One, midnight Countdown "Getting Started with Apple iOS instance programming tutorial"

The app is used to calculate the remaining time from 12:00 midnight.

Current version of SDK 8.4 Xcode

Run Xcode Select Create a new Xcode project->single View application named minutestomidnight

(1) Open ViewController.h file in Xcode

(Red is the added code)

#import <UIKit/UIKit.h>

@interface viewcontroller: uiviewcontroller

{

nstimer *timer;

iboutlet UILabel *countdownlabel;

}

@property (nonatomic,retain)nstimer *timer;

@property (nonatomic,retain)iboutlet UILabel *countdownlabel;

-(void) OnTimer;

@end

(2) Open viewcontroller.m file in Xcode

#import "ViewController.h"

@interface viewcontroller ()

@end

@implementation Viewcontroller

@synthesize timer;

@synthesize Countdownlabel;

-(void) viewdidload {

[Super viewdidload];

additional setup after loading the view, typically from a nib.

[countdownlabel setFont: [uifont fontwithname:@ "Dblcdtempblack" Size :]];//font size

    Countdownlabel text = @ "00:00:00" ; Initialize the value of the label

self. Timer = [nstimer scheduledtimerwithtimeinterval:1.0 target: Self selector:@selector(onTimer) userInfo:nil repeats:YES ];

/*

Scheduledtimerwithtimeinterval: (nstimeinterval) seconds

Book a timer and set a time interval. Represents a value that enters a time interval object, in seconds, of a >0 floating-point type, and if the value is <0, the system defaults to 0.1

Target: (ID) atarget

Represents the Sent object, such as self

Selector: (SEL) Aselector

Method selector, which, within the time interval, chooses to invoke an instance method

UserInfo: (ID) userInfo

This parameter can be nil, and the timer is retained and freed by the object you specify when the timer fails.

Repeats: (BOOL) Yesorno

When yes, the timer loops continuously until it expires or is released, and when no, the timer is sent out once and then fails.

*/

}

-(void) didreceivememorywarning {

[Super didreceivememorywarning];

//Dispose of any resources, can be recreated.

}

-(void) OnTimer

{

nsdate *now = [nsdate date];

Nscalendar *gregorian = [[nscalendar alloc]initwithcalendaridentifier: Nscalendaridentifiergregorian];

   /* nsdate--Represents an absolute point in time
       nstimezone--time zone information
  & nbsp    nslocale--Localization information
       nsdatecomponents--a class that encapsulates a specific date, time, week, quarter, and so on
       nscalendar--Calendar class, which provides most of the date compute interfaces and allows you to convert between NSDate and nsdatecomponents
        NSDateFormatter--Used to convert between dates and strings

Nscalendar Calendar class ****//

The following methods are available for creating or initializing

+ (ID) Currentcalendar;

Get the current user's logical calendar (logical calendars)

+ (ID) Autoupdatingcurrentcalendar;

Get the current user's logical calendar (logical calendar), ...

-(ID) Initwithcalendaridentifier: (NSString *) identifier;

Initialize to various calendars. The range of identifier can be:

Nscalendaridentifiergregorian Solar Calendar

nscalendaridentifierbuddhist Buddhist Calendar

Nscalendaridentifierchinese China calendar

nscalendaridentifierhebrew Hebrew calendar

nscalendaridentifierislamic Islamic Calendar

nscalendaridentifierislamiccivil Islamic Civil calendar

Nscalendaridentifierjapanese Japan Calendar

*/

nsdatecomponents *datecomponents = [Gregorian components:(kcfcalendarunithour| Kcfcalendarunitminute| Kcfcalendarunitsecond) fromdate: now];

Nsinteger hour = [datecomponents hour];

nsinteger min = [datecomponents minute];

Nsinteger sec = [datecomponents second];

SEC = -sec;

min = -min;

hour = hour;

Countdownlabel. Text = [nsstring stringwithformat:@ "%ld:%ld:%ld", hour,min,sec];

}

@end

(3) UIView interface settings
-Black background

Click Main.storyboard

Select View Controller->view

Set the background to black

Select Attributes Inspector->background->black Color

(4) Add UILabel display countdown time

-Red Font

Select: Tools--Library; Drag a Label from the Library display menu to Main View

Color and font size of fonts from label Attributes

(5) write to the UILabel class file

Right-click the Label control and move the mouse over the circle behind "New referencing Outlet"; The circle becomes (+); Drag to a straight line to connect to the "view Controller";
Release the mouse Select button appears "Countdownlabel"; Pick it up.

Select: File--Save

Finally, in XCode, choose Build and then Running

(6) Simulator

This article originates from the online a blog tutorial, after I revise and test. Original Blog Address http://blog.sina.com.cn/s/blog_5fae23350100djg2.html

One, midnight Countdown "Getting Started with Apple iOS instance programming tutorial"