删除记录后，我很难刷新Xamarin ListView，或者从其他视图添加了一个。
我有一个视图（RaceList.xaml），它列出了从ViewModel获取的可观察集合中的种族。
RaceList.xaml.cs
using System.Collections.Generic;
using TechsportiseApp.API;
using TechsportiseApp.API.Models;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using TechsportiseApp.MainUI.ViewModels;
using System;
namespace TechsportiseApp.MainUI
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class RaceList : ContentPage
{
public List<Race> Races { get; set; }
public RaceList()
{
InitializeComponent();
var viewModel = new RaceListViewModel();
BindingContext = viewModel;
ToolbarItems.Add(new ToolbarItem("New", "Add.png", async () =>
{
await Navigation.PushAsync(new RaceNew());
}));
}
public void OnDelete(object sender, EventArgs e)
{
var menuitem = ((MenuItem)sender);
var stringraceid = menuitem.CommandParameter.ToString();
int raceid = Int32.Parse(stringraceid);
RacesAPI.DeleteRace(raceid);
MessagingCenter.Send(this, "RaceListChanged");
}
protected override void OnAppearing()
{
base.OnAppearing();
RacesAPI.GetRaces();
//LoadServerRegisteredCitizen is a method which i used to load items inside the listview
}
async void Handle_ItemTapped(object sender, Xamarin.Forms.ItemTappedEventArgs e)
{
if (e.Item == null)
return;
var race = e.Item as Race;
await Navigation.PushAsync(new RaceView(race));
//Deselect Item
((ListView)sender).SelectedItem = null;
}
}
}
RaceList.xaml
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="TechsportiseApp.MainUI.RaceList"
Title="Races">
<!--SelectedItem="{Binding RaceSelected, Mode=TwoWay} "-->
<ListView ItemsSource="{Binding Races}"
ItemTapped="Handle_ItemTapped"
SeparatorVisibility = "None"
IsPullToRefreshEnabled="true"
RefreshCommand="{Binding RefreshCommand}"
IsRefreshing="{Binding IsBusy}">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<ViewCell.ContextActions>
<MenuItem Clicked="OnDelete" CommandParameter="{Binding Id}" Text="Delete" IsDestructive="True" />
</ViewCell.ContextActions>
<StackLayout>
<Label Text="{Binding Name}" />
<Label Text="{Binding RaceDate}" />
<BoxView Color="#B2B2B2" HeightRequest="1" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</ContentPage>
RaceListViewModel.cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Threading.Tasks;
using Newtonsoft.Json;
using RestSharp;
using TechsportiseApp.API.Models;
using Xamarin.Forms;
using TechsportiseApp.API;
using System.Windows.Input;
using System.Collections.ObjectModel;
namespace TechsportiseApp.MainUI.ViewModels
{
public class RaceListViewModel : INotifyPropertyChanged
{
public RaceListViewModel()
{
_refreshCommand = new Command(RefreshList);
MessagingCenter.Subscribe<RaceListViewModel>(this, "RaceListChanged", sender => {
Races = RacesAPI.GetRaces();
OnPropertyChanged("Id");
});
}
public void RefreshList()
{
//Refreshes list on Pull to Refresh
Races = RacesAPI.GetRaces();
}
int _id;
public int Id
{
get
{
return _id;
}
set
{
if (_id != value)
{
_id = value;
// trigger some action to take such as updating other labels or fields
OnPropertyChanged("Id");
}
}
}
int _name;
public int Name
{
get
{
return _name;
}
set
{
if (_name != value)
{
_name = value;
// trigger some action to take such as updating other labels or fields
OnPropertyChanged("Name");
}
}
}
private ObservableCollection<Race> _races;
public ObservableCollection<Race> Races
{
get
{
var racelist = RacesAPI.GetRaces();
IsBusy = false;
return racelist;
}
set
{
if (_races != value)
{
_races = value;
// trigger some action to take such as updating other labels or fields
OnPropertyChanged("Races");
}
}
}
private Race _raceSelected;
public Race RaceSelected
{
get
{
return RaceSelected;
}
set
{
if (RaceSelected != value)
{
RaceSelected = value;
OnPropertyChanged("RaceSelected");
}
}
}
private bool _isBusy;
public bool IsBusy
{
get { return _isBusy; }
set
{
if (_isBusy == value)
return;
_isBusy = value;
OnPropertyChanged("IsBusy");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
var changed = PropertyChanged;
if (changed != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
Command _refreshCommand;
public Command RefreshCommand
{
get
{
return _refreshCommand;
}
}
}
}
按下工具栏中的“创建”按钮，这会将我带到一个新的视图，该视图显示一个空白表单，允许我填写新竞赛的数据。如果这是Saved，它会将JSON推送到我的API，如果成功，它会将它们重定向到编辑页面。
RaceNew.xaml
<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
x:Class="TechsportiseApp.MainUI.RaceNew"
Title="New Race">
<ContentPage.Content>
<ScrollView Orientation = "Vertical" VerticalOptions="StartAndExpand">
<StackLayout Padding="0,20,0,0">
<Label x:Name="labelName" Text="Name" />
<Entry x:Name="entryName" />
<Label x:Name="labelDescription" Text="Description" />
<Editor x:Name="editorDescription" />
<Label x:Name="labelContactName" Text="Contact Name" />
<Entry x:Name="entryContactName" />
<Label x:Name="labelContactNumber" Text="Contact Number" />
<Entry x:Name="entryContactNumber" Keyboard="Telephone" />
<Label x:Name="labelContactEmail" Text="ContactEmail" />
<Entry x:Name="entryContactEmail" Keyboard="Email" />
<Label x:Name="labelRaceDate" Text="Race Date" />
<DatePicker x:Name="datepickerRaceDate" Date="{Binding Source={x:Static sys:DateTime.Now}" Format="ddd d MMMM yyyy" />
<Label x:Name="labelRaceStartTime" Text="Race Time" />
<TimePicker x:Name="timepickerRaceStartTime" />
<Label x:Name="labelMaxEntries" Text="Max Entries" />
<Entry x:Name="entryMaxEntries" Keyboard="Numeric" />
<Label x:Name="labelCurrentEntries" Text="Current Entries" />
<Entry x:Name="entryCurrentEntries" Keyboard="Numeric" />
<Label x:Name="labelIsOpenForEntries" Text="Open For Entries" />
<Switch x:Name="switchIsOpenForEntries" />
<Label x:Name="labelIsPublished" Text="Published" />
<Switch x:Name="switchIsPublished" />
</StackLayout>
</ScrollView>
</ContentPage.Content>
</ContentPage>
RaceNew.xaml.cs
using System;
using TechsportiseApp.API;
using TechsportiseApp.API.Models;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
namespace TechsportiseApp.MainUI
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class RaceNew : ContentPage
{
public RaceNew()
{
InitializeComponent();
ToolbarItems.Add(new ToolbarItem("Create", "", async () =>
{
var saverace = new Race();
saverace.ContactEmail = entryContactEmail.Text;
saverace.ContactName = entryContactName.Text;
saverace.ContactNumber = entryContactNumber.Text;
saverace.CurrentEntries = 0;
saverace.Description = editorDescription.Text;
saverace.IsOpenForEntries = switchIsOpenForEntries.IsToggled;
saverace.IsPublished = switchIsPublished.IsToggled;
saverace.IsComplete = false;
saverace.MaxEntries = System.Convert.ToInt32(entryMaxEntries.Text);
saverace.Name = entryName.Text;
saverace.RaceDate = datepickerRaceDate.Date;
var timestring = string.Format("{0:00}:{1:00}:{2:00}", timepickerRaceStartTime.Time.Hours, timepickerRaceStartTime.Time.Minutes, timepickerRaceStartTime.Time.Seconds);
saverace.RaceStartTime = timestring;
var response = RacesAPI.CreateRace(saverace);
if (response.Code == "Created")
{
saverace.Id = response.ReturnedId;
Navigation.InsertPageBefore(new RaceView(saverace), this);
await Navigation.PopAsync();
}
//Error response
else
{
await DisplayAlert("Error: " + response.Code, "There has been an error creating your race. " + response.Content, "OK");
}
}));
}
async void OnBackButtonClicked(object sender, EventArgs e)
{
await Navigation.PopAsync();
}
}
}
在此页面中，我只需按“返回”按钮即可返回我的RaceList视图。
问题是，列表视图没有刷新 - 它没有注册添加新种族。
此外，在我的RaceList.xaml.cs中，您可以看到我还有一个正在使用的删除按钮。当我从列表中删除项目时，它也不会刷新！
有什么想法吗？
答案 0 :(得分：1)
覆盖Xamarin.Forms.Page.OnAppearing方法并调用ViewModel的RefreshList（）方法。
RacelistViewModel Viewmodel =（RaceListViewModel）This.DataContext; ViewModel.RefreshList（）;
答案 1 :(得分：0)
我不知道，但是
public List<Race> Races { get; set; }
是List，而不是ObservableCollection。