电池状态获取（UIDevice、battery、UIDeviceBattery）

    //通过UIDevice类，可以取得电池剩余量以及充电状态的信息，首先需要设置batteryMonitoringEnabled为YES
    UIDevice * device = [UIDevice currentDevice];
    device.batteryMonitoringEnabled = YES;
    
    //0.0-1.0取得失败的适合为-1.0
    NSLog(@"%f", device.batteryLevel);
    
    /*
     typedef NS_ENUM(NSInteger, UIDeviceBatteryState) {
     UIDeviceBatteryStateUnknown,
     UIDeviceBatteryStateUnplugged,   // on battery, discharging
     UIDeviceBatteryStateCharging,    // plugged in, less than 100%
     UIDeviceBatteryStateFull,        // plugged in, at 100%
     };              // available in iPhone 3.0
     
     UIDeviceBatteryStateUnknown：无法取得充电状态情况
     UIDeviceBatteryStateUnplugged：非充电状态
     UIDeviceBatteryStateCharging：充电状态
     UIDeviceBatteryStateFull：充满状态（连接充电器充满状态）
     */
    NSLog(@"%ld", (long)device.batteryState);
    
    
    //监视电池剩余电量
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(action1:) name:UIDeviceBatteryLevelDidChangeNotification object:nil];
    
    //监视充电状态
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(action2:) name:UIDeviceBatteryStateDidChangeNotification object:nil];