可能它在viewDidLoad中不起作用,因为视图不会添加到视图层次结构中。但根据苹果文档becomeFirstResponder应在连接到一个UIWindow对象只叫:
However, you should only call it on that view if it is part of a view hierarchy.
If the view’s window property holds a UIWindow object, it has been installed
in a view hierarchy; if it returns nil, the view is detached from any hierarchy.
所以,我认为,要实现必要的行为,最好的地方是将调用到viewWillAppear
方法。
更新。
因此,在viewWillAppear中控制器的视图尚未连接到一个UIWindow ......它只是通知,该视图将被添加到视图层次
这可能有些棘手,但你可以在viewWillAppear中一些小的延迟:
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
double delayInSeconds = 0.05;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^{
make first responder here
});
}
但我相信这是应该是一个更好的解决方案
你在哪里启动你的搜索栏? – 2013-03-18 08:57:45
您是否尝试将[self.searchBar becomeFirstResponder]放入viewWillAppear?它在viewDidLoad之后调用,但viewController不可见 – Mikhail 2013-03-18 08:58:04
@roronoazorro:我正在使用StoryBoard。 – 2013-03-18 10:20:47