iOS MultiTasking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;
}

由于某些原因，通知没有被遵守。我做错了什么吗？我想在拔下电源后观察10分钟

Answer 1

您不应该在buttonPressed:方法中调用endBackgroundUpdateTask，因为这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(注意没有双引号)：

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

(也有可能UIDevice根本不会在后台发送这些通知。)

Answer 2

您是否已将适用的背景代码添加到您的AppDelegate？下面是《iOS编程指南》中的背景instructions