我可以用来填充 DropDownList 的最舒服的数据类型是什么？

发布于 2024-09-15 05:39:35 字数 609 浏览 6 评论 0原文

例如，我希望用户为给定团队创建一个新的粉丝俱乐部。

显然，团队必须加载到 DropDownList 中，以便从预设的选择组中进行选择。团队列表是从数据库返回的。

截至目前，我正在做这样的事情：

//FindAll() returns IQueryable<Team>
var Teams = teamsRepo.FindAll().AsEnumarable();
myDropDownList.DataTextField = "Name";
myDropDownList.DataValueField = "ID";
myDropDownList.DataSource = Teams;
myDropDownList.DataBind();

不幸的是，当以这种方式做事时，我没有强类型属性，因此存在拼写错误 ValueField 或 TextField 的风险。

尝试获取 DropDownList 的选定值时也存在问题。使用以下代码，无论选择哪个团队，所有内容都会以 ID 1 保存。

fansite.IDTeam = myDropDownList.SelectedIndex;

关于如何改进有什么建议吗？

原文

For example, I want a user to create a new fanclub for a given Team.

Obviously the teams have to be loaded into a DropDownList so they are chosen from a pre-set choice group. The list of teams are returned from a database.

As of now I'm doing things like this:

//FindAll() returns IQueryable<Team>
var Teams = teamsRepo.FindAll().AsEnumarable();
myDropDownList.DataTextField = "Name";
myDropDownList.DataValueField = "ID";
myDropDownList.DataSource = Teams;
myDropDownList.DataBind();

Unfortunately when doing things this way I have no strongly typed attributes, so there is a risk of misspelling the ValueField or TextField.

There is also a problem when trying to get the selected value of the DropDownList. Using the following code, everything is saved with ID 1 regardless of what team was chosen.

fansite.IDTeam = myDropDownList.SelectedIndex;

Any suggestions on how to improve?

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我的痛♀有谁懂 2024-09-22 05:39:36

从您的问题来看，您似乎担心代码中数据绑定的硬编码字符串。同样的事情也曾经让我发疯。

有一种使用 lambda 方法和表达式树的好方法，它允许您摆脱硬编码字符串并以强类型方式获取属性名称：

您可以使用此类和扩展方法...

public class Nameof<T>
{
    public static string Property<TProp>(Expression<Func<T, TProp>> expression)
    {
        var body = expression.Body as MemberExpression;
        if(body == null)
            throw new ArgumentException("'expression' should be a member expression");
        return body.Member.Name;
    }
}

...并且这将允许您执行以下操作：

//instead of myDropDownList.DataTextField = "Name";
myDropDownList.DataTextField = Nameof<Team>.Property(t => t.Name);
//instead of myDropDownList.DataValueField = "ID";
myDropDownList.DataValueField = Nameof<Team>.Property(t => t.ID);

这就是我喜欢看到的；看不到硬编码的字符串文字！ :-)

From your question it seems you're concerned about the hard coded strings for the databinding in your code. The same thing used to drive me nuts too.

There is a good way of using lambda methods and expression trees that will allow you to get rid of the hard coded strings and get the property names in a strongly typed way:

You can use this class and extension method...

public class Nameof<T>
{
    public static string Property<TProp>(Expression<Func<T, TProp>> expression)
    {
        var body = expression.Body as MemberExpression;
        if(body == null)
            throw new ArgumentException("'expression' should be a member expression");
        return body.Member.Name;
    }
}

...and this will allow you to do the following:

//instead of myDropDownList.DataTextField = "Name";
myDropDownList.DataTextField = Nameof<Team>.Property(t => t.Name);
//instead of myDropDownList.DataValueField = "ID";
myDropDownList.DataValueField = Nameof<Team>.Property(t => t.ID);

That's what I like to see; not a hard coded string literal in sight! :-)

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执手闯天涯 2024-09-22 05:39:36

这正是 .NET 数据绑定的工作原理，您必须输入属性名称。

您始终可以将转换器添加到组合框项，然后调用 add (ms-doc)

至于获取所选项目的值，请尝试以下操作：

fansite.IDTeam = myDropDownList.SelectedValue;

This is exactly how .NET databinding works, you have to type in the property names.

You could always add a converter to a combobox item and then call add (ms-doc)

As far as getting the value of the selected item try this:

fansite.IDTeam = myDropDownList.SelectedValue;

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南汐寒笙箫 2024-09-22 05:39:36

（这是在ASP.Net澄清之前写的，我是从winforms的角度回答的）。

我不确定您的 Teams ID 是什么样的，但如果它们不是连续的、从零开始且没有间隙的，则使用 myDropDownList.SelectedIndex; 会给您错误的结果一条数据。

我认为您最后一行应该阅读：

fansite.IDTeam = myDropDownList.SelectedValue;

在要使用的数据类型上，我通常使用 Dictionary 作为下拉列表，并有一些辅助扩展方法来使填充更好一点。

(This was written before the ASP.Net clarification, I have answered from a winforms persepective).

I'm not sure what your Teams IDs are like, but if they are not sequential, zero based and with no gaps, using myDropDownList.SelectedIndex; will give you the wrong piece of data.

I think you last line should read:

fansite.IDTeam = myDropDownList.SelectedValue;

On the data type to use, I usually use a Dictionary<int, string> for dropdown lists, and have a few helper extension methods to make population a little nicer.

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