ComboBox 上的 SelectedItem [英] SelectedItem on ComboBox

问题描述

应用程序中有一个 ComboBox 绑定到一组项目.在某些情况下，用户可以从 ComboBox 中选择一个项目，但所选项目可能尚未准备好，因此 ComboBox 所选项目必须回到上一个所选项目(或集合中的其他一些项目)，但在当前应用程序中 ComboBox 总是显示来自用户的选定项目，而不是在将其设置回并调用通知属性更改后检索有效项目.

There is a ComboBox in the application which is bound to a collection of items. There are cases that user can select an item from the ComboBox but the selected item might not be ready yet so the ComboBox selected item must get back to the previous selected item (or some other item in the collection), but in the current application ComboBox always shows the selected item from the user instead of retrieving the valid item after setting it back and calling notify property change.

流程是一个简化的代码，它显示了问题.

The flowing is a simplified code of which shows the problem.

public partial class MainWindow : Window, INotifyPropertyChanged
{
    private List<Customer> _Customers = new List<Customer>();

    public List<string> CustomerNames
    {
        get
        {
            var list = new List<string>();
            foreach (var c in _Customers)
            {
                list.Add(c.Name);
            }
            return list; ;
        }
    }

    public string CustomerName
    {
        get
        {
            var customer = _Customers.Where(c => c.IsReady).FirstOrDefault();
            return customer.Name;
        }
        set
        {
            NotifyPropertyChanged("CustomerName");
        }
    }

    public MainWindow()
    {
        SetupCustomers();
        InitializeComponent();
        this.DataContext = this;
    }

    private void SetupCustomers()
    {
        _Customers.Add(new Customer("c1", true));
        _Customers.Add(new Customer("c2", false));
        _Customers.Add(new Customer("c3", false));
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class Customer
{
    public Customer(string name, bool isReady)
    {
        this.Name = name;
        this.IsReady = isReady;
    }

    public bool IsReady { get; set; }

    public string Name { get; set; }

    public override bool Equals(object obj)
    {
        return base.Equals(obj);
    }
    public override int GetHashCode()
    {
        return base.GetHashCode();
    }
}    


<Window x:Class="TryComboboxReset.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<Grid>

    <ComboBox   Width="100"
                Height="25"
                ItemsSource="{Binding Path=CustomerNames, Mode=OneWay}"
                SelectedItem="{Binding Path=CustomerName, Mode=TwoWay}"/>

</Grid>

推荐答案

问题是UI线程，我用dispatcher解决了这个问题

The problem was UI thread, I used dispatcher to fix this problem

 public partial class MainWindow : Window, INotifyPropertyChanged
{
    private ObservableCollection<Customer> _Customers =
        new ObservableCollection<Customer>();

    public ObservableCollection<Customer> CustomerNames
    {
        get
        {
            return _Customers;
        }
    }

    public Customer CustomerName
    {
        get
        {
            return _Customers.Where(c => c.IsReady == true).FirstOrDefault();
        }
        set
        {
            // Delay the revert
            Application.Current.Dispatcher.BeginInvoke(
                new Action(() => NotifyPropertyChanged("CustomerName")), DispatcherPriority.ContextIdle, null);
        }
    }

    public MainWindow()
    {
        SetupCustomers();
        InitializeComponent();
        this.DataContext = this;
    }

    private void SetupCustomers()
    {
        _Customers.Add(new Customer("c1", true));
        _Customers.Add(new Customer("c2", false));
        _Customers.Add(new Customer("c3", false));
        CustomerName = _Customers.Where(c => c.IsReady == true).FirstOrDefault();
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class Customer
{
    public Customer(string name, bool isReady)
    {
        this.Name = name;
        this.IsReady = isReady;
    }

    public bool IsReady { get; set; }

    public string Name { get; set; }
}   

<ComboBox   Width="400"
            Height="25"
            ItemsSource="{Binding Path=CustomerNames}"
            SelectedValue="{Binding CustomerName,Mode=TwoWay}"    >
       <ComboBox.ItemTemplate>
             <DataTemplate>
                 <TextBlock Text="{Binding Name}"/>
             </DataTemplate>
        </ComboBox.ItemTemplate>
 </ComboBox>

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