如何设置XAML Combobox的选定值？

Question

为什么以下示例中的组合框设置为空白而不是“先生”？

XAML：

<Window x:Class="TestComb82822.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <StackPanel HorizontalAlignment="Left">
        <ComboBox SelectedValue="{Binding Salutation}" Width="200">
            <ComboBoxItem>Company</ComboBoxItem>
            <ComboBoxItem>Ms.</ComboBoxItem>
            <ComboBoxItem>Mr.</ComboBoxItem>
        </ComboBox>
    </StackPanel>
</Window>

代码背后：

using System.Windows;
using System.ComponentModel;

namespace TestComb82822
{
    public partial class Window1 : Window, INotifyPropertyChanged
    {
        #region ViewModelProperty: Salutation
        private string _salutation;
        public string Salutation
        {
            get
            {
                return _salutation;
            }

            set
            {
                _salutation = value;
                OnPropertyChanged("Salutation");
            }
        }
        #endregion

        public Window1()
        {
            InitializeComponent();
            DataContext = this;
            Salutation = "Mr.";
        }

        #region INotifiedProperty Block
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        #endregion

    }
}

第二次尝试：

Bryan，SelectedItem和WindowLoaded也不起作用，这仍然使ComboBox变为空白：

XAML：

<Window x:Class="TestCombo234.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <StackPanel HorizontalAlignment="Left">
        <ComboBox SelectedItem="{Binding Salutation}" Width="200">
            <ComboBoxItem>Company</ComboBoxItem>
            <ComboBoxItem>Ms.</ComboBoxItem>
            <ComboBoxItem>Mr.</ComboBoxItem>
        </ComboBox>
    </StackPanel>
</Window>

代码背后：

using System.Windows;
using System.ComponentModel;

namespace TestCombo234
{
    public partial class Window1 : Window, INotifyPropertyChanged
    {
        #region ViewModelProperty: Salutation
        private string _salutation;
        public string Salutation
        {
            get
            {
                return _salutation;
            }

            set
            {
                _salutation = value;
                OnPropertyChanged("Salutation");
            }
        }
        #endregion

        public Window1()
        {
            InitializeComponent();
            DataContext = this;
            Loaded += new RoutedEventHandler(Window1_Loaded);
        }

        void Window1_Loaded(object sender, RoutedEventArgs e)
        {
            Salutation = "Mr.";
        }

        #region INotifiedProperty Block
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        #endregion
    }
}

Answer 1

首先，您需要设置SelectedItem而不是SelectedValue。其次，在实际设置ComboBox之前设置SelectedItem，尝试在Window加载的事件中设置SelectedItem。

Answer 2

我在这种情况下的解决方案是使用ItemIndex，即“Mr.” = 2

Answer 3

默认情况下，ComboBox确实应该选择它的第一项。但是，您正在此处创建SelectedValue的绑定，默认情况下为双向。更重要的是，在加载时，Salutation（您绑定到的）的值实际上仍为空。尝试在 Salutation = "Mr.";之前设置InitializeComponent ，一切都应该没问题。

Answer 4

您可以在后面的代码中创建List / Observable集合。

public ObservableCollection<string> Collection
        {
            get; set;
        }

例如：

<ComboBox Name="NameCombo" ItemsSource="{Binding}">

然后在Window_Loaded方法中将Observable集合设置为ComboBox的datacontext。

例如：

NameCombo.DataContext=Collection;