每次我的应用程序从挂起模式唤醒时,我正在记录(写入文件)
backgroundTimeRemaining值,就在我开始使用到期处理程序的UIApplication后台任务之前,就像这样(在我的方法中发出网络请求)：
if([[UIApplication sharedApplication] applicationState] == UIApplicationStateBackground){
[Logger logIntoFileNamed:@"log" withContent:[NSString stringWithFormat:@" state %ld,background time remaining %.2f",(long)[[UIApplication sharedApplication] applicationState],[[UIApplication sharedApplication] backgroundTimeRemaining ]] andPrettyTime:true];
UIApplication* app = [UIApplication sharedApplication];
__block UIBackgroundTaskIdentifier task = [app beginBackgroundTaskWithExpirationHandler:^{
[app endBackgroundTask:task];
task = UIBackgroundTaskInvalid;
[Logger logIntoFileNamed:@"log" withContent:@" expiration handler executed " andPrettyTime:true];
}];
}
根据文档,如果app在前台,backgroundTimeRemaining的值可能很大：
While the app is running in the foreground,the value in this property
remains suitably large.
但这不是一个例子.我的方法被执行,因为应用程序状态等于UIApplicationStateBackground.
我在这里错过了什么？
解决方法
是的,根据文件：
A value of backgroundTimeRemaining can be big if app is in the
foreground.
在提供正确的backgroundTimeRemaining之前,applicationDidEnterBackground需要在状态之间进行一些时间.这应该在~180左右开始.使用dispatch_async在异步线程中运行它并过滤掉Foreground值(> 180).
- (void)applicationDidEnterBackground:(UIApplication *)application
{
if([[UIDevice currentDevice] respondsToSelector:@selector(isMultitaskingSupported)])
{
NSLog(@"Multitasking Supported");
__block UIBackgroundTaskIdentifier background_task;
background_task = [application beginBackgroundTaskWithExpirationHandler:^ {
//Clean up code. Tell the system that we are done.
[application endBackgroundTask: background_task];
background_task = UIBackgroundTaskInvalid;
}];
//To make the code block asynchronous
dispatch_async(dispatch_get_main_queue(),^{
//### background task starts
NSLog(@"Running in the background\n");
while(TRUE)
{
//#### Filter Foreground Values
if ([[UIApplication sharedApplication] backgroundTimeRemaining] < 180) {
NSLog(@"Background time Remaining: %f",[[UIApplication sharedApplication] backgroundTimeRemaining]);
[NSThread sleepForTimeInterval:1]; //wait for 1 sec
}
}
//#### background task ends
//Clean up code. Tell the system that we are done.
[application endBackgroundTask: background_task];
background_task = UIBackgroundTaskInvalid;
});
}
else
{
NSLog(@"Multitasking Not Supported");
}
}
