UIView:如何确定视图是否已存在？

Question

我想知道如何找出子视图(在我的情况下是pageShadowView)是否已添加到我的视图中.

我想出了这个,但它确实不起作用:

if ([pageShadowView isKindOfClass:[self.view class]]) {
        [self.view addSubview:pageShadowView];
    }

而且,我仍然对自我感到困惑.我知道这与明确我们正在谈论当前ViewController的视图有关...但如果(1)没有其他ViewControllers或(2)如果它真的不重要,我真的需要它吗？因为如果我想引用另一个viewController,我一定要调用它吗？

如果这一切都非常基本,我很抱歉,但我非常感谢你的评论.

Answer 1

这里:

BOOL doesContain = [self.view.subviews containsObject:pageShadowView];

是的,你需要这个self.没有明确的ivar"视图" UIViewController.该self.view语句实际上是一个方法调用,[self view]它是一个getter for UIViewControllerview.

Answer 2

给它一个唯一的标签:view.tag = UNIQUE_TAG,然后检查容器视图是否存在:

BOOL alreadyAdded = [containerView viewWithTag:UNIQUE_TAG] != nil;

Answer 3

你可以找到像这样的子视图

for(UIView *view in self.view.subviews)
{
    if([view isKindOfClass:[UIView class]])
    {
        //here do your work
    }
}

Answer 4

在Swift中还有一种方法可以找到:isDescendant(of view: UIView) -> Bool或者在Obj-C中: - (BOOL)isDescendantOfView:(UIView *)view

斯威夫特:

    if myView.isDescendant(of: self.view) {
        //myView is subview of self.view, remove it.
        myView.removeFromSuperview()
    } else {
        //myView is not subview of self.view, add it.
        self.view.addSubview(myView)
    }

Obj-C:

if([myView isDescendantOfView:self.view]) {   
    //myView is subview of self.view, remove it.
    [myView removeFromSuperView];
} else {
    //myView is not subview of self.view, add it.
    [self.view addSubView:myView];
}