组合框SelectedItem不能按预期工作

问题描述

| 我有一个组合框，它绑定到我的视图模型（

FooCollection

）上的Foo集合。我还将组合框的

SelectedItem

属性设置为类型为

Foo

的视图模型上称为

SelectedFoo

的属性。 然后，我设置FooCollection和SelectedFoo并触发适当的OnPropertyChanged事件。 我的组合框包含Foo的列表，但是组合框中显示的项目始终是列表中的第一项。但是，如果下拉组合框，则突出显示的项目是正确的项目（

SelectedFoo

）。因此，它选择正确的项目，但不显示它。

<ComboBox Grid.Row=\"5\"  ItemsSource=\"{Binding Path=FooCollection}\" 
                         SelectedItem=\"{Binding SelectedFoo,Mode=TwoWay}\" 
                         Name=\"FooSelectionControl\"/>

有谁知道如何解决这一问题？     

解决方法

嗯，对我有用。您正在使用哪种收藏？

    <ComboBox 
        SelectedItem=\"{Binding SelectedFoo,Mode=TwoWay}\"
        ItemsSource=\"{Binding FooCollection}\">
    </ComboBox>

后面的代码：

    public MainWindow()
    {
        InitializeComponent();

        DataContext = this;

        FooCollection = new BindingList<Foo>();

        var foo = new Foo(\"Alpha\");
        FooCollection.Add(foo);

        foo = new Foo(\"Beta\");
        SelectedFoo = foo;
        FooCollection.Add(foo);

        foo = new Foo(\"Gamma\");
        FooCollection.Add(foo);
    }

    public Foo SelectedFoo
    {
        get { return (Foo)GetValue(SelectedFooProperty); }
        set { SetValue(SelectedFooProperty,value); }
    }
    public static readonly DependencyProperty SelectedFooProperty =
        DependencyProperty.Register(\"SelectedFoo\",typeof(Foo),typeof(MainWindow),new UIPropertyMetadata(null));

    public BindingList<Foo> FooCollection
    {
        get { return (BindingList<Foo>)GetValue(FooCollectionProperty); }
        set { SetValue(FooCollectionProperty,value); }
    }
    public static readonly DependencyProperty FooCollectionProperty =
        DependencyProperty.Register(\"FooCollection\",typeof(BindingList<Foo>),new UIPropertyMetadata(new BindingList<Foo>()));

和Foo班，

public class Foo : INotifyPropertyChanged
{
    public Foo(string name)
    {
        _name = name;
    }

    private string _name;

    public string Name
    {
        get { return _name; }
        set
        {
            if (_name == value) return;

            _name = value;
            OnPropertyChanged(\"Name\");
        }
    }

    public override string ToString()
    {
        return Name;
    }

    #region INotifyPropertyChanged event

    ///<summary>
    ///Occurs when a property value changes.
    ///</summary>
    public event PropertyChangedEventHandler PropertyChanged;


    /// <summary>
    /// Raises the <see cref=\"PropertyChanged\"/> event for
    /// a given property.
    /// </summary>
    /// <param name=\"propertyName\">The name of the changed property.</param>
    protected void OnPropertyChanged(string propertyName)
    {
        //validate the property name in debug builds
        VerifyProperty(propertyName);

        if (PropertyChanged != null)
        {
            PropertyChanged(this,new PropertyChangedEventArgs(propertyName));
        }
    }


    /// <summary>
    /// Verifies whether the current class provides a property with a given
    /// name. This method is only invoked in debug builds,and results in
    /// a runtime exception if the <see cref=\"OnPropertyChanged\"/> method
    /// is being invoked with an invalid property name. This may happen if
    /// a property\'s name was changed but not the parameter of the property\'s
    /// invocation of <see cref=\"OnPropertyChanged\"/>.
    /// </summary>
    /// <param name=\"propertyName\">The name of the changed property.</param>
    [Conditional(\"DEBUG\")]
    private void VerifyProperty(string propertyName)
    {
        Type type = GetType();

        //look for a *public* property with the specified name
        PropertyInfo pi = type.GetProperty(propertyName);
        if (pi == null)
        {
            //there is no matching property - notify the developer
            string msg = \"OnPropertyChanged was invoked with invalid property name {0}: \";
            msg += \"{0} is not a public property of {1}.\";
            msg = String.Format(msg,propertyName,type.FullName);
            Debug.Fail(msg);
        }
    }

    #endregion
}

    ,也许尝试使用SelectedValue而不是SelectedItem。另外，请确保正确实现了Foo.Equals（）。