ComboBox.SelectedValue在窗体的构造方法中为null

问题描述

我生成了一个非常简单的代码段:

I generated a very simple code snippet:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        dt = new DataTable();
        dt.Columns.Add("ID", typeof(int));
        dt.Columns.Add("Title", typeof(string));
        dt.Rows.Add(1, "One");
        dt.Rows.Add(2, "Two");

        cmb = new ComboBox();
        cmb.DropDownStyle = ComboBoxStyle.DropDownList;
        cmb.DisplayMember = "Title";
        cmb.ValueMember = "ID";
        cmb.DataSource = dt;

        this.Controls.Add(cmb);
        cmb.SelectedValue = 2;
    }
}

当我将值设置为 cmb.SelectedValue 时， SelectedValue 为 null .

When I set the value cmb.SelectedValue, SelectedValue is null.

我知道，如果我将此代码移到 Form1_Load 处理程序中，它将按预期工作，但是我需要在Form的Constructor中使用它.

I know that if I move this code to the Form1_Load handler, it will work as expected, but I need it in Form's Constructor.

推荐答案

您可以致电 CreateControl()在窗体的构造函数中强制创建控件的句柄.

You can call CreateControl() in the Form's Constructor to force the creation of the control's handle.

阅读句柄属性:

SelectValue 属性在此之后将具有值.

The SelectValue property will have value after this point.

public Form1()
{
    InitializeComponent();

    // [...]

    this.Controls.Add(cmb);

    cmb.CreateControl();
    cmb.SelectedValue = 2;
}

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