define WeakObj(o) __weak typeof(o) weak##o = o;
@interface ViewController()@property(weak, nonatomic) IBOutlet NSLayoutConstraint * bottomCons;//textV距离屏幕底部的约束，默认设置为0
@end
-
(void) viewDidLoad { [super viewDidLoad];
// 监听键盘 将要 弹出和隐藏
[[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(keyboardWillShowOrHide: ) name: UIKeyboardWillShowNotification object: nil];[[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(keyboardWillShowOrHide: ) name: UIKeyboardWillHideNotification object: nil];
}
/** 第三方键盘将要显示时， 此方法会被调用 3次，键盘y坐标依次为0，226，292:
2016-08-04 14:50:40.810 YZInputViewDemo[883:260581] 0.000000
2016-08-04 14:50:40.976 YZInputViewDemo[883:260581] 226.000000
2016-08-04 14:50:41.001 YZInputViewDemo[883:260581] 292.000000
即将隐藏时，拿到的键盘高度是292，所以代码中直接写死为 0
*/
-
(void) keyboardWillShowOrHide: (NSNotification * ) note {
//注意，字典里存放的都是对象，要把对象转为CGRect结构体，使用CGRectValue方法。
CGRect keyboardFrame = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
CGFloat duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] floatValue];WeakObj(self);
NSLog(@"%f", keyboardFrame.size.height);warning: 修改底部视图距离底部的间距,
之前下面方法放在keyboardWillChangeFrame：方法中，导致第3次292时，_bottomCons.constant == 0不成立，于是_bottomCons.constant被重新赋值为0！这就是bug原因。解决办法就是监听将要显示和将要消失两个通知！
// _bottomCons.constant = (_bottomCons.constant == 0 ? endFrame.size.height :
// 0);
// 修改底部视图距离底部的间距
if ([note.name isEqualToString: @"UIKeyboardWillHideNotification"]) {
_bottomCons.constant = 0;
} else { // willShow
_bottomCons.constant = keyboardFrame.size.height;
}[UIView animateWithDuration: duration animations: ^{ [weakself.view layoutIfNeeded];
}];
}
@end
