Xamarin MVVM 从另一个页面删除 Listview 项目
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【中文标题】Xamarin MVVM 从另一个页面删除 Listview 项目【英文标题】：Xamarin MVVM Delete Listview Item from Another Page 【发布时间】：2020-02-07 03:46:12 【问题描述】：您好，Xamarin 表单的新手。我有一个列表视图，我可以在选择项目时提取信息，类似于 Visual Studio 2017 xamarin 项目中提供的模板。
希望模板更完整，因为添加和更新效果很好，但我在创建删除方法时遇到了麻烦。数据已从 SQLite 中删除，但 ObservableCollection 不会刷新。
我尝试将类似的逻辑从添加和更新复制到删除。我尝试将另一个消息中心方法添加到我的构造函数中，但是在添加调试等调试时它没有被击中。不知道我错过了什么。还在我头上。
这是列表视图，它工作得很好
<ContentPage.ToolbarItems>
<ToolbarItem Text="-" Command="Binding ExecuteDeleteAllCommand"></ToolbarItem>
<ToolbarItem Text="+" Clicked="InsertAuditClicked"></ToolbarItem>
</ContentPage.ToolbarItems>
<ContentPage.Padding>
<OnIdiom>10, 10, 10, 10</OnIdiom>
</ContentPage.Padding>
<ContentPage.Content>
<StackLayout>
<ListView x:Name="AuditsListView"
ItemsSource="Binding AuditsCollection"
VerticalOptions="FillAndExpand"
HasUnevenRows="true"
RefreshCommand="Binding LoadAuditsCommand"
IsPullToRefreshEnabled="true"
IsRefreshing="Binding IsBusy, Mode=OneWay"
CachingStrategy="RecycleElement"
ItemSelected="OnAuditSelected">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Grid>
<StackLayout Grid.Column="0">
<!-- <Label Text="Binding Id"
LineBreakMode="NoWrap"
Style="DynamicResource ListAuditTextStyle"
FontSize="16"></Label>-->
<Label Text="Binding AuditId"
Style="DynamicResource ListAuditTextStyle"
FontSize="16"></Label>
<Label Text="Binding AuditCommand"
LineBreakMode="NoWrap"
Style="DynamicResource ListAuditDetailTextStyle"
FontSize="13"></Label>
</StackLayout>
<StackLayout Grid.Column="1" VerticalOptions="CenterAndExpand" HorizontalOptions="EndAndExpand">
<Label Text=">" FontSize="18"></Label>
</StackLayout>
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage.Content>
这里是代码
AuditsViewModel ViewModel;
public AuditsPage()
InitializeComponent();
BindingContext = ViewModel = new AuditsViewModel();
async void OnAuditSelected(object s, SelectedItemChangedEventArgs e)
var m = e.SelectedItem as AuditModel;
if (m == null)
return;
await Navigation.PushAsync(new AuditDetailPage(new AuditDetailViewModel(m))); // (new AuditDetailPage(new AuditDetailViewModel(m)));
AuditsListView.SelectedItem = null;
async void InsertAuditClicked(object sender, EventArgs e)
await Navigation.PushModalAsync(new NavigationPage(new AuditNewPage()));
protected override void OnAppearing()
base.OnAppearing();
if (ViewModel.AuditsCollection.Count == 0)
ViewModel.LoadAuditsCommand.Execute(null);
这是视图模型
namespace AuditTest.ViewModels
public class AuditsViewModel : BaseViewModel
public ObservableCollection<AuditModel> AuditsCollection get; set;
public Command LoadAuditsCommand get; set;
public AuditsViewModel()
Title = "Browse";
AuditsCollection = new ObservableCollection<AuditModel>();
LoadAuditsCommand = new Command(async () => await ExecuteLoadAuditsCommand());
MessagingCenter.Subscribe<AuditNewPage, AuditModel>(this, "AddAudit", async (o, a) =>
var n = a as AuditModel;
AuditsCollection.Add(n);
await App.MobileDataBase.InsertAuditAsync(n);
);
//MessagingCenter.Subscribe<AuditDetailPage, AuditModel>(this, "DeleteAudit", async (o, a) =>
//
// var n = a as AuditModel;
// AuditsCollection.Remove(n);
// await App.MobileDataBase.DeleteAuditAsync(n);
//);
async Task ExecuteLoadAuditsCommand()
if (IsBusy)
return;
IsBusy = true;
try
AuditsCollection.Clear();
var a = await App.MobileDataBase.GetAuditsAsync(true); // var a = await DataSource.GetAuditsAsync(true);
foreach (var i in a)
AuditsCollection.Add(i);
catch (Exception ex)
Debug.WriteLine(ex);
finally
IsBusy = false;
有一个带有点击事件的工具栏。这是后面的代码
using AuditTest.Models;
using Xamarin.Forms;
using AuditTest.Views;
using System.Threading.Tasks;
namespace AuditTest.ViewModels
public class AuditDetailViewModel : BaseViewModel
public AuditModel AuditDetail get; set;
public AuditDetailViewModel(AuditModel m = null)
Title = m.AuditId.ToString(); // m?.AuditId;
AuditDetail = m;
public Command ExecuteEditAuditCommand
get
return new Command(async () =>
await DataSource.UpdateAuditAsync(AuditDetail);
);
public Command ExecuteDeleteAuditCommand
get
return new Command(async () =>
await App.MobileDataBase.DeleteAuditAsync(AuditDetail); // DataSource.DeleteAuditAsync(AuditDetail.AuditId));
);
public Task TestUpdateCommand()
Task<bool> tt = App.MobileDataBase.UpdateAuditAsync(AuditDetail);
return tt;
public Task TestDeleteCommand()
Task<bool> tt = App.MobileDataBase.DeleteAuditAsync(AuditDetail);
MessagingCenter.Send(this, "DeleteAudit", this.AuditDetail); // await ViewModel.ExecuteDeleteAuditCommand(); // App.MobileDataBase.DeleteAuditAsync();
return tt;
使用不同的属性和方法，但这里是内容页面的视图模型
using AuditTest.Models;
using Xamarin.Forms;
using AuditTest.Views;
using System.Threading.Tasks;
namespace AuditTest.ViewModels
public class AuditDetailViewModel : BaseViewModel
public AuditModel AuditDetail get; set;
public AuditDetailViewModel(AuditModel m = null)
Title = m.AuditId.ToString(); // m?.AuditId;
AuditDetail = m;
public Command ExecuteEditAuditCommand
get
return new Command(async () =>
await DataSource.UpdateAuditAsync(AuditDetail);
);
public Command ExecuteDeleteAuditCommand
get
return new Command(async () =>
await App.MobileDataBase.DeleteAuditAsync(AuditDetail); // DataSource.DeleteAuditAsync(AuditDetail.AuditId));
);
public Task TestUpdateCommand()
Task<bool> tt = App.MobileDataBase.UpdateAuditAsync(AuditDetail);
return tt;
public Task TestDeleteCommand()
Task<bool> tt = App.MobileDataBase.DeleteAuditAsync(AuditDetail);
MessagingCenter.Send(this, "DeleteAudit", this.AuditDetail); // await ViewModel.ExecuteDeleteAuditCommand(); // App.MobileDataBase.DeleteAuditAsync();
return tt;
【问题讨论】：
DeleteAudit 消息是从 AuditDetailViewModel 发送的，所以对应的订阅也需要从 AuditDetailViewModel 监听表单消息，而不是 AuditDetailPage 【参考方案1】：已修复。谢谢杰森，你太棒了！现在可以了。
取消注释并更改 ViewModel 构造函数上的消息中心订阅以指向另一个 ViewModel 发送
MessagingCenter.Subscribe<AuditDetailViewModel, AuditModel>(this, "DeleteAudit", async (o, a) =>
var n = a as AuditModel;
AuditsCollection.Remove(n);
await App.MobileDataBase.DeleteAuditAsync(n);
);
其他ViewModel上的Public Method还有这个
public void MethodDeleteCommand()
MessagingCenter.Send(this, "DeleteAudit", this.AuditDetail);
【讨论】：
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