WPF：禁用组合框中的所选项目

Question

I have been going through posts for 3 hours now with no resolution. I am new to WPF and created the ComboBox below:

Unfortunately I cannot disable the highlighting of the selected item. Does anyone have a viable solution?

Code :

            <StackPanel Grid.Column="1" 
                        Margin="800,0,0,0"
                        Width="135"
                        HorizontalAlignment="Right"
                        VerticalAlignment="Center">
                <ComboBox Name="LangComboBox"
                          IsEditable="True"
                          IsReadOnly="True"
                          Text="Select Language">
                    <ComboBoxItem>English</ComboBoxItem>
                    <ComboBoxItem>Spanish</ComboBoxItem>
                    <ComboBoxItem>Both</ComboBoxItem>
                </ComboBox>
            </StackPanel>

Answer 1

I would like to clarify first of all that mine wants to be constructive answer and want to try to spread the culture of good programming. We all have always to learn about programming, me too! If you do not know a topic, it is good practice to study perhaps starting from a good book or from the official documentation of the platform.

That said let's move on to some possible approaches to your problem.

First of all, the fact that the selection in the combobox is that way is due to the basic template of the combobox that I invite you to view: https://msdn.microsoft.com/library/ms752094(v=vs.85).aspx )

What you are looking for is a different behavior of the combobox:

1. Allow display of a default value
2. Once an element is selected, the text inside it is not underlined

A first approach could be based on the ComboBox template : the combobox is constructed in such a way that, if it is editable, its template contains a textbox called PART_EditableTextBox by acting on the textbox, for example by making it disabled, you can get the result you want.

And this can be implemented in different ways:

1. Inserting a code-behind event handler that disables the textbox when the combobox is loaded
2. With an Attached behavior that allows you to add custom behaviors to the controls ( https://www.codeproject.com/Articles/28959/Introduction-to-Attached-Behaviors-in-WPF )
3. Write a custom control that maybe insert a watermark type part to your combobox

Now consider the first approach that is the fastest to implement so the code could be the following:

<ComboBox Name="LangComboBox" IsEditable="True" IsReadOnly="True" 
                          Loaded="LangComboBox_Loaded"
                          Text="Select language">
    <ComboBoxItem Content="English"/>
    <ComboBoxItem Content="Spanish"/>
    <ComboBoxItem Content="Both"/>
</ComboBox>

In the code-behind:

private void LangComboBox_Loaded(object sender, RoutedEventArgs e)
{
    ComboBox ctrl = (ComboBox)sender;
    TextBox Editable_tb = (TextBox)ctrl.Template.FindName("PART_EditableTextBox", ctrl);
    if (Editable_tb != null)
    {
        // Disable the textbox
        Editable_tb.IsEnabled = false;
    }
}

This approach, however, has drawbacks, among which the fact that if the user wants to deselect / reset the value of the combo can not do it.

So you could follow another path using the MVVM pattern.

Coming from the world of web programming you should know the MVC pattern, in WPF the most common pattern is MVVM or Model - View - ViewModel between the two patterns there are different things in common and I invite you to take a look at them: Mvvm Pattern .

You could create a class with the model that will be hosted in the combo for example:

public class Language
    {
        public int Id { get; set; }
        public string Description { get; set; }

        public Language(int id, string desc)
        {
            this.Id = id;
            this.Description = desc;
        }
    }

    public class YourDataContext : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private List<Language> _Languages;
        public List<Language> Languages
        {
            get
            {
                return _Languages;
            }
            set
            {
                _Languages = value;
                OnPropertyChanged("Languages");
            }
        }

        private Language _selectedLanguage;
        public Language SelectedLanguage
        {
            get
            {
                return _selectedLanguage;
            }
            set
            {
                _selectedLanguage = value;
                OnPropertyChanged("SelectedLanguage");

            }
        }

        public YourDataContext()
        {
            // Initialization of languages
            Languages = new List<Language>();

            Languages.Add(new Language(0, "None - Select a Language"));

            Languages.Add(new Language(1, "English"));

            Languages.Add(new Language(2, "Spanish"));

            Languages.Add(new Language(3, "Both"));

            SelectedLanguage = Languages.First();
        }

        protected virtual void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
        }
        // some other properties and commands
    }


    // Your Window class

    public MainWindow()
    {
        InitializeComponent();
        var dc = new YourDataContext();
        DataContext = dc;


    }


<ComboBox ItemsSource="{Binding Languages}"
                          DisplayMemberPath="Description"
                          SelectedItem="{Binding SelectedLanguage}"/>

Note that now the combobox is no longer editable and it is possible to reset the selection.

You can manage the selection using the model:

if(dc.SelectedLanguage.Id == 0)
    {
        //No language selected
    }

There are a lot of different ways to achieve what you want, i hope this gave you some good point to start from.

Good programming to everyone.