如何在运行时在app.config中创建新用户设置

Question

I have an Editable ComboBox. The user enters text and presses a Save button. Their text is turned into a string.

I need it at Run Time to Create a new User Setting to the app.config with the name of their string. (I think this part works now).

Then another ComboBox's Selected Item is saved to the Setting. (Object reference not set error).

This is to create a custom preset that will save each control state, checkboxes, textboxes, etc. in the program.

// Control State to be Saved to Setting
Object comboBox2Item = ComboBox2.SelectedItem;

// User Custom Text
string customText = ComboBox1.Text;

// Create New User Setting
var propertyCustom = new SettingsProperty(customText);
propertyCustom.Name = customText;
propertyCustom.PropertyType = typeof(string); 
Settings.Default.Properties.Add(propertyCustom);

// Add a Control State (string) to the Setting
Settings.Default[customText] = (string)comboBox2Item;

At this part I get an error.

Settings.Default[customText] = (string)comboBox2Item;

Exception:Thrown: "Object reference not set to an instance of an object."

I have tried setting ComboBox1.Text to an Object instead of string, with same error. The text and string is also not null.

Object customText = ComboBox1.Text;

Here's a visual of what I'm trying to do

Answer 1

Original Answer:

I haven't tried adding a new setting to the file but i have had to update it. Here is some code that I use to save and retrieve the saved changes to the file. I know it doesn't directly answer the question but should point you in the right direction as to what classes to look at and use.

I'll try to update to directly answer this question once I get some breathing time.

public static void UpdateConfig(string setting, string value, bool isUserSetting = false)
    {
        var assemblyPath = AppDomain.CurrentDomain.BaseDirectory;
        var assemblyName = "AssemblyName";

        //need to modify the configuration file, launch the server with those settings.
        var config =
            ConfigurationManager.OpenExeConfiguration(string.Format("{0}\\{1}.exe", assemblyPath, "AssemblyName"));

        //config.AppSettings.Settings["Setting"].Value = "false";
        var getSection = config.GetSection("applicationSettings");
        Console.WriteLine(getSection);

        var settingsGroup = isUserSetting
            ? config.SectionGroups["userSettings"]
            : config.SectionGroups["applicationSettings"];
        var settings =
            settingsGroup.Sections[string.Format("{0}.Properties.Settings", assemblyName)] as ClientSettingsSection;
        var settingsElement = settings.Settings.Get(setting);

        settings.Settings.Remove(settingsElement);
        settingsElement.Value.ValueXml.InnerText = value;
        settings.Settings.Add(settingsElement);

        config.Save(ConfigurationSaveMode.Modified);
        ConfigurationManager.RefreshSection("appSettings");

Edited Answer:

I did a quick google search and found an accepted answer on the MSDN forum. MSDN question . You have to call save on the properties class in order for the add to take affect. Think of a database transaction, until you call commit, it doesn't take effect.

So what appears to be missing in your code is: Properties.Settings.Default.Save(); which should be the very next line after your Settings.Default.Properties.Add(propertyCustom);