每隔几秒自动刷新或更新内容页面

Question

我正在使用Xamarin.forms(PCL),我需要每隔几秒刷新/更新内容页面及其数据.该数据是从检索API的viewmodel.

有没有可以定期使用的调用任何方法或处理Get Api周期里面page.xaml.cs,是这样的:

methodRunPeriodically()
{
 userdata = await UserService.GetUserasync(_UserViewModel.EmployeeId);
}

Answer 1

Xamarin.Forms有一个用于启动计时器的API,您可能会发现它对此有用,在此处记录.

Device.StartTimer (TimeSpan.FromSeconds(10), () => {
    // If you want to update UI, make sure its on the on the main thread.
    // Otherwise, you can remove the BeginInvokeOnMainThread
    Device.BeginInvokeOnMainThread(() => methodRunPeriodically());
    return shouldRunAgain;
});

Answer 2

根据上述问题中的代码,您将确保:

1. 您的userdata对象实现IPropertyChange,如下所示:

   //Other usings skipped for brevity
   ...
   ...
   using System.ComponentModel;
   using System.Runtime.CompilerServices;
   
   // This is a simple user class that 
   // implements the IPropertyChange interface.
   public class DemoUser : INotifyPropertyChanged
   {
       // These fields hold the values for the public properties.
       private string userName = string.Empty;
       private string phoneNumber = string.Empty;
   
       public event PropertyChangedEventHandler PropertyChanged;
   
       // This method is called by the Set accessor of each property.
       // The CallerMemberName attribute that is applied to the optional propertyName
       // parameter causes the property name of the caller to be substituted as an argument.
       private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
       {
           if (PropertyChanged != null)
           {
               PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
           }
       }
   
       public DemoUser()
       {
       }
       public string Id { get; set; }
       public string UserName
       {
           get
           {
               return this.userName;
           }
   
           set
           {
               if (value != this.userName)
               {
                   this.userName = value;
                   NotifyPropertyChanged();
               }
           }
       }
   
       public string PhoneNumber
       {
           get
           {
               return this.phoneNumber;
           }
   
           set
           {
               if (value != this.phoneNumber)
               {
                   this.phoneNumber = value;
                   NotifyPropertyChanged();
               }
           }
       }
   }
   

2. 在您的ContentPage中,然后尝试以下操作(我稍微修改了上面的其他代码):

   public class UserPage : ContentPage
   {
       private DemoUser demoUser;
       private int intervalInSeconds;
   
       public UserPage()
       {
           //Assuming this is a XAML Page....
           InitializeComponent();
       }
       public UserPage(DemoUser demoUser, int intervalInSeconds = 10) : this()
       {
           this.demoUser = demoUser;
           this.intervalInSeconds = intervalInSeconds;
   
           this.BindingContext = this.demoUser; 
   
           Device.StartTimer(TimeSpan.FromSeconds(this.intervalInSeconds), () =>
           {
               Device.BeginInvokeOnMainThread(() => refreshDemoUser());
               return true;
           });
       }
   
       private async void refreshDemoUser()
       {
           this.demoUser = await getDemoUserById(this.demoUser.Id);
       }
   }