C＃Winforms-设置组合框选定的值 [英] C# Winforms - setting combobox selected value

问题描述

我想为组合框设置名称和值对。因此，我创建了一个名为 Item 的类，如下所示：

I want to set name and value pairs for combobox. So I created a class named Item like this:

// Content item for the combo box
private class Item
{
    private readonly string Name;
    private readonly int Value;
    private Item(string _name, int _value)
    {
        Name = _name; Value = _value;
    }
    private override string ToString()
    {
        // Generates the text shown in the combo box
        return Name;
    }
}

数据集如下：

comboBox1.DataSource = null;
comboBox1.Items.Clear();
// For example get from database continentals.
var gets = _connection.Continentals;
comboBox1.Items.Add(new Item("--- Select a continental. ---", 0));
foreach (var get in gets)
{
    comboBox1.Items.Add(new Item(get.name.Length > 40 ? get.name.Substring(0, 37) + "..." : get.name, Convert.ToInt32(get.id)));
}
// It points Africa.
comboBox1.SelectedValue = 3;

这是输出：

// 1 - Europe
// 2 - Asia
// 3 - Africa
// 4 - North America
// 5 - South America
// 6 - Australia
// 7 - Antartica

在我的示例必须选择非洲大陆，但不是。
不仅如此，例如，这段代码还从 person 表中获取数据：

In my example The Africa continental must be selected but it is not. And more than that in my edit form, for example this code gets datas from person table:

var a = _connection.persons.SingleOrDefault（x => x.id == Id）;

当我编写 comboBox2.SelectedValue = a.continental 时，必须选择非洲大陆，但不是。我没有解决问题。

When I code comboBox2.SelectedValue = a.continental, the Africa continental must be selected, but it is not. I did not solve the problem.

推荐答案

如 SelectedValue 物业文档：

As described in the SelectedValue property documentation:

属性值

包含成员值的对象 ValueMember 属性。

注释

如果未在 ValueMember ，SelectedValue返回 ToString的结果对象的方法。

Remarks
If a property is not specified in ValueMember, SelectedValue returns the results of the ToString method of the object.

要获得所需的行为，您需要公开 Name 和 Value 作为 Item 类的公共属性，并利用控件的DataSource ， ValueMember 和 DisplayMember 属性：

To get the desired behavior, you need to expose Name and Value as public properties of your Item class and utilize the DataSource, ValueMember and DisplayMember properties of the control:

// Content item for the combo box
private class Item
{
    public string Name { get; private set; }
    public int Value { get; private set; }
    private Item(string _name, int _value)
    {
        Name = _name; Value = _value;
    }
}

和示例用法：

// Build a list with items
var items = new List<Item>();
// For example get from database continentals.
var gets = _connection.Continentals;
items.Add(new Item("--- Select a continental. ---", 0));
foreach (var get in gets)
{
    items.Add(new Item(get.name.Length > 40 ? get.name.Substring(0, 37) + "..." : get.name, Convert.ToInt32(get.id)));
}
// Bind combobox list to the items
comboBox1.DisplayMember = "Name"; // will display Name property
comboBox1.ValueMember = "Value"; // will select Value property
comboBox1.DataSource = item; // assign list (will populate comboBox1.Items)

// Will select Africa
comboBox1.SelectedValue = 3;

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