当/如何使UITextView成为第一响应者？
UITextView is a subclass of UIView, and it becomes a first responder when the user taps on it or when the app programmatically calls the becomeFirstResponder method on it.
In some cases, the app might need the UITextView to become a first responder programmatically, instead of relying on user interaction. This can be useful in scenarios where the app needs to automatically set focus on a certain text field and open the keyboard.
For example, in a form-based view controller, when the user taps on a "Sign Up" button, the app might push a new view controller with several text fields. To automatically set focus on the first text field and show the keyboard, the app can call the becomeFirstResponder method on that UITextView. This will make it the first responder and open the keyboard for user input.
Here is an example code snippet that demonstrates how to make a UITextView become a first responder:
class MyViewController: UIViewController {
@IBOutlet weak var myTextView: UITextView!
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
myTextView.becomeFirstResponder()
}
}
In this example, the UITextView named "myTextView" becomes a first responder when the view controller appears on the screen. The becomeFirstResponder method is called on the UITextView, which sets focus on it and opens the keyboard for user input.
In summary, a UITextView becomes a first responder when the user taps on it or when the app programmatically calls the becomeFirstResponder method on it. This allows the app to automatically set focus on a text field and open the keyboard for user input.
UITextView在用户点击文本框时会自动成为第一响应者（First Responder）。只要为UITextView启用了用户交互功能，当用户点击文本框时，键盘就会出现。
我们可以通过监听委托方法textViewDidBeginEditing或者更广泛地监听键盘出现的通知（UIKeyboardWillShowNotification和UIKeyboardDidShowNotification）来监测键盘的出现。
此外，还有一些方法可以在不调用resignFirstResponder方法的情况下关闭键盘，比如在容器视图上调用endEditing:方法或者设置滚动视图的UIScrollViewKeyboardDismissMode属性。
需要注意的是，在模拟器上，即使一切正常工作，键盘仍然可能不会出现。这种情况下，你只需要确保在模拟器上切换键盘硬件（CMD+K）即可。
UITextView在用户点击文本框时会自动成为第一响应者，可以通过委托方法或监听键盘出现的通知来监测键盘的出现，还可以使用其他方法关闭键盘。在模拟器上，如果键盘没有出现，需要检查是否切换了键盘硬件。