C# Windows Forms中checkedListBox选中项无法保存到应用设置如何解决？

问题根因 #

• 加载逻辑缺失：你仅将配置中存储的选中项集合读取到了collectionOfTags变量，没有将集合内容同步到各个CheckedListBox控件的选中状态，是加载环节出问题的核心原因。
• 初始空值未处理：首次运行时Properties.Settings.Default.DICOMTagSettings默认值为null，直接调用Add方法会触发空引用异常，导致保存失败。
• 保存逻辑有缺陷：每次保存直接往配置集合追加选中项，未清空历史记录，多次操作后会产生大量重复数据，也会干扰后续加载的匹配逻辑。

修复步骤 #

1. 确认设置项配置 #

打开项目属性的「设置」页，确认DICOMTagSettings的类型为System.Collections.Specialized.StringCollection，作用域设置为「用户」。

2. 修正代码 #

public partial class Form2 : Form
{
    readonly Form1 form1;
    StringCollection collectionOfTags = new StringCollection();

    public Form2(Form1 owner)
    {
        form1 = owner;
        InitializeComponent();
        InitializeSecondForm();
    }

    private void InitializeSecondForm()
    {
        this.Height = Properties.Settings.Default.SecondFormHeight;
        this.Width = Properties.Settings.Default.SecondFormWidth;
        this.Location = Properties.Settings.Default.SecondFormLocation;

        // 处理初始空值
        if (Properties.Settings.Default.DICOMTagSettings == null)
        {
            Properties.Settings.Default.DICOMTagSettings = new StringCollection();
        }
        collectionOfTags = Properties.Settings.Default.DICOMTagSettings;

        // 新增加载选中项的逻辑
        SetCheckedListBoxSelectedItems(checkedListBox1);
        SetCheckedListBoxSelectedItems(checkedListBox2);
        SetCheckedListBoxSelectedItems(checkedListBox3);

        this.FormClosing += SecondFormClosingEventHandler;
        this.StartPosition = FormStartPosition.Manual;
    }

    // 复用的设置选中项方法
    private void SetCheckedListBoxSelectedItems(CheckedListBox listBox)
    {
        for (int i = 0; i < listBox.Items.Count; i++)
        {
            if (collectionOfTags.Contains(listBox.Items[i].ToString()))
            {
                listBox.SetItemChecked(i, true);
            }
        }
    }

    private void SecondFormClosingEventHandler(object sender, FormClosingEventArgs e)
    {
        Properties.Settings.Default.SecondFormHeight = this.Height;
        Properties.Settings.Default.SecondFormWidth = this.Width;
        Properties.Settings.Default.SecondFormLocation = this.Location;
        Properties.Settings.Default.DICOMTagSettings = this.collectionOfTags;

        Properties.Settings.Default.Save();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        // 先清空旧的选中记录
        collectionOfTags.Clear();

        // 新增所有当前选中的项
        foreach (string s in checkedListBox1.CheckedItems)
            collectionOfTags.Add(s);
        foreach (string s in checkedListBox2.CheckedItems)
            collectionOfTags.Add(s);
        foreach (string s in checkedListBox3.CheckedItems)
            collectionOfTags.Add(s);
        
        this.Close();
    }
}

3. 验证逻辑 #

修改后运行程序，选中对应项保存后关闭窗体，再次打开窗体即可看到之前的选中状态已经被正确保留。

内容的提问来源于stack exchange，提问作者Sanktos