所选项目在选取器中不起作用

Question

在我们的编辑页面中，我们有一个问题，即在选择器中将值填充到选定项中，并且由于某种原因，它也不会从 LoadCourses() 或 LoadRoundCategories() 中进行选择。

有什么想法吗？

代码如下：

视图模型

public class EditGolfRoundViewModel : INotifyPropertyChanged
{
ApiServices _apiServices = new ApiServices();
private string _message;
private ObservableCollection<GolfCourse> _courses;
private ObservableCollection<GolfRoundCategory> _roundCategories;
private object_selectedGolfCourse;
private GolfRoundCategory _selectedGolfRoundCategory;
private GolfRound _golfRound;
public EditGolfRoundViewModel()
{
_selectedGolfCourse = new GolfCourse();
_selectedGolfRoundCategory = new GolfRoundCategory();
LoadCourses();
LoadRoundCategories();
}
public GolfRound GolfRound
{
get { return _golfRound; }
set
{
_golfRound = value;
OnPropertyChanged();
}
}

public string Message
{
get { return _message; }
set
{
_message = value;
OnPropertyChanged();
}
}
public ObservableCollection<GolfCourse> GolfCourses
{
get { return _courses; }
set
{
if (_courses != value)
{
_courses = value;
OnPropertyChanged();
}
}
}
public ObservableCollection<GolfRoundCategory> GolfRoundCategories
{
get { return _roundCategories; }
set
{
_roundCategories = value;
OnPropertyChanged();
}
}
public object SelectedGolfCourse
{
get { return _selectedGolfCourse; }
set
{
_selectedGolfCourse = value;
var golfCourse = _selectedGolfCourse as GolfCourse;
Guid tempGolfCourseID = golfCourse.GolfCourseID;
OnPropertyChanged("SelectedGolfCourse");
}
}

public GolfRoundCategory SelectedGolfRoundCategory
{
get { return _selectedGolfRoundCategory; }
set
{
_selectedGolfRoundCategory = value;
OnPropertyChanged();
}
}

public ICommand EditCommand 
{ 
get
{
return new Command(async() =>
{
GolfRound.GolfCourseID = SelectedGolfCourse.GolfCourseID;
GolfRound.GolfCourse = SelectedGolfCourse;
GolfRound.GolfRoundCategoryID = SelectedGolfRoundCategory.GolfRoundCategoryID;
GolfRound.GolfRoundCategory = SelectedGolfRoundCategory;
GolfRound.LastModifiedUTC = System.DateTime.Now;
await _apiServices.PutGolfRoundAsync(GolfRound, Settings.AccessToken);
});
}
}
public ICommand DeleteCommand
{
get
{
return new Command(async () =>
{
await _apiServices.DeleteGolfRoundAsync(GolfRound.GolfRoundID, Settings.AccessToken);
});
}
}
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
private async void LoadCourses()
{
GolfCourses = new ObservableCollection<GolfCourse>(await _apiServices.GetGolfCoursesAsync(Settings.AccessToken));
}
private async void LoadRoundCategories()
{
GolfRoundCategories = new ObservableCollection<GolfRoundCategory>(await _apiServices.GetGolfRoundCategoriesAsync(Settings.AccessToken));
}
}

视图 - XAML

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:viewModels="clr-namespace:AthlosifyMobile.ViewModels.Golf"
x:Class="AthlosifyMobile.Views.EditGolfRoundPage">
<StackLayout Orientation="Vertical" VerticalOptions="Center" Spacing="30" Padding="30">
<Entry Text="{Binding GolfRound.Name}" Placeholder="name" FontSize="Default" />
<Entry Text="{Binding GolfRound.Notes}" Placeholder="notes" FontSize="Default" />
<Entry Text="{Binding GolfRound.DailyHandicap}" Placeholder="daily handicap" FontSize="Default" />
<Label Text="Date" />
<DatePicker Date="{Binding GolfRound.TeeOffUTC}" 
Format="D"
Margin="30, 0, 0, 30"  />
<Picker x:Name="pCourse" Title="Course" ItemsSource="{Binding GolfCourses}" 
SelectedItem="{Binding SelectedGolfCourse, Mode=TwoWay}" 
ItemDisplayBinding="{Binding Name}"></Picker>
<Entry Text="{Binding GolfRound.GolfCourse.Name}" Placeholder="selected golf course" FontSize="Default" />
<Picker x:Name="pCategory" Title="Category" ItemsSource="{Binding GolfRoundCategories}" 
SelectedItem="{Binding SelectedGolfRoundCategory, Mode=TwoWay}"
ItemDisplayBinding="{Binding Name}"></Picker>
<Entry Text="{Binding SelectedGolfRoundCategory.Name}" Placeholder="selected round category" FontSize="Default" />
<Button Command="{Binding EditCommand}" Text="Edit Round" />
<Button Command="{Binding DeleteCommand}" Text="Delete Round" />
<Label Text="{Binding Message}" ></Label>
</StackLayout>

视图 - 代码隐藏

public partial class EditGolfRoundPage : ContentPage
{
public EditGolfRoundPage (GolfRound round)
{
var editGolfRoundViewModel = new EditGolfRoundViewModel();
editGolfRoundViewModel.GolfRound = round;
BindingContext = editGolfRoundViewModel;
InitializeComponent ();
//var editGolfRoundViewModel = new EditGolfRoundViewModel();
//editGolfRoundViewModel.GolfRound = round;
//editGolfRoundViewModel.SelectedGolfCourse = round.GolfCourse;
//BindingContext = editGolfRoundViewModel;
}
}

Answer 1

为SelectedItem中使用的属性类实现IEquatable：

public class GolfCourse : IEquatable<GolfCourse>
{
...
public bool Equals(GolfCourse other)
{
if (other == null) return false;
return (this.Name.Equals(other.Name));
}
}

用法，假设ItemsSource包含值为Name的对象，如下所示：

SelectedGolfCourse = new GolfCourse { Name = "Course 2" };

Answer 2

以下情况适用于 Xamarin Forms v4.7。

查看您是否正在执行此操作：

<Picker x:Name="DefaultEntitlement" Title="Entitlement"
SelectedItem="{Binding SelectedOwnerEntitlement, Mode=TwoWay}"
ItemsSource="{Binding OwnerEntitlements, Mode=TwoWay}">
</Picker>

取而代之的是：

<Picker x:Name="DefaultEntitlement" Title="Entitlement"
ItemsSource="{Binding OwnerEntitlements, Mode=TwoWay}"
SelectedItem="{Binding SelectedOwnerEntitlement, Mode=TwoWay}">
</Picker>

Answer 3

您在初始化页面之前绑定视图模型，所以这是错误的事情，如果没有初始化页面，我们无法绑定数据，您需要更改 xaml 的代码.cs如下所示 public EditGolfRoundPage (GolfRound round) { InitializeComponent (); BindingContext = editGolfRoundViewModel; BindingContext.GolfRound = round; }

这将为你工作 快乐编码:)

Answer 4

Xaml

<Picker x:Name="ProductPicker" WidthRequest="220"    HeightRequest="35" Title="Select" ItemsSource="{Binding ProductList}" SelectedItem="{Binding ProductSelected}" ItemDisplayBinding="{Binding ProductName}">   </Picker>

视图模型

public List<ProductModel> ProductList { get; set; }

在视图模型中填充数据源中的数据

ProductList = Products.Result.ToList();

获取所选数据

private object _ProductSelected;
public object ProductSelected
{
get { return _ProductSelected; }
set
{
_ProductSelected = value;
ProductSelected_SelectedIndex.Execute(value);
OnPropertyChanged("ProductSelected"); //in case you are using MVVM Light
}
}
private Command ProductSelected_SelectedIndex
{
get
{
return new Command((e) =>
{

}}}

private object _CitySelectedFromList;
public object CitySelectedFromList
{
get { return _CitySelectedFromList; }
set
{
_CitySelectedFromList = value;
var cityid = _CitySelectedFromList as CityMasterModel;
tempcityids = Convert.ToInt32(cityid.Id);
}
}

Answer 5

您可以尝试一次替换视图模型吗？我已将类型从"对象"更改为"实际类型"。从端点加载项目时设置默认项目。

public class EditGolfRoundViewModel : INotifyPropertyChanged
{
ApiServices _apiServices = new ApiServices();
private string _message;
private ObservableCollection<GolfCourse> _courses;
private ObservableCollection<GolfRoundCategory> _roundCategories;
private GolfCourse _selectedGolfCourse;
private GolfRoundCategory _selectedGolfRoundCategory;
private GolfRound _golfRound;
public EditGolfRoundViewModel()
{
LoadCourses();
LoadRoundCategories();
}
public GolfRound GolfRound
{
get { return _golfRound; }
set
{
_golfRound = value;
OnPropertyChanged();
}
}

public string Message
{
get { return _message; }
set
{
_message = value;
OnPropertyChanged();
}
}
public ObservableCollection<GolfCourse> GolfCourses
{
get { return _courses; }
set
{
if (_courses != value)
{
_courses = value;
OnPropertyChanged();
}
}
}
public ObservableCollection<GolfRoundCategory> GolfRoundCategories
{
get { return _roundCategories; }
set
{
_roundCategories = value;
OnPropertyChanged();
}
}
public GolfCourse SelectedGolfCourse
{
get { return _selectedGolfCourse; }
set
{
_selectedGolfCourse = value;
OnPropertyChanged("SelectedGolfCourse");
}
}

public GolfRoundCategory SelectedGolfRoundCategory
{
get { return _selectedGolfRoundCategory; }
set
{
_selectedGolfRoundCategory = value;
OnPropertyChanged();
}
}

public ICommand EditCommand
{
get
{
return new Command(async () =>
{
GolfRound.GolfCourseID = SelectedGolfCourse.GolfCourseID;
GolfRound.GolfCourse = SelectedGolfCourse;
GolfRound.GolfRoundCategoryID = SelectedGolfRoundCategory.GolfRoundCategoryID;
GolfRound.GolfRoundCategory = SelectedGolfRoundCategory;
GolfRound.LastModifiedUTC = System.DateTime.Now;
await _apiServices.PutGolfRoundAsync(GolfRound, Settings.AccessToken);
});
}
}
public ICommand DeleteCommand
{
get
{
return new Command(async () =>
{
await _apiServices.DeleteGolfRoundAsync(GolfRound.GolfRoundID, Settings.AccessToken);
});
}
}
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
private async void LoadCourses()
{
GolfCourses = new ObservableCollection<GolfCourse>(await _apiServices.GetGolfCoursesAsync(Settings.AccessToken));
if (GolfCourses != null && GolfCourses.Count() > 0)
SelectedGolfCourse = GolfCourses[0];
}
private async void LoadRoundCategories()
{
GolfRoundCategories = new ObservableCollection<GolfRoundCategory>(await _apiServices.GetGolfRoundCategoriesAsync(Settings.AccessToken));
if (GolfRoundCategories != null && GolfRoundCategories.Count() > 0)
SelectedGolfRoundCategory = GolfRoundCategories[0];
}
}

Answer 6

你可以试试：

• 确保您的道具支撑INotifyPropertyChanged
• 确保变量Selected Item具有初始值
• 尝试调试您的selected item变量，确保具有值

1.缩写

看看你的代码：

public EditGolfRoundViewModel()
{
_selectedGolfCourse = new GolfCourse();
_selectedGolfRoundCategory = new GolfRoundCategory();
LoadCourses();
LoadRoundCategories();
}

如果您尝试初始值Selected Item，请不要这样做：

_selectedGolfCourse = new GolfCourse();
_selectedGolfRoundCategory = new GolfRoundCategory();

让它null，很好。你可以这样做：

SelectedGolfRoundCategory = new GolfRoundCategory();
//or
SelectedGolfRoundCategory = dataFromAPI;

2. 分配

看看你的代码：

public ICommand EditCommand 
{ 
get
{
return new Command(async() =>
{
GolfRound.GolfCourseID = SelectedGolfCourse.GolfCourseID;
GolfRound.GolfCourse = SelectedGolfCourse;
GolfRound.GolfRoundCategoryID = SelectedGolfRoundCategory.GolfRoundCategoryID;
GolfRound.GolfRoundCategory = SelectedGolfRoundCategory;
GolfRound.LastModifiedUTC = System.DateTime.Now;
await _apiServices.PutGolfRoundAsync(GolfRound, Settings.AccessToken);
});
}
}

您尝试将变量插入selected item对象GolfRound，就像这部分一样：

GolfRound.GolfRoundCategoryID = SelectedGolfRoundCategory.GolfRoundCategoryID;
GolfRound.GolfRoundCategory = SelectedGolfRoundCategory;

确保您INotifyPropertyChanged为道具GolfRoundCategoryID和GolfRoundCategory实现此模型GolfRound。否则，它将不起作用。我有这方面的经验。

希望这有帮助。