iOS边练边学--通知机制和键盘处理小练习

一、发送通知

 NSNotification *note = [NSNotification notificationWithName:@"通知的名称，随便写，例如：你妈叫你回家吃饭" object:self userInfo:@{@"time":@"11:30",
         @"desc":@"回家吃饭"
                         }];
     NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
     [center postNotification:note];

二、接收通知：

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardChange:) name:UIKeyboardWillChangeFrameNotification object:nil];

三、键盘处理小练习

　　注意事项：tableView的高度约束取消，如果约束在的话，tableView无法实现上移，只能实现往上压缩

　　正确做法：设置tableView的高度约束等于父类约束的高度减去最下面工具栏的高度，如图：

　　<1>将键盘的显示和隐藏分开处理的情况

　　接收通知的代码：

 - (void)viewDidLoad {
     [super viewDidLoad];
     // addObserver-谁来接收 @Selector-接收完成需要执行的方法，带一个参数，接收通知中心发来的NSNotofication对象
     // object-发送消息的对象，nil-不管谁发送的，只要是name中的消息都接收，这里监听的是键盘的即将弹出的消息，系统发出的消息是字符串常亮
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
     // 接收键盘隐藏的通知
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
 }

　　接收到通知后的处理代码：

 - (void)keyboardWillShow:(NSNotification *)note
 {
     // 取出时间
     CGFloat duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
     // 取出键盘显示出来后的最终frame
     CGRect rect = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
     // 改变约束
     self.bottomSpacing.constant = rect.size.height;
     // 动画效果
     [UIView animateWithDuration:duration animations:^{
         [self.view layoutIfNeeded];
     }];
 }

 - (void)keyboardWillHide:(NSNotification *)note
 {
     // 取出时间
     CGFloat duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
     // 约束改为0
     self.bottomSpacing.constant = ;
     [UIView animateWithDuration:duration animations:^{
         [self.view layoutIfNeeded];
     }];
 }

　　<2>将键盘显示和隐藏一起处理的情况

- (void)viewDidLoad {
    [super viewDidLoad];
    // 接收通知
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardChange:) name:UIKeyboardWillChangeFrameNotification object:nil];
}

 - (void)keyboardChange:(NSNotification *)note
 {
     // 取出时间
     CGFloat duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
     // 取出键盘最终的frame
     CGRect rect = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
     self.bottomSpacing.constant = [UIScreen mainScreen].bounds.size.height - rect.origin.y;
     [UIView animateWithDuration:duration animations:^{
         [self.view layoutIfNeeded];
     }];
 }

 - (void)keyboardChange:(NSNotification *)note
 {
     // 取出时间
     CGFloat duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
     // 取出键盘最终的frame
     CGRect rect = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
     self.bottomSpacing.constant = [UIScreen mainScreen].bounds.size.height - rect.origin.y;
     [UIView animateWithDuration:duration animations:^{
         [self.view layoutIfNeeded];
     }];
 }

四、最后一步，也是最重要的一步，记得取消注册的通知监听器

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