如何使用ComboBox的Text属性禁用ItemsSource同步 [英] How to disable ItemsSource synchronization with Text property of ComboBox

问题描述

我使用ComboBox绑定到视图模型的字符串属性。我选择ComboBox而不是TextBox，因为我想有一个从列表中选择的选项（作为建议），但是如果ItemsSource更改，我不想更改所选的文本。

I use the ComboBox for binding to string property of view model. I choose the ComboBox instead of TextBox, because i want to have an option to choose from the list (as a suggestion), but I don't want to change the selected text if the ItemsSource changes.

我试图将 IsSynchronizedWithCurrentItem 属性设置为false，但是当建议列表更改时（在所选文本的位置），文本更改为空。
似乎ComboBox记得输入的文本也在列表中，并且当该项目消失时，Text属性也被清除了。

I tried to set the IsSynchronizedWithCurrentItem property to false, but when the list of suggestions change (at the position of the selected text), the Text changes to empty. It seems that the ComboBox has remembered that the entered text was also in the list and when this item disappears, the Text property is also cleared.

所以我的问题是：这是一个错误，还是我做错了什么？
如果它是一个错误，您能建议一些解决方法吗？

So my question is: Is that a bug, or am I doing something wrong? If it is a bug, could you suggest some work around?

我创建了一个示例项目，该项目的原型如下：

I created a sample project which preproduces this:

：

<Window x:Class="TestProject1.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 IsSynchronizedWithCurrentItem="False" ItemsSource="{Binding Items}"
                  IsEditable="True" Text="{Binding SelectedText, UpdateSourceTrigger=PropertyChanged}"
                  HorizontalAlignment="Left" Margin="10,39,0,0" VerticalAlignment="Top" Width="120"/>
        <Button Click="Button_Click" Content="Update list" 
                HorizontalAlignment="Left" Margin="10,82,0,0" VerticalAlignment="Top" Width="75"/>
    </Grid>
</Window>

在后面的代码中：

public partial class MainWindow : Window, INotifyPropertyChanged
    {
        public MainWindow() {
            InitializeComponent();

            this.DataContext = this;
            Items = new List<string>() { "0", "1", "2" };
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void RaisePropertyChanged(string propertyName) {
            if (PropertyChanged != null) {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        private List<string> _items;
        public List<string> Items {// I use IEnumerable<string> with LINQ, but the effect is the same
            get { return _items; }
            set {
                if (_items != value) {
                    _items = value;
                    RaisePropertyChanged("Items");
                }
            }
        }

        private string _selectedText;
        public string SelectedText {
            get { return _selectedText; }
            set {
                if (_selectedText != value) {
                    _selectedText = value;
                    RaisePropertyChanged("SelectedText");
                }
            }
        }

        private void Button_Click(object sender, RoutedEventArgs e) {
            var changed = Items.ToList();//clone
            int index = changed.IndexOf(SelectedText);
            if (index >= 0) {
                changed[index] += "a";//just change the currently selected value
            }
            Items = changed;//update with new list
        }

    }

推荐答案

这是我解决该问题的方法：

This is my fix for that issue:

public class ComboBox : System.Windows.Controls.ComboBox
{
    private bool ignore = false;
    protected override void OnSelectionChanged(SelectionChangedEventArgs e)
    {
        if (!ignore)
        {
            base.OnSelectionChanged(e);
        }
    }

    protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
    {
        ignore = true;
        try
        {
            base.OnItemsChanged(e);
        }
        finally
        {
            ignore = false;
        }
    }
}

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