高精度的Timer（Objetive C）

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发布时间：2019-06-22

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－、NSTimer定时精度

　　在实现一个坚实系统剪贴板变化当程序中，发现使用NSTimer精度达不到要求，类似当问题可以在stackoverflow中找到，如下：

经过查询文档之后，timer当触发是在runloop当循环中检查是否已经到达触发条件，如果没有到达，就在下一次循环中继续检查。因此NSTimer当精度受制与Runloop的循环时间，并且收到线程调度的影响，文档中说明是50～100ms，对于一般的应用可以满足。

二、更精确的Timer

　　在stackoverflow上面搜索如何获得更精确的timer之后，发现下面这种方式能解决一般问题，但是精度还是大于200ms，但是比NSTimer更稳定一些，当程序退到后台之后，仍旧能正常触发。

　　解决办法：

／／建立新线程[NSThread detachNewThreadSelector:@selector(timer) toTarget:self withObject:nil]; //make a new thread／／在线程中使用NSdate进行判断- (void)timer {        @autoreleasepool {        NSDate *startDate = [NSDate date];        while (YES) {            usleep(10000);            if([[NSDate date] timeIntervalSinceDate:startDate] >= watch_interval)            {                startDate = [NSDate date];                objc_msgSend(self,@selector(watchLoop),nil);            }        }            }}

　　这个方法仍然有弊端，可能是NSDate到更新间隔，导致200ms到间隔不能缩小。

三、更精确到定时器，如果想获得更精确到定时器，可以参考apple到这份文档，文档中不建议使用该定时器，除非特别需要。

High Precision Timers in iOS / OS X

链接：

四、监视定时器变化到代码

.h 文件

////  PastboardWatcher.h//  PastboardWatcher////  Created by  on 14-3-20.//  Copyright (c) 2014年 master. All rights reserved.//#import 
     
      @protocol PastboardWatcherDelegate;@interface PastboardWatcher : NSObject+ (id)shanreInstance;- (void)registerObsever:(id
      
       )delegate;- (void)removeDelegate:(id
       
        )delegate;@end@protocol PastboardWatcherDelegate 
        
         - (void)generalPastboardDidChange;@end

.m文件

////  PastboardWatcher.m//  PastboardWatcher////  Created by  on 14-3-20.//  Copyright (c) 2014年 master. All rights reserved.//#import 
     
      #import "PastboardWatcher.h"static const NSTimeInterval watch_interval = 0.2;@interface PastboardWatcher ()@property (nonatomic, strong) NSMutableArray *obseverArray;@property (nonatomic, assign) NSInteger      changeCount;@property (nonatomic, strong) NSRecursiveLock *lock;@end@implementation PastboardWatcher+ (id)shanreInstance{    static PastboardWatcher *instance = nil;    static dispatch_once_t once_token;    dispatch_once(&once_token,^{        instance = [[PastboardWatcher alloc] init];                  });    return instance;}- (id)init{    if(self = [super init])    {        _obseverArray = [[NSMutableArray alloc] init];        _changeCount  = [[NSPasteboard generalPasteboard] changeCount];        _lock         = [[NSRecursiveLock alloc] init];        [NSThread detachNewThreadSelector:@selector(timer) toTarget:self withObject:nil]; //make a new thread    }    return self;}- (void)registerObsever:(id
      
       )delegate{    [_lock lock];    [_obseverArray addObject:delegate];    [_lock unlock];}- (void)removeDelegate:(id
       
        )delegate{    [_lock lock];    NSInteger findIndex = [_obseverArray indexOfObject:delegate];    if(findIndex != NSNotFound) [_obseverArray removeObjectAtIndex:findIndex];    [_lock unlock];}- (void)timer {        @autoreleasepool {        NSDate *startDate = [NSDate date];        while (YES) {            usleep(10000);            if([[NSDate date] timeIntervalSinceDate:startDate] >= watch_interval)            {                startDate = [NSDate date];                objc_msgSend(self,@selector(watchLoop),nil);            }        }            }}- (void)watchLoop{    NSInteger current_changeCount = [NSPasteboard generalPasteboard].changeCount;    if(current_changeCount != _changeCount)    {        _changeCount = current_changeCount;        objc_msgSend(self, @selector(notifyObseverChange),nil);    }}- (void)notifyObseverChange{    [_lock lock];    NSArray *tempArray = [_obseverArray copy];    [_lock unlock];        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{                for (id
        
          delegate in tempArray) {            if([delegate respondsToSelector:@selector(generalPastboardDidChange)])            {                objc_msgSend(delegate, @selector(generalPastboardDidChange));            }        }            });}@end

转载于:https://www.cnblogs.com/mystackflow/p/3614741.html

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