iOS开发——应用图标上显示消息数量

　　iOS8以前：

UIApplication *app = [UIApplication sharedApplication];

app.applicationIconBadgeNumber = num;

　　iOS8及以后：

UIUserNotificationSettings *settings = [UIUserNotificationSettings settingsForTypes:UIUserNotificationTypeBadge categories:nil];

[[UIApplication sharedApplication] registerUserNotificationSettings:settings];

　　需要先设置它，才行。而且，需要注意一点，iOS8以前，不能带它，iOS8及以后必须带它。

　　所以现在再用它的时候，需要先判断系统版本号：

float version = [[[UIDevice currentDevice] systemVersion] floatValue];

if (version >= 8.0) {

　　 UIUserNotificationSettings *settings = [UIUserNotificationSettings settingsForTypes:UIUserNotificationTypeBadge categories:nil];

　　[[UIApplication sharedApplication] registerUserNotificationSettings:settings];

}