iPhone 上的键盘和起床状态

Question

如何判断键盘是否已打开？

我有一个 UISearchbar 实例，它成为第一响应者。

当键盘出现时，通知会作为 API 的一部分发送出去，但我不想立即对此做出回应。我可以用布尔状态记录它，但这看起来很笨拙。我想知道是否有“吸气剂”，我可以打电话询问。

Answer 1

我就是这样做的：

KeyboardStateListener.h

@interface KeyboardStateListener : NSObject {
    BOOL _isVisible;
}
+ (KeyboardStateListener *) sharedInstance;
@property (nonatomic, readonly, getter=isVisible) BOOL visible;
@end

KeyboardStateListener.m

#import "KeyboardStateListener.h"

static KeyboardStateListener *sharedObj;

@implementation KeyboardStateListener

+ (KeyboardStateListener *)sharedInstance
{
    return sharedObj;
}
+ (void)load
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    sharedObj = [[self alloc] init];
    [pool release];
}
- (BOOL)isVisible
{
    return _isVisible;
}
- (void)didShow
{
    _isVisible = YES;
}
- (void)didHide
{
    _isVisible = NO;
}
- (id)init
{
    if ((self = [super init])) {
        NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
        [center addObserver:self selector:@selector(didShow) name:UIKeyboardDidShowNotification object:nil];
        [center addObserver:self selector:@selector(didHide) name:UIKeyboardWillHideNotification object:nil];
    }
    return self;
}

-(void) dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    [super dealloc];
}

@end

然后用它来计算其余的：

KeyboardStateListener *obj = [KeyboardStateListener sharedInstance];
if ([obj isVisible]) {
    //Keyboard is up
}

Answer 2

我能想到的唯一可靠的方法就是按照你说的去做。使用这样的通知：

[[NSNotificationCenter defaultCenter] addObserver:self 
                                         selector:@selector(keyboardWillShow:) 
                                             name:UIKeyboardWillShowNotification 
                                           object:nil];

然后

[[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(keyboardWillHide:) 
                                                 name:UIKeyboardWillHideNotification 
                                               object:nil];

除此之外，您也许可以迭代视图子视图并查找键盘，例如：

UIView *keyboard = nil;

for (UIView *potentialKeyboard in [myWindow subviews]) {

    // iOS 4
    if ([[potentialKeyboard description] hasPrefix:@"<UIPeripheralHostView"]) {
      potentialKeyboard = [[potentialKeyboard subviews] objectAtIndex:0];
    }                                                                                

    if ([[potentialKeyboard description] hasPrefix:@"<UIKeyboard"]) {
      keyboard = potentialKeyboard;
      break;
    }
  }

但我不确定当 SDK 更改时这是否会中断...

也许使用此方法并添加窗口的一个类别，以便您始终可以向窗口询问键盘......只是一个想法。