C# DropDownList with a Dictionary as DataSource

问题:

I want to set DataTextField and DataValueField of a Dropdownlist (languageList) using a Dictionary (list) of languageCod (en-gb) as key and language name (english) as the text to display.

Relevant Code:

string[] languageCodsList= service.LanguagesAvailable();
Dictionary<string, string> list = 
                   new Dictionary<string, string>(languageCodsList.Length);

foreach (string cod in languageCodsList)
{
    CultureInfo cul = new CultureInfo(cod);
    list.Add(cod, cul.DisplayName);
}
languageList.DataSource = list;
languageList.DataBind();

How can I set DataTextField and DataValueField?

回答1:

Like that you can set DataTextField and DataValueField of DropDownList using "Key" and "Value" texts :

    Dictionary<string, string> list = new Dictionary<string, string>();
    list.Add("item 1", "Item 1");
    list.Add("item 2", "Item 2");
    list.Add("item 3", "Item 3");
    list.Add("item 4", "Item 4");

    ddl.DataSource = list;
    ddl.DataTextField = "Value";
    ddl.DataValueField = "Key";
    ddl.DataBind();

回答2:

When a dictionary is enumerated, it will yield KeyValuePair<TKey,TValue> objects... so you just need to specify "Value" and "Key" for DataTextField and DataValueField respectively, to select the Value/Key properties.

Thanks to Joe's comment, I reread the question to get these the right way round. Normally I'd expect the "key" in the dictionary to be the text that's displayed, and the "value" to be the value fetched. Your sample code uses them the other way round though. Unless you really need them to be this way, you might want to consider writing your code as:

list.Add(cul.DisplayName, cod);

(And then changing the binding to use "Key" for DataTextField and "Value" for DataValueField, of course.)

In fact, I'd suggest that as it seems you really do want a list rather than a dictionary, you might want to reconsider using a dictionary in the first place. You could just use a List<KeyValuePair<string, string>>:

string[] languageCodsList = service.LanguagesAvailable();
var list = new List<KeyValuePair<string, string>>();

foreach (string cod in languageCodsList)
{
    CultureInfo cul = new CultureInfo(cod);
    list.Add(new KeyValuePair<string, string>(cul.DisplayName, cod));
}

Alternatively, use a list of plain CultureInfo values. LINQ makes this really easy:

var cultures = service.LanguagesAvailable()
                      .Select(language => new CultureInfo(language));
languageList.DataTextField = "DisplayName";
languageList.DataValueField = "Name";
languageList.DataSource = cultures;
languageList.DataBind();

If you're not using LINQ, you can still use a normal foreach loop:

List<CultureInfo> cultures = new List<CultureInfo>();
foreach (string cod in service.LanguagesAvailable())
{
    cultures.Add(new CultureInfo(cod));
}
languageList.DataTextField = "DisplayName";
languageList.DataValueField = "Name";
languageList.DataSource = cultures;
languageList.DataBind();

回答3:

Just use "Key" and "Value"

回答4:

If the DropDownList is declared in your aspx page and not in the codebehind, you can do it like this.

.aspx:

<asp:DropDownList ID="ddlStatus" runat="server" DataSource="<%# Statuses %>"
     DataValueField="Key" DataTextField="Value"></asp:DropDownList>

.aspx.cs:

protected void Page_Load(object sender, EventArgs e)
{
    ddlStatus.DataBind();
    // or use Page.DataBind() to bind everything
}

public Dictionary<int, string> Statuses
{
    get 
    {
        // do database/webservice lookup here to populate Dictionary
    }
};