动态隐藏NavigationBar

//1.当我们的手离开屏幕时候隐藏
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{ 
if(velocity.y > 0) 
{
[self.navigationController setNavigationBarHidden:YES animated:YES];
} else {
[self.navigationController setNavigationBarHidden:NO animated:YES]; 
}
}
velocity.y这个量，在上滑和下滑时，变化极小（小数），但是因为方向不同，有正负之分，这就很好处理了。
//2.在滑动过程中隐藏
//像safari
(1) 
self.navigationController.hidesBarsOnSwipe = YES;
(2)
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
 CGFloat offsetY = scrollView.contentOffset.y + __tableView.contentInset.top;
 CGFloat panTranslationY = [scrollView.panGestureRecognizer translationInView:self.tableView].y;
 if (offsetY > 64) {
 if (panTranslationY > 0) 
{ 
//下滑趋势，显示 
[self.navigationController setNavigationBarHidden:NO animated:YES];
} else { 
//上滑趋势，隐藏 
[self.navigationController setNavigationBarHidden:YES animated:YES]; 
}
} else {
[self.navigationController setNavigationBarHidden:NO animated:YES]; 
}
}
这里的offsetY > 64只是为了在视图滑过navigationBar的高度之后才开始处理，防止影响展示效果。panTranslationY是scrollView的pan手势的手指位置的y值，可能不是太好，因为panTranslationY这个值在较小幅度上下滑动时，可能都为正或都为负，这就使得这一方式不太灵敏.

设置倒计时

//第一种方法
//点击button倒计时
#import "ViewController.h"
@interface ViewController ()
@property (nonatomic, strong) UIButton * timeButton;
@property (nonatomic, strong) NSTimer * timer;
@property (nonatomic, strong)UIButton * btn;
@end@implementation ViewController
{ 
NSInteger _time;
}
- (void)viewDidLoad {
[super viewDidLoad]; 
_time = 5; 
self.btn = [UIButton buttonWithType:UIButtonTypeCustom]; _btn.backgroundColor = [UIColor orangeColor];
[_btn setTitle:@"获取验证码" forState:UIControlStateNormal]; _btn.titleLabel.font = [UIFont systemFontOfSize:15];
[_timeButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[_btn addTarget:self action:@selector(btnAction:) forControlEvents:UIControlEventTouchUpInside];
[self refreshButtonWidth]; 
[self.view addSubview:self.btn];
}
- (void)refreshButtonWidth{ 
CGFloat width = 0; 
if (_btn.enabled){
 width = 100; 
} else { 
width = 200;
} 
_btn.center = CGPointMake(self.view.frame.size.width/2, 200);
_btn.bounds = CGRectMake(0, 0, width, 40); 
//每次刷新，保证区域正确
[_btn setBackgroundImage:[self imageWithColor:[UIColor orangeColor] andSize:_btn.frame.size] forState:UIControlStateNormal];
[_btn setBackgroundImage:[self imageWithColor:[UIColor lightGrayColor] andSize:_btn.frame.size] forState:UIControlStateDisabled];
}
- (UIImage *)imageWithColor:(UIColor *)color andSize:(CGSize)aSize{
 CGRect rect = CGRectMake(0.0f, 0.0f, aSize.width, aSize.height); UIGraphicsBeginImageContext(rect.size);
 CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetFillColorWithColor(context, [color CGColor]); CGContextFillRect(context, rect);
 UIImage *image = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext();
return image;
}
- (void)btnAction:(UIButton *)sender{
sender.enabled = NO;
[self refreshButtonWidth];
[sender setTitle:[NSString stringWithFormat:@"获取验证码(%zi)", _time] forState:UIControlStateNormal]; 
_timer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(timeDown) userInfo:nil repeats:YES];
}
- (void)timeDown{ 
_time --;
 if (_time == 0) {
 [_btn setTitle:@"重新获取" forState:UIControlStateNormal]; _btn.enabled = YES; 
[self refreshButtonWidth]; 
[_timer invalidate]; 
_timer = nil; 
_time = 5 ; 
return; 
} 
[_btn setTitle:[NSString stringWithFormat:@"获取验证码(%zi)", _time] forState:UIControlStateNormal];
}

###################################################
//第二种方法
#pragma mark -点击发送验证码
- (void)sendMessage:(UIButton *)btn{
if (self.phoneField.text.length == 0) { 
[self remindMessage:@"请输入正确的手机号"];
}else{ 
__block int timeout=60; 
//倒计时时间 
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue); dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0);
 //每秒执行 
dispatch_source_set_event_handler(_timer, ^{ 
if(timeout<=0){ 
//倒计时结束，关闭 
dispatch_source_cancel(_timer); dispatch_async(dispatch_get_main_queue(), ^{ 
// 设置界面的按钮显示 根据自己需求设置 
[btn setTitle:@"发送验证码" forState:UIControlStateNormal]; btn.userInteractionEnabled = YES; 
}); 
}else{ 
int seconds = timeout % 60;
NSString *strTime = [NSString stringWithFormat:@"%d", seconds];
if ([strTime isEqualToString:@"0"]) {
 strTime = [NSString stringWithFormat:@"%d",60];
 } 
dispatch_async(dispatch_get_main_queue(), ^{ 
//设置界面的按钮显示 根据自己需求设置 
//NSLog(@"____%@",strTime);
[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:1]; 
[btn setTitle:[NSString stringWithFormat:@"%@秒后重新发送",strTime] forState:UIControlStateNormal];
[UIView commitAnimations]; 
btn.userInteractionEnabled = NO;
 });
 timeout--;
 } 
}); 
dispatch_resume(_timer);
}

修改textFieldplaceholder字体颜色和大小

textField.placeholder = @"username is in here!"; [/p][textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];  
[textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];

去掉导航栏下边的黑线

[self.navigationController.navigationBar setBackgroundImage:[[UIImage alloc] init] forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.shadowImage = [[UIImage alloc] init];

NSDate与NSString的相互转化

-(NSString *)dateToString:(NSDate *)date {
  // 初始化时间格式控制器
  NSDateFormatter *matter = [[NSDateFormatter alloc] init];
  // 设置设计格式
  [matter setDateFormat:@"yyyy-MM-dd hh:mm:ss zzz"];
  // 进行转换
  NSString *dateStr = [matter stringFromDate:date];
  return dateStr;
}
-(NSDate *)stringToDate:(NSString *)dateStr {
 
  // 初始化时间格式控制器
  NSDateFormatter *matter = [[NSDateFormatter alloc] init];
  // 设置设计格式
  [matter setDateFormat:@"yyyy-MM-dd hh:mm:ss zzz"];
  // 进行转换
  NSDate *date = [matter dateFromString:dateStr];
  return date;
}