名单 <string> 用于在UserControl中填充ComboBox的属性-C＃

Question

I have a UserControl with a ComboBox inside. I need to populate ComboBox items using a List property but I get the error below in designer:

constructor on type 'system.string' not found

and Here is my code:

public List<string> comboItems
{
    get
    {
        List<string> n = new List<string>();
        foreach (var i in comboBox1.Items)
            n.Add(i.ToString());
        return n;
    }
    set
    {
        if (comboItems == null)
            comboItems = new List<string>();
        foreach (var i in value)
            comboBox1.Items.Add(i);
    }
}

Answer 1

In general it's not a good idea to expose items of the ComboBox as a string[] or as a List<string> because users may set ComboItems[0] = "something" but it will not change the first element of the combo box items.

But if you are looking for a solution to get rid of the error message which you receive in designer, instead of a List<string> use a string[] and change your code to:

public string[] ComboItems {
    get {
        return comboBox1.Items.Cast<object>()
                .Select(x => x.ToString()).ToArray();
    }
    set {
        comboBox1.Items.Clear();
        comboBox1.Items.AddRange(value);
    }
}

Note

This is the correct way of exposing Items property of a ComboBox in a UserControl :

[Editor("System.Windows.Forms.Design.ListControlStringCollectionEditor, " +
    "System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a",
    typeof(UITypeEditor))]
[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
public ComboBox.ObjectCollection ComboItems {
    get { return comboBox1.Items; }
}

Answer 2

You can use ObjectCollection for your property and asign it directly to your combobox. This way you are allowed to use the design editor.

[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
public ObjectCollection ComboItems
{
    get
    {
        return comboBox1.Items;
    }
    set
    {
        comboBox1.Items.Clear();
        foreach (var i in value)
            comboBox1.Items.Add(i);
    }
}