问题描述
所以我是 xamarin 表单的新手，我的列表视图有问题。所以这是我的代码。
XML：
<RefreshView x:Name="MyContactRefreshView">
<ListView x:Name="MyContactList"
Margin="5"
ItemsSource="{Binding GroupedData}"
IsGroupingEnabled="True"
GroupdisplayBinding="{Binding Key}"
HasUnevenRows="True"
ItemTapped="GoToContactDetail"
>
<ListView.ItemTemplate>
<DataTemplate>
<TextCell Text="{Binding Name}" Detail="{Binding Phone1}" x:Name="ContactItem"/>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</RefreshView>
public partial class ContactList : ContentPage
{
private readonly ContactListGroupingviewmodel _contacts;
private bool _myContactListItemSourceIsBound;
public ICommand RefreshCommand { get { return new Command(async() => await RefreshList()); } }
public ContactList()
{
InitializeComponent();
_contacts = new ContactListGroupingviewmodel();
MyContactRefreshView.Command = RefreshCommand;
MyContactRefreshView.IsRefreshing = App.viewmodel.isBusy;
_myContactListItemSourceIsBound = false;
}
protected override void OnAppearing()
{
MyContactRefreshView.IsRefreshing = true;
base.OnAppearing();
}
private void GoToContactDetail(object sender,ItemTappedEventArgs e)
{
new DataLayer.Cummon.Commands.NavigatetoContactCommand().Execute(e.Item as ContactObservableModel);
}
public async Task RefreshList()
{
MyContactRefreshView.IsRefreshing = true;
MyContactList.SelectedItem = null;
await _contacts.RefreshList();
if (_myContactListItemSourceIsBound == false)
{
MyContactList.ItemsSource = _contacts.GroupedData;
_myContactListItemSourceIsBound = true;
}
MyContactRefreshView.IsRefreshing = false;
}
}
所以问题是我有这个按字母顺序排列的联系人列表视图。我有这个添加按钮，可以导航到联系人添加或编辑页面，添加联系人后，它会再次返回到此页面。因此，在返回此页面后，它不会更新列表。我一直在寻找几天。我在所有对象中都实现了 INotifyPropertyChanged。我所有的集合都是 Observable 的，正如你所看到的，我也尝试过 RefreshView。我用断点检查了我的整个代码，我发现除了我的列表之外一切正常。问题是更新的数据在那里，更新的数据绑定到 MyContactList.ITemSource 但我的列表不会更新，直到我关闭页面并再次打开它。是因为 OnAppearing() 事件吗？请帮帮我:(
抱歉，我的代码现在一团糟，因为我一直在尝试我在互联网上找到的所有内容。
编辑：这是我向我的列表添加联系人的方式：
<ContentPage.toolbaritems>
<ToolbarItem Text="افزودن مخاطب" IconImageSource="AddIcon.png" Command="{StaticResource NavigatetoContactAddOrEditPageCommand}" Order="Primary"/>
</ContentPage.toolbaritems>
public class NavigatetoContactAddOrEditPageCommand : ICommand
{
public event EventHandler CanExecuteChanged;
public bool CanExecute(object parameter)
{
return true;
}
public void RaiseCanExecuteChanged()
{
var handler = CanExecuteChanged;
if (handler != null)
{
handler(this,EventArgs.Empty);
}
}
public void Execute(object parameter)
{
NavigateAsync();
}
public async void NavigateAsync()
{
await App.MainNavigation.PushAsync(new Pages.ContactAddOrEditPage(),true);
}
}
在该页面中，我有条目可以输入数据，然后是另一个工具栏项来添加联系人
<ContentPage.toolbaritems>
<ToolbarItem IconImageSource="SubmitIcon.png" Text="ثبت" Order="Primary" Clicked="AddOrEditButton"/>
</ContentPage.toolbaritems>
点击时发生
private void AddOrEditButton(object sender,EventArgs e)
{
ContactObservableModel target = new ContactObservableModel()
{
Name = contactName.Text,Phone1 = contactPhone1.Text,Phone2 = contactPhone2.Text,AccountNumber = contactAccountNumber.Text,Phonesocial = contactPhone2.Text
};
new DataLayer.Cummon.Commands.AddToContactsCommand().Execute(target);
}
命令是
public class AddToContactsCommand : ICommand
{
private bool _isBusy = false;
public event EventHandler CanExecuteChanged;
public bool CanExecute(object parameter)
{
return !_isBusy;
}
public void RaiseCanExecuteChanged()
{
var handler = CanExecuteChanged;
if (handler != null)
{
handler(this,EventArgs.Empty);
}
}
public void Execute(object parameter)
{
AddToContacts(parameter as ContactObservableModel);
App.MainNavigation.PopAsync();
}
public async void AddToContacts(ContactObservableModel contact)
{
this._isBusy = true;
this.RaiseCanExecuteChanged();
App.viewmodel.isBusy = true;
await App.viewmodel.ContactListAsync.AddAsync(contact);
this._isBusy = false;
this.RaiseCanExecuteChanged();
App.viewmodel.isBusy = false;
}
}
public async Task RefreshList()
{
this.Items.Clear();
this.GroupedData.Clear();
await App.viewmodel.GetContactsItemsAsync();
var contacts = App.viewmodel.ContactListAsync.OrderBy(n => n.Name).ToList();
foreach (var contact in contacts)
{
this.Items.Add(contact);
}
var groupedContacts = Items.OrderBy(p => p.Name)
.GroupBy(p => p.Name[0].ToString())
.Select(p => new ObservableGroupCollection<string,ContactObservableModel>(p)).ToList();
foreach (var contact in groupedContacts)
{
this.GroupedData.Add(contact);
}
}
并且列表绑定到 GroupedData 属性。 我的 ContactGroupingviewmodel 上的 RefreshList 方法是这个
class ContactListGroupingviewmodel : ObservableBase
{
public ContactListGroupingviewmodel()
{
Items = new ObservableCollection<ContactObservableModel>();
GroupedData = new List<ObservableGroupCollection<string,ContactObservableModel>>();
}
public async Task RefreshList()
{
this.Items.Clear();
this.GroupedData.Clear();
await App.viewmodel.GetContactsItemsAsync();
var contacts = App.viewmodel.ContactListAsync.OrderBy(n => n.Name).ToList();
foreach (var contact in contacts)
{
this.Items.Add(contact);
}
var groupedContacts = Items.OrderBy(p => p.Name)
.GroupBy(p => p.Name[0].ToString())
.Select(p => new ObservableGroupCollection<string,ContactObservableModel>(p)).ToList();
foreach (var contact in groupedContacts)
{
this.GroupedData.Add(contact);
}
}
private IList<ContactObservableModel> _items;
public IList<ContactObservableModel> Items
{
get { return _items; }
set { this.SetProperty(ref this._items,value); }
}
private List<ObservableGroupCollection<string,ContactObservableModel>> _groupedData;
public List<ObservableGroupCollection<string,ContactObservableModel>> GroupedData
{
get { return _groupedData; }
set { this.SetProperty(ref this._groupedData,value); }
}
}
解决方法
您需要使用 ObservableCollection 将任何更改通知 ListView。
来自document：
如果您希望 ListView 在添加项目时自动更新，
在基础列表中删除和更改，您需要使用
ObservableCollection。 ObservableCollection 定义在
System.Collections.ObjectModel 和 List 一样，除了它
可以通知 ListView 任何更改：
ObservableCollection<Employee> employees = new ObservableCollection<Employee>();
listView.ItemsSource = employees;
//Mr. Mono will be added to the ListView because it uses an ObservableCollection
employees.Add(new Employee(){ DisplayName="Mr. Mono"});