iphone-时间(应用程序隐藏)和时间(应用程序出现)之间的差异
如何从appEnterBackground中获取日期并从appEnterForeground中删除,然后在标签中显示差异。 这是到目前为止我的代码iphone-时间(应用程序隐藏)和时间(应用程序出现)之间的差异,iphone,objective-c,nsstring,xcode4,Iphone,Objective C,Nsstring,Xcode4,如何从appEnterBackground中获取日期并从appEnterForeground中删除,然后在标签中显示差异。 这是到目前为止我的代码 **.h** NSTimeInterval appEnteredBackground; NSTimeInterval appEnteredForeground; NSTimeInterval difference; **.m** - (void)applicationDidEnterBackground:(UIAppl
**.h**
NSTimeInterval appEnteredBackground;
NSTimeInterval appEnteredForeground;
NSTimeInterval difference;
**.m**
- (void)applicationDidEnterBackground:(UIApplication *)application
{
appEnteredBackground = [NSDate timeIntervalSinceReferenceDate];
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
appEnteredForeground = [NSDate timeIntervalSinceReferenceDate];
difference = appEnteredForeground - appEnteredBackground;
NSLog(@"Duration is %@",[NSDate dateWithTimeIntervalSinceReferenceDate: difference]);
NSLog(@"Duration is %@", [NSString stringWithFormat:@"%f", difference]);
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
NSString *time = [NSString stringWithFormat:@"%f", difference]; **//ERROR HERE (variable not used)**
[dateFormatter release];
}
任何帮助都会非常好我认为您在这里没有错误。如果正确计算了时差,则可以构建一个带有“说明”的字符串,但不使用它 若要查看所有功能是否正常,请在方法结束前尝试以下操作:
NSLog(@"Computed time was: %@", time);
你应该关心时间变量,因为你没有积极地使用它。要测量这种类型的事件(或事件的差异),你需要分辨率小于一秒的东西。有一个“c”接口来获取机器时间,这是处理器内部无硬件运行的“滴答声” 使用这个秒表类,您可以获得非常好的计时(毫秒、微秒,如果您相信的话) 秒表.h
#import <Foundation/Foundation.h>
@interface StopWatch : NSObject
{
uint64_t _start;
uint64_t _stop;
uint64_t _elapsed;
}
-(void) Start;
-(void) Stop;
-(void) StopWithContext:(NSString*) context;
-(double) seconds;
-(NSString*) description;
+(StopWatch*) stopWatch;
-(StopWatch*) init;
@end
@onnoweb://ERROR HERE(变量未使用)我想将“difference”的值输入到标签或字符串中,以便我可以在计算中使用它……可能重复您已经问过的这个问题。再问一次也帮不了你。@乔纳森:只是迷路了,需要一些帮助。你应该阅读
NSDate
的文档。看起来你在胡乱尝试。文档告诉您像+datewithtimeintervalcescereferencedate:
这样的方法可以做什么。
#import "StopWatch.h"
#include <mach/mach_time.h>
@implementation StopWatch
-(void) Start
{
_stop = 0;
_elapsed = 0;
_start = mach_absolute_time();
}
-(void) Stop
{
_stop = mach_absolute_time();
if(_stop > _start)
{
_elapsed = _stop - _start;
}
else
{
_elapsed = 0;
}
_start = mach_absolute_time();
}
-(void) StopWithContext:(NSString*) context
{
_stop = mach_absolute_time();
if(_stop > _start)
{
_elapsed = _stop - _start;
}
else
{
_elapsed = 0;
}
NSLog([NSString stringWithFormat:@"[%@] Stopped at %f",context,[self seconds]]);
_start = mach_absolute_time();
}
-(double) seconds
{
if(_elapsed > 0)
{
uint64_t elapsedTimeNano = 0;
mach_timebase_info_data_t timeBaseInfo;
mach_timebase_info(&timeBaseInfo);
elapsedTimeNano = _elapsed * timeBaseInfo.numer / timeBaseInfo.denom;
double elapsedSeconds = elapsedTimeNano * 1.0E-9;
return elapsedSeconds;
}
return 0.0;
}
-(NSString*) description
{
return [NSString stringWithFormat:@"%f secs.",[self seconds]];
}
+(StopWatch*) stopWatch
{
StopWatch* obj = [[[StopWatch alloc] init] autorelease];
return obj;
}
-(StopWatch*) init
{
[super init];
return self;
}
@end
-(void)SomeFunc
{
StopWatch* stopWatch = [StopWatch stopWatch];
[stopWatch Start];
... do stuff
[stopWatch StopWithContext:[NSString stringWithFormat:@"Created %d Records",[records count]]];
}