31、遍历histogramview里面的所有对象：
UILabel *label in [histogramview subviews];

32、判断对象是否属于某个类：
[label isKindOfClass:[UILabel class]];

32、UIColor自定义颜色：
viewController.view.backgroundColor = [UIColor colorWithRed:192.0f/255.0f green:204.0f/255.0f blue:255.0f/255.0f alpha:0.5f];

33 、自动调用数字键盘：
[self.passwordinput setKeyboardType:UIKeyboardTypeNumbersAndPunctuation];

34、获取iPhone序列号：
UIDevice *mydevice = [UIDevice currentDevice];
NSString *deviceID = [mydevice uniqueIdentifier];
获取IPhone/IPad设备信息
NSLog([[UIDevice currentDevice] name]);
// Name of the phone as named by user
NSLog([[UIDevice currentDevice] uniqueIdentifier]);
// A GUID like string
NSLog([[UIDevice currentDevice] systemName]);
// "iPhone OS"
NSLog([[UIDevice currentDevice] systemVersion]);
// "2.2.1"
NSLog([[UIDevice currentDevice] model]);
// "iPhone" on both devices
NSLog([[UIDevice currentDevice] localizedModel]);
// "iPhone" on both devices

35、不让iphone进入休眠模式：
[UIApplication sharedApplication].idleTimerDisabled=YES;

36、一定时间后触发事件：
[self performSelector:@selector(getIT) withObject:self afterDelay:2.0f];//2秒后执行getIT函数

37、更改navication bar背景
在m文件顶端加入如下代码：
@interface UINavigationBar (MyCustomNavBar)
@end
@implementation UINavigationBar (MyCustomNavBar)
- (void) drawRect:(CGRect)rect {
    UIImage *barImage = [UIImage imageNamed:@"bar.png"];
    [barImage drawInRect:rect];
}
@end

38、更改tab bar背景
在m文件顶端加入如下代码：
@implementation UITabBar (CustomImage)
- (void)drawRect:(CGRect)rect {
    UIImage *image = [UIImage imageNamed: @"bar.png"];
    [image drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];
}
@end

39、切换tab bar时触发的事件
- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController {
    NSLog(@"%i",viewController.tabBarItem.tag);
}

40、更改UISearch Bar的按钮文字
for(id cc in [searchtext subviews]){
    if([cc isKindOfClass:[UIButton class]]){
        [btn setTitle:@"Search"  forState:UIControlStateNormal];
    }
}