在哪里可以指定哪个 UIView 用于 UIViewController 的 view 属性？

发布于 2024-10-16 05:08:52 字数 263 浏览 3 评论 0原文

我想在运行时设置 UIViewController 的视图属性。我有一个包含两个视图的 .xib 文件，我希望拥有 .xib 文件的 UIViewController 子类决定在运行时使用哪个 UIView。我以为我可以在 loadView 中通过说来做到这一点，

if(some condition)
    self.view = thisView;
else
    self.view = thatView;

但那不起作用。我该怎么做？

原文

I want to set the view property of a UIViewController at runtime. I have an .xib file with two views, and I want my UIViewController subclass that owns the .xib file to decide which UIView to use at runtime. I thought I could do this in loadView by just saying

if(some condition)
    self.view = thisView;
else
    self.view = thatView;

but that didn't work. How can I do this?

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ぇ气 2024-10-23 05:08:52

如果您想动态选择视图，请将其设置在 -[UIViewController loadView] 中。不过需要注意的是：如果视图尚未加载，调用 -[UIViewController view] 将会调用 -[UIViewController loadView]，所以如果你这样做

-(void)loadView
{
    self.view = [[[UIView alloc] initWithFrame:CGRectZero] autorelease];
    self.view.backgroundColor = [UIColor redColor];
}

：该方法的第二行将调用 -loadView，您将获得无限递归（这将导致堆栈溢出和崩溃）。您需要设置视图，然后在设置后设置 .view 属性，如下所示：

-(void)loadView
{
    UIView *newView =  [[[UIView alloc] initWithFrame:CGRectZero] autorelease];
    newView.backgroundColor = [UIColor redColor];

    self.view = newView;
}

因此您可能需要执行如下操作：

-(void)loadView
{
    UIView *newView = nil;

    if (self.theSkyIsBlue) {
        newView = [[[BlueSkyView alloc] initWithFrame:CGRectZero] autorelease];
        newView.backgroundColor = [UIColor blueColor];
    }
    else {
        newView = [[[GraySkyView alloc] initWithFrame:CGRectZero] autorelease];
        newView.backgroundColor = [UIColor grayColor];
    }

    self.view = newView;
}

附录 1 - 更新展示如何对 XIB 中定义的不同视图使用容器视图

如果您想引用 XIB 中的其他内容，更好的方法是使用 .view 作为其他视图的“容器视图”。在 -viewDidLoad 中进行设置，如下所示：

- (void)viewDidLoad
{
    UIView *childView = nil;
    if (someCondition) {
        childView = self.blueView;
    }
    else {
        childView = self.grayView;
    }
    [self.view addSubview:childView];
    childView.frame = self.view.bounds;
}

请注意，如果您想稍后交换视图，则应该将 childView 设为属性，而不是局部变量，因此您可以在插入新的 childView 时删除旧的 childView。

If you want to choose your view dynamically, set it inside -[UIViewController loadView]. A word of caution though: calling -[UIViewController view] will call -[UIViewController loadView] if the view hasn't been loaded yet, so if you do this:

-(void)loadView
{
    self.view = [[[UIView alloc] initWithFrame:CGRectZero] autorelease];
    self.view.backgroundColor = [UIColor redColor];
}

The second line of that method will call -loadView, and you'll get infinite recursion (which will lead to a stack overflow, and a crash). You need to setup your view, then set the .view property when you've set it up, like this:

-(void)loadView
{
    UIView *newView =  [[[UIView alloc] initWithFrame:CGRectZero] autorelease];
    newView.backgroundColor = [UIColor redColor];

    self.view = newView;
}

So you'll probably want to do something like this:

-(void)loadView
{
    UIView *newView = nil;

    if (self.theSkyIsBlue) {
        newView = [[[BlueSkyView alloc] initWithFrame:CGRectZero] autorelease];
        newView.backgroundColor = [UIColor blueColor];
    }
    else {
        newView = [[[GraySkyView alloc] initWithFrame:CGRectZero] autorelease];
        newView.backgroundColor = [UIColor grayColor];
    }

    self.view = newView;
}

Addendum 1 - update to show how to use a container view for different views defined in a XIB

If you want to reference other stuff in your XIB, a better approach is to use your .view as a "container view" for your other views. Set it up in -viewDidLoad, like this:

- (void)viewDidLoad
{
    UIView *childView = nil;
    if (someCondition) {
        childView = self.blueView;
    }
    else {
        childView = self.grayView;
    }
    [self.view addSubview:childView];
    childView.frame = self.view.bounds;
}

Note that if you want to swap your views later on, you should make childView a property, instead of a local variable, so you can remove the old childView when inserting a new one.

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