iphone-时间（隐藏应用）和时间（出现应用）之间的时差。
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如何从appEnterBackground获取日期并从appEnterForeground获取日期，然后在标签中显示差异。
到目前为止，这是我的代码。
**.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];
}
没有找到相关结果
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2 个回复
镶骄册筷
您应该关心那个变量，因为您没有积极使用它。济畦刨
#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#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方法，该方法返回一个自动释放的对象。 调用后，请使用方法获取经过的时间。再次呼叫重新启动。或按ѭ9停止。致电之后，您仍然可以随时读取时间（致电call7ѭ）。 函数中的示例（执行的计时调用）-(void)SomeFunc { StopWatch* stopWatch = [StopWatch stopWatch]; [stopWatch Start]; ... do stuff [stopWatch StopWithContext:[NSString stringWithFormat:@\"Created %d Records\",[records count]]]; }