07tableView键盘消失_滚动到最后一行_文字占据的矩形块_图片拉伸_圆角剪裁_单元格选中样式_移除监听者

一、气泡聊天
1.滚动到最后一行

 [_tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];

2.获取文字占据的矩形空间
Size:限制矩形块的宽/高
options:NSStringDrawingUsesLineFragmentOrigin 每一行文字所占据的矩形空间
attributes:设置文字的属性
context:上下文（一般为nil）

 CGRect messageRect = [message boundingRectWithSize:CGSizeMake(200, LONG_MAX) options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:17]} context:nil];

3.图片拉伸
(LeftCapWidth,topCapHeight) 该点一般位于图片中心点附近

 UIImage *newImg = [oldImg stretchableImageWithLeftCapWidth:22 topCapHeight:16];

4.设置聊天头像（图片剪裁）

 selfCell.selfHeader.image = [UIImage imageNamed:@"0.jpg"];
 selfCell.selfHeader.layer.cornerRadius = 20;
 selfCell.selfHeader.clipsToBounds = YES;

5.单元格选中样式

 selfCell.selectionStyle = UITableViewCellSelectionStyleNone;

6.给tableView加上手势，触发键盘消失

    UITapGestureRecognizer *gestureRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(hideKeyboard)];
    [_tableView addGestureRecognizer:gestureRecognizer];
- (void)hideKeyboard
{
    [_messageTf resignFirstResponder];
}

二、移除监听者
文件：ViewController.m

- (void)dealloc
{
    //如果在自定义内部，将该类的对象注册为监听者
    //若对象被释放，必须把监听者从通知中心移除
    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"吃饭" object:nil];
    [super dealloc];
}
- (void)viewDidLoad {
    [super viewDidLoad];
    //1.如果将某个VC（viewController）注册为Observer，当VC被释放的时候，系统会自动把Observer（VC）从通知中心移除掉
//    NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
//    [center addObserver:self selector:@selector(changeAction) name:@"xxx" object:nil];
    People *people = [[People alloc]init];
    [people release];
}

文件：People.m

- (id)init
{
    self = [super init];
    if (self)
    {
        //在自定义类内部注册了一个监听者，
        NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
        [center addObserver:self selector:@selector(eat) name:@"吃饭" object:nil];
    }
    return self;
}

自定义ViewController NavigationController