iOS 多任务处理不工作

Question

- (IBAction)buttonPressed:(id)sender
{
UIDevice *device = [UIDevice currentDevice];
device.batteryMonitoringEnabled = YES;
if ([[UIDevice currentDevice] isMultitaskingSupported]) {
    [self beingBackgroundUpdateTask];
}
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(batteryChanged:) name:@"UIDeviceBatteryLevelDidChangeNotification" object:device];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(batteryChanged:) name:@"UIDeviceBatteryStateDidChangeNotification" object:device];
[self currentBatteryState];


}


- (void) beingBackgroundUpdateTask
{
    self->backgroundUpdateTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        [self endBackgroundUpdateTask];
    }];
}


- (void) endBackgroundUpdateTask
{
    [[UIApplication sharedApplication] endBackgroundTask: self->backgroundUpdateTask];
    self->backgroundUpdateTask = UIBackgroundTaskInvalid;
}

由于某种原因，通知没有被遵守。难道我做错了什么？我想在不插电的情况下观察长达 10 分钟

Answer 1

您不应该在 buttonPressed: 方法中调用 endBackgroundUpdateTask，因为那样会取消您的后台任务。尝试删除此代码:

if ([[UIDevice currentDevice] isMultitaskingSupported]) {
    [self endBackgroundUpdateTask];
}

此外，您应该将 UIDeviceBatteryLevelDidChangeNotification 常量传递给“name”参数，而不是字符串。它应该看起来像这样(注意缺少双引号):

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(batteryChanged:) name:UIDeviceBatteryLevelDidChangeNotification object:device];

(也有可能 UIDevice 根本不在后台发送这些通知。)