ios - becomeFirstResponder 在 iOS 8 中不起作用

Question

我正在使用 UITextField 的方法 becomeFirstResponder 来显示键盘。这在 iOS 7 中有效。但在 iOS 8 中，此方法不显示键盘。

 UITextField *txtAddNew = [[UITextField alloc] initWithFrame:CGRectMake(10,10,240, 21)];
 txtAddNew.font = [UIFont fontWithName:@"Helvetica" size:16];
 txtAddNew.clearButtonMode = UITextFieldViewModeWhileEditing;
 txtAddNew.returnKeyType = UIReturnKeyDone;
 txtAddNew.delegate = self;
 txtAddNew.autocorrectionType = UITextAutocorrectionTypeNo;
 txtAddNew.tag = 15;

 // Open keyboard
 [txtAddNew becomeFirstResponder];

有什么办法可以在 iOS 8 中实现吗？

Answer 1

尝试像下面这样调用becomeFirstResponder

[txtAddNew performSelector:@selector(becomeFirstResponder) withObject:nil afterDelay:0];

根据苹果公司的说法，

A responder object only becomes the first responder if the current responder can resign first-responder status (canResignFirstResponder) and the new responder can become first responder.

You may call this method to make a responder object such as a view the first responder. 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.