacity:[tabBar.items count]];
    for (UIView *view in tabBar.subviews) {
        if ([view isKindOfClass:NSClassFromString(@"UITabBarButton")] && [view respondsToSelector:@selector(frame)]) {
            // check for the selector -frame to prevent crashes in the very unlikely case that in the future
            // objects thar don't implement -frame can be subViews of an UIView
            [tabBarItems addObject:view];
        }
    }
    if ([tabBarItems count] == 0) {
        // no tabBarItems means either no UITabBarButtons were in the subView, or none responded to -frame
        // return CGRectZero to indicate that we couldn't figure out the frame
        return CGRectZero;
    }

    // sort by origin.x of the frame because the items are not necessarily in the correct order
    [tabBarItems sortUsingComparator:^NSComparisonResult(UIView *view1, UIView *view2) {
        if (view1.frame.origin.x < view2.frame.origin.x) {
            return NSOrderedAscending;
        }
        if (view1.frame.origin.x > view2.frame.origin.x) {
            return NSOrderedDescending;
        }
        NSAssert(NO, @"%@ and %@ share the same origin.x. This should never happen and indicates a substantial change in the framework that renders this method useless.", view1, view2);
        return NSOrderedSame;
    }];

    CGRect frame = CGRectZero;
    if (index < [tabBarItems count]) {
        // viewController is in a regular tab
        UIView *tabView = tabBarItems[index];
        if ([tabView respondsToSelector:@selector(frame)]) {
            frame = tabView.frame;
        }
    }
    else {
        // our target viewController is inside the "more" tab
        UIView *tabView = [tabBarItems lastObject];
        if ([tabView respondsToSelector:@selector(frame)]) {
            frame = tabView.frame;
        }
    }
    return frame;
}